Downdraught prevention chimney cowls

ttm · 12-11-2009 8:35pm

NutleyAFC wrote: »

First time posting - anywhere, so please excuse me if I'm duplicating a previous question.

We built an extension with a new chimney. The builder started constructing a standard flue and heart opening. We needed a larger fireplace so I assume he just widened/heightened the opening without doing anything to the flue.

I now know there is some flue/opening ratio.

The room fills with smoke.

When I go to buy a cowl and explain my problem I'm advised to buy an electric cowl. Then when I went to buy an electric cowl I was recommended to start with a standard cowl.

So far I haven't had any luck getting a chimney expert to come out and diagnose the problem.

Any advice? Is there someone/a company that will fix this problem?

Thanks.

So why do you think a cowl will help if the fireplace has an incorrect flue/opening ratio?

This is the FAQ from a cowl company and they say to sort that out before fitting a cowl.

sooty_soupy · 12-11-2009 9:02pm

Hi guys. Just to confirm what everyone has been saying here. A cowl is not often a solution for many problems in my experience. They are a "hit and miss" thing really and are so inconsistent, I have known times when they work beautifully for one client, then the neighbour across the street gets one and it is a disaster.

Ratio problems are all to often a problem when builders make these wonderful fireplace opening with a view to installing a lovely dog grate to burn big logs like the old stately home fireplaces of yesteryear. The issue is that the very chimney dimensions of yesteryear would have been of such proportions, that children could climb up them. The huge smoke chambers and expansive openings in these chimneys meant that big fireplaces were not a problem, and the estate owners would have had the servants bring in the wood for such fireplaces that would have burned for most of the day and resembled half trees.

The standard chimney North and South of the border would have a lining system commonly of 200mm diameter, or 8". (these are often called 9" liners) The restriction in the diameter of such liners, reduces air flow through the flue, and when the opening of the fireplace is larger, this in turn leads to a smoke spillage into the room. A cure for the mild problem is to raise the grate higher in the opening, effectively reducing the square inch opening of the firebed to top of fireplace dimension. The other common way to resolve the issue was to form some sort of smoke canopy, again in an effort to reduce the cross section of the opening....there is a reason why standard fireplaces are 16-18" wide and about 21.5" high. An electric fan is the most effective solution, however they spin on a bearing, as do the rotating cowls, and can be a pain in the neck when soot and smoke along with the cold weather cause condensate to build up on the product and seize it from spinning....get the ladders on standby, because the cowl that should spin but doesn't is a restriction or blockage in the flue and you only thought you had a smoke problem before. If this happens to you on Christmas day when the family are around, you may crawl out of the smoke filled room and take your turkey with you.

A simple solution, which is more efficient too is to fit a stove if the opening is large enough. You will reduce heat loss through the open chimney and also if you have a cowl or fan fitted, it encourages more heat from the fire to be drawn away up the chimney, leaving you with a fireplace that might look nice, and doesn't smoke any more, but the heat return you are getting from the fuel is diabolical, where as a stove is between 75 -80% efficient.

sooty_soupy · 12-11-2009 9:11pm

Miltown can you confirm if the VE pipe (the black pipe usually) is fitted into the existing clay lined chimney. I have a few reservations about the flue travelling horizontally at all, and especially 12" which is more than allowed by your current building regs in the south. The other thing that I would like to know is if the VE pipe is sealed into the existing chimney, or merely rammed up in, with a bend at the bottom to turn into the horizontal. If it isn't sealed, then the natural draft in teh chimney flue is not being concentrated on the firebox of the stove which will effect the performance of the stove. I would also expect a boiler stove to give more problems than a dry stove if the flue has not been correctly steel lined with condensates in the chimney, which are like tars deposits. Boiler stoves are always a problem because the cooling effect on the gasses before they get into the flue are effecting the temperature, and therefore the speed at which they rise through the flue. I would be more inclined to speak to a solid fuel technician or chimney technician as opposed to a plumber, certified or not, about the science of how chimneys work. My green grocer doesn't fix my fridge freezer....if you know what I mean. If you can get me these answers and PM me, I'll try to help you out.

David

SineadCHAN · 24-11-2009 4:00pm

Hi all, this is my first time posting... I moved into a council house last year. It is a two bedroom house and the hotpress is inbetween both bedrooms. The houses have solar panels so the boiler is massive.

Recently with the bad weather, there is noises (sounds like a lawnmower or chainsaw) coming out of the hotpress and as the walls are paper thin we can hear it in both bedrooms.... and it only happens when it is windy outside.

I thought myself that maybe there was a hole in the hotpress and the wind was coming in through there and making a noise and my uncle told me that I needed a cowl for the chimney as the noise was the wind coming down the chimney?

Can anyone help me with this because some nights the sound is unbearable. Anyone ever hear of this before and any suggestions on what I can do???

ttm · 24-11-2009 5:42pm

SineadCHAN wrote: »

Hi all, this is my first time posting... I moved into a council house last year. It is a two bedroom house and the hotpress is inbetween both bedrooms. The houses have solar panels so the boiler is massive.

Recently with the bad weather, there is noises (sounds like a lawnmower or chainsaw) coming out of the hotpress and as the walls are paper thin we can hear it in both bedrooms.... and it only happens when it is windy outside.

I thought myself that maybe there was a hole in the hotpress and the wind was coming in through there and making a noise and my uncle told me that I needed a cowl for the chimney as the noise was the wind coming down the chimney?

Can anyone help me with this because some nights the sound is unbearable. Anyone ever hear of this before and any suggestions on what I can do???

Do you use the chimney for a fire?

Any chance the sound is like a 20ft long metal pipe vibrating inside a 20ft long concrete tube? If so it might be the liner is just hanging there and could do with some vermiculite to help insulate it, support it and stop it from vibrating. If you don't have a liner then its not that

SineadCHAN · 25-11-2009 3:45pm

Hi, yes I do use the chimney for the fire..

no it doesn't sound like that, it's like when theres a gush of wind and the noise comes, we can only hear it upstairs.. and the noise is coming from the hotpress. It doesn't affect the fire or theres no noise in the sitting room either??

Tomnail · 27-11-2009 10:06pm

sooty_soupy wrote: »

Hi Omron, welcome to the forum. The condition you have is almost definitely siphonage. The condition arises where one flue chamber is cooler, therefore at an unequal pressure to that of the one being used. On calm days especially you will run into a problem where the colder flue can actually suck the smoke into the room, so your suspicions were almost correct. I would be hesitant to spend money on anti down draught cowls etc, as I don't believe this is actually the case. You have tried what I would have suggested in that if a plastic bag temporarily is used to block the offending flue and there was no problem, the simple cure is remove the bag and replace the LIVE chimney pot with a taller pot, which staggers the termination points, thus curing the problem and not affecting the performance of either.

Hope this helps.

best regards

David

Folks, just came on this board. I've been through the mill with my chimneys since completing contstruction three years ago. I recognize lots of the issues being raised above. Sooty soupy, your contributions are excellent if I may say so. Perhaps you can give me some guidance. I have a question or two but will tell you our saga first...

We get down draught in two chimneys when there's easterly wind. First, I bought expensive vaned stainless steel cowls from the UK. Didn't work. I went back to supplier and asked whether their rotating cowls might work better. In fairness supplier said, (like Sooty warns on this forum) that cowls are a hit and miss solution. We have a roof hip to the west of the offending chimney pots and even though the clearance from the tops of the pots is technically sufficient, supplier said it may come down to needing to raise the chimneys. We did both. Thinking, belt and braces, we replaced the chimney pots with 1.9m tallboy chimney pots and put the rotating cowls on top of those. (big house, big job requiring cherry pickers etc.). I thought at least now I'm finished building the bloody house. But the saga continues. With the winds two weeks ago we got two rooms full of smoke again.

Sooty, you suggestion to other posters about the dimensions of the flu vs the open fireplace c.f. the enormous flus in old houses would be my next line of investigation, except that one of the chimneys supplies a stove and the other a fireplace. Both are equally affected.

Also don't think air starvation in the house is the issue, as you say it may be in some new houses. There's a ample flow of air inside the building.

So now I'm looking back at one of your earlier comments - that a fan can save a lot of trouble! Haven't heard of them before so two basic questions:
typically, how regularly do fans need maintenance? (critical issue with my house as safe access is only via mechanical boom and I don't want to be hiring those more often than once every few years)
and
how are they powered? (cable right down the flu, cable through wall of the flu part way down, battery?)

Cheers

Tom

mad DIY · 07-12-2009 3:32pm

ttm wrote: »

Do you use the chimney for a fire?

Any chance the sound is like a 20ft long metal pipe vibrating inside a 20ft long concrete tube? If so it might be the liner is just hanging there and could do with some vermiculite to help insulate it, support it and stop it from vibrating. If you don't have a liner then its not that

So, if I have just had a metal liner installed into a concrete flue, and its now howling in the wind into the fireplace like a helicopter is stuck up it having a fight with an express train, dispite having a Chinese hat cowl on it, does this mean the flue is installed incorrectly, or do these things need time to settle down after being installed ? Would appreciate any advice.

Bruffkid · 23-02-2010 2:04pm

ttm wrote: »

While trying not to say whether your stove is set up correctly or not I'd check if the short horizontal section at the back of the stove is clear (also check and sweep the flu attached to the stove) and check that the pipe that goes up the chimney is sealed in chimney with no major air gaps.

Hi I also have a Stove and experienced the same i have back to back fire place son on Saturday i put a anti-downdraught spinner cowl on the chimney and cleaned he Stove it helped a lot but still smokes a little when the door is opened. my question is should i have put another cowl on the second chimney or add another section to the Stove Outlet. Cheers Bruffkid

ttm · 26-02-2010 1:12am

Bruffkid wrote: »

Hi I also have a Stove and experienced the same i have back to back fire place son on Saturday i put a anti-downdraught spinner cowl on the chimney and cleaned he Stove it helped a lot but still smokes a little when the door is opened. my question is should i have put another cowl on the second chimney or add another section to the Stove Outlet. Cheers Bruffkid

Have to check this, so excuse if this is a dumb question but does this little bit of smoke occur just as you open the door and then stop after a couple of seconds or is their always a problem when the doors open?

Reason I ask is if the stove is closed off and you open the stove fire door quickly you are sucking smoke into the room faster than its going up the chinmey so untill it starts drawing back up the chimney again there will be a small bit of smoke. In most cases the answer is to open up the top damper (if there is one) and the air vent before opening the door and then to open it slowly.

Apart from that you need to explain a bit more how your chimneys are set up? Provided there is only one stove connected to one chimney and the other chimney is separate you shouldn't have to do anything to the second chimney (unless is pulling smoke back down). Extra height on a chimney is nearly always good but I'm not sure why you would need it?The one thing you don't need unless you use the second chimney is another cowl.

bobafet · 06-09-2010 2:45pm

I hope someone can advise me. I know this is probably on here somewhere but said i would ask again.

I recently bought a house (3 bed semi-detached) built in 1950s. Over the past few months I have noticed loud wind coming from the fireplace and the odd bit of sut coming into the sitting room.

There were 4 fires in the house, two are blocked, one is gas and the other is an open fire.

I have been looking at cowls and was thinking of three rain and bird cowl, one would be for the gas stack and the other two for the closed up fire places. I was looking at the spinning cowl, static cowl and the chimney closer for the open fire but not sure if any of these will work to suit the problem.

Any help would be much appreciated.

flyguy · 12-12-2010 8:12pm

Wonder if the cowl experts can answer my question.
We have a gazco hole in the wall gas fire (glass fronted/sealed unit).
Only in very windy conditions there seems to be a downdraft causing cold air coming in around the unit (seals are fine). There is no problem with the fire/flames even in the windy conditions. Was thinking of fitting the MAD anti-downdraught cowl http://www.kbf.ie/accessories/chimney-cowls/chimney-cowls
I'm just wondering if these units increase the updraught through the chimney 'cause the chimney works fine and I don't want to increase the updraught so much that all the heat will be draughted out...
Thanks!

paddy147 · 12-12-2010 8:15pm

I had this stainless steel anti bird and anti down draught cowl fitted when I had my multi fuel stove and liner fitted.

Works a treat too.:)

pauljw11 · 16-10-2011 7:46pm

Hi--I am having problems with a smoking chimnney for a solid fuel stove in our kitchen. I have been reading various posts here and other places. I am inclined to go for a "H-Cowl" but I am concerned that the problem is due to "pressure difference" problems rather than a down draft as such. The problemonly occurs when the wind is from a certain direction, also, if I open the door to the kitchen the stove will stop smoking unless the wind is very strong. Usually once the fire gets going the smoking will stop. Any advice anyone?

PeteHeat · 16-10-2011 9:27pm

Hi,

Appears you may need to install a proper vent in the room as the stove works with the room door open.

If you have a small top opening window in the room try using the stove with the window open.

May also be a problem caused by a flue adaptor as the old type 8" flue takes too long to heat up to provide sufficient draught "once the fire gets going the smoking will stop"

If the problem is worse due to certain wind direction the top of the chimney may be too low.

A "H cowl" is possibly one of the better solutions available however it will not compensate for poor ventilation or the possible build up of condensate in an unlined flue.

.

pauljw11 · 17-10-2011 9:53am

Thanks for that. The house is only ten years andthe chimney is lined, it is however too low, and the advice we have had is that it would be a major major job to raise it above the level of the ridge of the roof. There are no windows on the side of the room that the stove is, and opening the windows on the of the other side does not help. I am inclined to givethe H -cowl a go, and if it does not work reconsider. Paul

PeteHeat · 17-10-2011 11:13am

pauljw11 wrote: »

Thanks for that. The house is only ten years andthe chimney is lined, it is however too low, and the advice we have had is that it would be a major major job to raise it above the level of the ridge of the roof. There are no windows on the side of the room that the stove is, and opening the windows on the of the other side does not help. I am inclined to givethe H -cowl a go, and if it does not work reconsider. Paul

Hi,

The H cowl tends to look a bit ugly, so one solution we tried for a customer that worked was we got a 2m length of stainless steel flue fabricated with a collar at 1.2m to fit over the existing chimney pot and fitted it into the existing flue.

The end result was a flue extension of 800mm which was above the level of downward pressure that was hardly noticable but more important it worked.

.

.

pauljw11 · 17-10-2011 11:53am

Thanks oncemore--unfortunately we are in County Galway, and you appear to be in the East, but thanks for all your advice. If there is general downward pressure (as opposed to a downdraft) should a H-cowl do the trick? Where it is is not especially visible.

PeteHeat · 17-10-2011 12:43pm

Hi,

I was not looking for an order from you

any stove installer or flue supplier should be able to the same job.

The problem with fitting any cowl within the down draught area is it can not perform 100% the down draught area on a roof is hard to describe so I attached two images that are supposed to be on our web site.

On chimney details if the flue terminates within the guide area the wind can flow down the open flue causing resistance whereas if the flue is over the wind turbulance area it has a good draw.

On stack effect describes how ventilation and air movement in the building are important.

I hope this helps,

.

golfbgud · 17-10-2011 1:41pm

PeteHeat wrote: »

Hi,

Appears you may need to install a proper vent in the room as the stove works with the room door open.

If you have a small top opening window in the room try using the stove with the window open.

May also be a problem caused by a flue adaptor as the old type 8" flue takes too long to heat up to provide sufficient draught "once the fire gets going the smoking will stop"

If the problem is worse due to certain wind direction the top of the chimney may be too low.

A "H cowl" is possibly one of the better solutions available however it will not compensate for poor ventilation or the possible build up of condensate in an unlined flue.

.

I too am suffering from downdraught issues. Semi detached 4 bedroom house with two rooms with open fires - separate flues side by side in same chimney. Smoke was more noticeable after we upgraded the outer windows and doors and blocked up an adjoining door between the 2 rooms which have the fireplaces. The Missus is keen for a stove but I need to understand what the issue is first and before introducing yet another unknown!

My guess is that the chimney protrusion over the ridge tiles is not high enough? How is this calculated? When I look at the next houses up the road the chimneys are taller?

If I take a few pics can someone advise me?

Thanks - Gerry.

PeteHeat · 17-10-2011 2:39pm

Hi Gerry,

Looks like you answered your own question, upgraded windows most likely removed draughts (aka advantitious air supply) closed up a door preventing a through flow of air, chimney possibly too low, should be at the very least 600mm over the ridge preferably 1 metre.

.

golfbgud · 17-10-2011 2:53pm

PeteHeat wrote: »

Hi Gerry,

Looks like you answered your own question, upgraded windows most likely removed draughts (aka advantitious air supply) closed up a door preventing a through flow of air, chimney possibly too low, should be at the very least 600mm over the ridge preferably 1 metre.

.

Thanks Peter.
Is this a job for a builder, chimney specialist, nixer or Other?
I will take pictures to expand on my theory...

golfbgud · 17-10-2011 8:07pm

golfbgud wrote: »

Thanks Peter.
Is this a job for a builder, chimney specialist, nixer or Other?
I will take pictures to expand on my theory...

(1) Picture 665 shows my chimney and my attached neighbour - rear view.

(2) Picture 666 my house.

(3) Picture 668 is the next house up the street which appears to have taller chimneys. These houses were built after mine.

(4) Picture 670 - my house from front.

(5) Picture 671 - next house up street - front view.

PeteHeat · 17-10-2011 9:23pm

Hi,

They were a bit mean with your chimney and the adjoining house an extra block wouldn't have broken the bank when being built, that said I don't see any reason why they shouldn't work as there is no sign of big trees (shadows) and I expect if levelled the top of the flue is 600mm from the ridge or very close to it.

I can only see one vent in the back wall of the house possibly for the kitchen which may help explain where the air supply has gone when you closed up the door and fitted new windows.

I suggest that you open one of the top windows as that will do the same job as a vent (on a temporary basis) best to find a solution before doing any work.

If installing a stove I suggest a permanent vent is fitted in the room, there is a good vent that does not cause draughts when providing the air for the fire / stove.

.

golfbgud · 17-10-2011 10:44pm

PeteHeat wrote: »

Hi,

They were a bit mean with your chimney and the adjoining house an extra block wouldn't have broken the bank when being built, that said I don't see any reason why they shouldn't work as there is no sign of big trees (shadows) and I expect if levelled the top of the flue is 600mm from the ridge or very close to it.

I can only see one vent in the back wall of the house possibly for the kitchen which may help explain where the air supply has gone when you closed up the door and fitted new windows.

I suggest that you open one of the top windows as that will do the same job as a vent (on a temporary basis) best to find a solution before doing any work.

.

I should have stated that I installed a wall vent in both rooms where there were fireplaces.......the vent you see is in the livingroom and this room has a fireplace with a backboiler. Its seldom used now as I have added an oil burner. When its lit, I believe the smoke is coming down the opposite chimney and blackening the room!

The last guy I had in to look at a stove option was less informed than I was and I'm not in that business!

Here's a picture of the rear of the garden where there are some trees - not sure if this has an effect?
If installing a stove I suggest a permanent vent is fitted in the room, there is a good vent that does not cause draughts when providing the air for the fire / stove.

Bruffkid · 17-10-2011 11:22pm

Hi pauljw11
i also had that problem i have two fireplaces and open fire and a stove back to back so i first put a spinning cowl that did not work so i got in contact with a expert who advised me that a h cowl was the one for me so he took down the spinner and replaced it with a h cowl also i goth them both cleaned and i have not looked back.. hope this helps

PeteHeat · 18-10-2011 1:28am

golfbgud wrote: »

I should have stated that I installed a wall vent in both rooms where there were fireplaces.......the vent you see is in the livingroom and this room has a fireplace with a backboiler. Its seldom used now as I have added an oil burner. When its lit, I believe the smoke is coming down the opposite chimney and blackening the room!

The last guy I had in to look at a stove option was less informed than I was and I'm not in that business!

Here's a picture of the rear of the garden where there are some trees - not sure if this has an effect?
If installing a stove I suggest a permanent vent is fitted in the room, there is a good vent that does not cause draughts when providing the air for the fire / stove.

That is a different problem, smoke from one flue to another can have a number of different causes.

It could be a simple uneven pressure problem which can be caused by using a kitchen extractor fan / hood, or the smoke could be crossing from one flue to another I have seen this before in houses of a similar age to yours.

The trees look far enough away from the house not to be causing a problem but can only be ruled out by a proper site visit.

You need someone who knows what they are doing to carry out a spillage test, I am not ruling out a cowl as the fix but going on what you have told me further investigation is needed for safety reasons.

Do not install a stove until this problem is resolved as stoves do not fix chimney problems.

.

mollp · 20-10-2011 11:07pm

Hi everyone,
Have been reading thru this thread with interest as was about to go out and buy a spinner cowl tomorrow but now am not sure if it would help our problem and would be grateful for any advice.
Last year we replaced our open fire with a stove as we could not keep the fire fed with solid fuel. Because of the exposed rural location of our house the draught up our chimney is extremely strong. We would have to replace our fire brick and sides yearly. We thought that replacing with a stove would help and to an extent it has but we still found that the level of heat was not huge from the stove. We feel that this is due to the strong draught pulling the heat up the stove flue. Even with the front and top dampers closed or almost closed there is still a pull up the chimney.
Any suggestions? An engineer colleague of my hubbys advised a spinner cowl but having read replies am wondering if a H cowl would be better? Any advice welcomed. Many thanks.
Mary

luap_42 · 07-12-2011 5:09pm

mollp wrote: »

Hi everyone,
Have been reading thru this thread with interest as was about to go out and buy a spinner cowl tomorrow but now am not sure if it would help our problem and would be grateful for any advice.
Last year we replaced our open fire with a stove as we could not keep the fire fed with solid fuel. Because of the exposed rural location of our house the draught up our chimney is extremely strong. We would have to replace our fire brick and sides yearly. We thought that replacing with a stove would help and to an extent it has but we still found that the level of heat was not huge from the stove. We feel that this is due to the strong draught pulling the heat up the stove flue. Even with the front and top dampers closed or almost closed there is still a pull up the chimney.
Any suggestions? An engineer colleague of my hubbys advised a spinner cowl but having read replies am wondering if a H cowl would be better? Any advice welcomed. Many thanks.
Mary

I too have this exact problem. I live three miles from the west coast and endure regular heavy winds. The suction up the flue is amazing. If I access the flue on a windy day it is like putting your hand inside a vaccuum cleaner pipe. When lit the fire roars literally, and I cannot damp it down below a roaring fire in such condiftions. If I open it up in a gale even for a minute, it feels, sounds and looks like I have an Apollo rocket in my living room. Smokeless firelogs are gone in 40 minutes, when they should last 2 hours or more. I'm thinking a H cowl with bird protection mesh is the ideal solution. Any opinions out there?

PeteHeat · 08-12-2011 12:38am

Hi,

Two possible solutions :

A draught stabilisor doesn't look too good and draws air from the room instead of heat from the stove but is designed to prevent the up draught from pulling heat from the appliance.

The second would be to install a damper in the flue which can be closed to reduce the up draught, it must be the correct size to prevent closing the flue completely, but it will restore a level of control over the flue draught.

.

luap_42 · 09-12-2011 5:18pm

Thanks Pete, I forgot to mention one important thing. I have this huge updraught problem with an insert stove as opposed to an open fire. Therefore I cannot put a damper in the chimney as I have no access to it once the stove is in place. I think the damper in the stove is not fully closing as I cannot stop the fire roaring under windy conditions. However, maybe with enough wind and my obviously well operating flue updraught they combine to overcome the stoves primary air damper. It is a Stovax Riva 55, and I was certainly not expecting this problem.

Spindance7 · 26-01-2012 2:46pm

If you want to solve a down draught problem invest in a Windkat. For the past 12 months we've spent alot of money trying many different anti down draught cowls (H-Cowls, Spinning cowls etc) and none of them solved our problem. Through pure persistence we decided not to give up and bought a Windkat thanks to great assistence from Karoly at Windkat.co.uk . Problem solved 100% , we are still amazed at how effective the Windkat is over all other options. Our only regret is that we didn't discover the Windkat 12 months ago.

pauljw11 · 26-01-2012 5:21pm

Thanks---a couple of months back we mentioned the problem to a local builder who was replacing a couple of ridge tiles after a storm, and he replaced the cowl that was there with one he happened to have--it hasn't cured the problem, but things are certainly a lot better then they were, but we may well try the Windkat at a later date.

Spindance7 · 26-01-2012 5:27pm

If you do decide to try the Windkat they will offer you your money back within a certail period of time if you are not entirely satisfied , now thats confidence for you. Best of luck.

danhan · 18-10-2012 10:03pm

Hi
My problem is slightly different, i had my stove installed, it all worked fine, but neighbour came around complaining about smoke going into his front room, he has open gas fire.
He had his chimney inspected and all was fine, so i had my chimney lined, thinking there was probally some kind of damage somewhere!!
Next day he came round again, still the same problem...WTF
Looking at our chimney pots, they are very close together, almost touching infact, he a kind of chinese hat cap cowl
Thanks for reading, please help its doing my brain in!!

sbkenn · 20-10-2012 12:00pm

I can get H type made in stainless for a lot less than €200
I am about to get (a 4")one made for my houseboat, which has horrendous downdraft problems caused by turbulence over the harbour wall. I will use reclaimed steel as 1) I am broke, and 2) no-one will get close enough to notice the difference.
H type are almost always used on boats.

padraic mchale wrote: »

Hi Rooferpete

i have a down draught problem and i had a guy look at it. He also recommended the H Cowl but they seem to be very expensive €290 euro each plus 100 euro installation cost. This is for a terracota cowl. Do you know of anywhere cheaper?

thanks,
Padraic

luap_42 · 22-10-2012 1:29am

luap_42 wrote: »

Thanks Pete, I forgot to mention one important thing. I have this huge updraught problem with an insert stove as opposed to an open fire. Therefore I cannot put a damper in the chimney as I have no access to it once the stove is in place. I think the damper in the stove is not fully closing as I cannot stop the fire roaring under windy conditions. However, maybe with enough wind and my obviously well operating flue updraught they combine to overcome the stoves primary air damper. It is a Stovax Riva 55, and I was certainly not expecting this problem.

Just a follow up post. The damper in my Stovax Riva 55 was working perfectly. Had it checked under warranty. Had to look elsewhere for the problem and solution. I have mostly solved the excessive updraught problem, by changing the cowl to an aerocowl. This has three sloping rings arranged around three vertical rods in layers with a solid disc between the top two of the layers. It is made of heavy aluminium. The whole assembly has a clamping ring larger than my terracotta chimney pot which it screws onto with three screw on bolts. The wind blows over the disc and half of that gust is diverted upwards away from the top of the flue The disc also acts as the rain hat for the cowl/flue. Cost about €100. It is much better than before, but still draws too much during very heavy wind. I may remove and disassemble it, and try moving the disc to between the bottom two rings layers instead of where it is in the top two rings layers. Other than really heavy winds it has solved the problem of excessive updraught.

flyguy · 22-10-2012 9:53am

danhan wrote: »

Hi
My problem is slightly different, i had my stove installed, it all worked fine, but neighbour came around complaining about smoke going into his front room, he has open gas fire.
He had his chimney inspected and all was fine, so i had my chimney lined, thinking there was probally some kind of damage somewhere!!
Next day he came round again, still the same problem...WTF
Looking at our chimney pots, they are very close together, almost touching infact, he a kind of chinese hat cap cowl
Thanks for reading, please help its doing my brain in!!

Not an expert in this field at all, but seems that your neighbour might have a downdraft; the smoke from your chimney blows down his...
Can think of 2 ways to fix this; your neighbour needs to fit a different cowl or you might be able to raise/extend you chimney so smokes exits higher/further away.
Like I said I'm no expert so maybe let a professional look at it, but since you haven't gotten a reply here I thought I would...

sooty_soupy · 25-10-2012 9:28am

Sounds like a simple syphonage problem. This occurs when you have chimney pot terminating at the same level in close proximity to each other. It is more of a problem if one chimney is used more than the other. Warm flue gases travel up your chimney without too much problem and exit the chimney as they should. If you have a cowl or cap on you chimney this slows down the chance of the smoke dispersing, so it can be a hinderance to have such a device unless you absolutely need it. Now this is where the science happens. Warm gasses rise, and cold air sinks. If your neighbours chimney is not being used that often the chimney will be cold…which is why people complain of a cold draught coming from a seldom used fireplace, and why a dormant fireplace takes a while to get going when you try to light it. This sinking cold air can drag smoke down his flue, and critically with your neighbours cowl, the smoke is being trapped above his pot.
Flyguy is barking up the right tree. If you put on a taller chimney pot, it should solve the problem. I would have had your neighbour put a plastic bag over his chimney pot for a week to see if this was the problem BEFORE I flue lined the chimney, and to be honest, I would question the knowledge of the person who carried out the lining, before exploring all other avenues.
I would also make sure there is enough ventilation in the room for the stove. Anything over 5kw needs additional vents in the wall. By doing so you give the chimney the air it needs to get rid of the gasses quickly up the flue, but also this ventilation brings the oxygen back into the room that the stove is burning off…if you have any concerns about Carbon Monoxide, this is something very often overlooked by the Mickey Mouse stove companies, but has cost lives.

sooty_soupy · 25-10-2012 9:44am

There is a train of thought in the community that a stove will solve numerous problems with chimneys and this can be the case. What is often the main issue with this concept is peoples budgets tend to find them buying a less expensive stove. This is where things can get out of hand very quickly. If you have purchased a stove that has no adjustment on the door handle or hinge you are in trouble straight away. Rope seals on the door are designed to make a airtight seal, but will compress in a short time after use. If you can not compensate for this compression, your door becomes to your stove, like the sheet of newspaper is to the open fire, and away goes your log supply, and heat with it. The other issue is the cheap crap flooding the country in hardware shops and plumbing counters claiming to be cast iron….for less than £500 I don't bloody think so. Iron Ore taken from the ground, smelted and poured into moles makes cast iron….think Victorian fireplaces, still here today. What the grates and stoves of today are made of is PIG IRON, resmelted scrap metal sent to China. Cheaper raw material, poured into moles, and the impurities mean it is making the journey back to China in a few years after you scrap it for what it is. These plates are all too often held together using a fire cement compound. If you have ever used fire clay or cement you will know it is an ongoing fight as it dries and turns to dust. On this basis the stove can get whatever oxygen and air it needs irrelevant of what you do with the air controls the manufacturer gives you. This is why a lot of the industry specialists will state that a heavy steel stove is more controllable. It is fair to say that cast units will hold heat longer after they go out, but if the airtight steel stoves stay in for longer, as they are more airtight, then holding heat when they go out is not an issue, because you just don't let it go out if you don't want to. Our Clearview stove stayed in last night from 10pm until we got up at 8am on one good sized Ash log. Does exactly what it says on the tin.

Brainy Smurf · 21-04-2013 10:18am

Hi guys,

I have 2 major problems with downdrafts in 2 rooms.

Room 1
I have a fireplace in a room that I don't use that much at the moment.
When it is windy, there is desperate whistling coming from the room when the door is closed. I assume that this is caused by downdraft.

Would a cowl fix this problem? can anyone recommend someone to install this in the Kilkenny area?

Room 2
In the other room which we always use we have the same problem with whistling but when we have the fire lighting in this room, (and the doors are closed) you can feel the air being sucked in through any gaps around the doors. I assume the fire when lighting in sucking in oxygen from everywhere to burn the fuel but you can really feel the air being sucked into the room. By the way, the room never gets that warm either.
Anything I can do to stop this?

(We do not have a problem with smoke coming into the room hen it is windy.)

Insert Stove
Finally, does anyone have any recommendations for an insert stove (about 6 or 7 KW output). I am not a fan of the look of the free standing stoves even though they would give out a lot more heat.

Any advice welcome.

sbkenn · 21-04-2013 12:51pm

A lot of air needs to go up the chimney. The only way to cure the whispering is to provide a controlled air source, possibly by providing a duct opening close to the fire.

luap_42 · 22-04-2013 4:42pm

Brainy Smurf wrote: »

Room 1
I have a fireplace in a room that I don't use that much at the moment.
When it is windy, there is desperate whistling coming from the room when the door is closed. I assume that this is caused by downdraft.

If you are not using this fireplace, then either get a chimney balloon or make one yourself. Basically something that will fill the flue and stop wind coming down into the room. Just make sure you have a wall or window vent in that room. If you are occassionally using the fireplace, then a chimney damper will do the job as it can be shut, or opened to whatever amount is required for your fire when lit. You can buy a cowl that will close off the pot completely, or one to divert some of the breeze away from blowing down the flue, but they are not cheap and require someone to go up on your roof to install.

Brainy Smurf wrote: »

Room 2
In the other room which we always use we have the same problem with whistling but when we have the fire lighting in this room, (and the doors are closed) you can feel the air being sucked in through any gaps around the doors. I assume the fire when lighting in sucking in oxygen from everywhere to burn the fuel but you can really feel the air being sucked into the room. By the way, the room never gets that warm either.
Anything I can do to stop this?

(We do not have a problem with smoke coming into the room hen it is windy.)

A chimney damper will slow down the updraught, and reduce breeze being dragged under the doors. These are usually sold including installation and are only suitable for open fireplaces. You can insulate the bottom of the doors with a door draught flap which will reduce the gap and slow down the cold air coming in. Again make sure you have a wall vent or window vents to ensure you have some ventilation in the room.

Brainy Smurf wrote: »

Insert Stove
Finally, does anyone have any recommendations for an insert stove (about 6 or 7 KW output). I am not a fan of the look of the free standing stoves even though they would give out a lot more heat.

I have a Stovax Riva 55 which is excellent. The maximum heat output is 8KW. If you put an insert stove into the room with the updraught and whistling you will gain more control over the air used/fuel burned, and may also solve the draught/whistling problems, but you will still need to draughtproof the gaps beneath the doors of the room. To get a good quality insert stove you should contact a stove supplier who is popular and recommended.

PeteHeat · 22-04-2013 9:17pm

Brainy Smurf wrote: »

Hi guys,

I have 2 major problems with downdrafts in 2 rooms.

Room 1
I have a fireplace in a room that I don't use that much at the moment.
When it is windy, there is desperate whistling coming from the room when the door is closed. I assume that this is caused by downdraft.

Would a cowl fix this problem? can anyone recommend someone to install this in the Kilkenny area?

Room 2
In the other room which we always use we have the same problem with whistling but when we have the fire lighting in this room, (and the doors are closed) you can feel the air being sucked in through any gaps around the doors. I assume the fire when lighting in sucking in oxygen from everywhere to burn the fuel but you can really feel the air being sucked into the room. By the way, the room never gets that warm either.
Anything I can do to stop this?

(We do not have a problem with smoke coming into the room hen it is windy.)

Insert Stove
Finally, does anyone have any recommendations for an insert stove (about 6 or 7 KW output). I am not a fan of the look of the free standing stoves even though they would give out a lot more heat.

Any advice welcome.

Check the chimney in room 1 is not doing the same as room 2, what you are describing is more an up draught than a down draught problem.

If the fire was ever used in room 1 you would be getting a smell of soot in the room if the whistling was caused by a down draught.

It is very important to fix the chimney problems before even thinking about a stove.

Stoves do not fix chimney's.
.

sooty_soupy · 24-04-2013 9:55am

Brainy Smurf wrote: »

Hi guys,

I have 2 major problems with downdrafts in 2 rooms.

Room 1
I have a fireplace in a room that I don't use that much at the moment.
When it is windy, there is desperate whistling coming from the room when the door is closed. I assume that this is caused by downdraft.

Would a cowl fix this problem? can anyone recommend someone to install this in the Kilkenny area?

Room 2
In the other room which we always use we have the same problem with whistling but when we have the fire lighting in this room, (and the doors are closed) you can feel the air being sucked in through any gaps around the doors. I assume the fire when lighting in sucking in oxygen from everywhere to burn the fuel but you can really feel the air being sucked into the room. By the way, the room never gets that warm either.
Anything I can do to stop this?

(We do not have a problem with smoke coming into the room hen it is windy.)

Insert Stove
Finally, does anyone have any recommendations for an insert stove (about 6 or 7 KW output). I am not a fan of the look of the free standing stoves even though they would give out a lot more heat.

Any advice welcome.

The air noise you can hear is caused by the flue system needing about 60m3 of air per hour to cause a draught. Remember that smoke does not go up the flue by itself, but on a column of air that needs to be replenished. This is why baxi fires were very popular in their day as a lot of the air they needed was ducted to the ash pan area. If you are not looking to spend a lot of money, then a chimney balloon will help. Just remember that a chimney balloon or similar will reduce air movement completely, and in turn any drying of the chimney will be stopped, so it is important to stop damp coming in at the top of the chimney. We would normally fit a rain cap and cage combined to allow the chimney to breath and allow you still to light the fire if you wanted, but also put up a piece of 2" diameter plastic pipe into the fireplace, so you haven't stopped the air completely, just reduced the volume, then you shouldn't get the damp and condensation issues in the flue.

As for a stove, anything bigger than 5kw and you will have to put a vent in the wall, which will lead to draughts, unless the stove can have the air ducted directly to it, and not many inset stoves do. The stoves only need 20m3 of air so they will help overcome the issue you have. Look for an inset stove that has a convection system incorporated, and you will get the same heat as a radiant free standing. It is a misconception that you get more heat from a free standing stove, in comparison to a GOOD inset. The Clearview Inset stove for example or the Stovax Riva 40 would be worth looking at. The Riva 55 is more of a problem as it is 8kw as someone else has already said, and you would have to provide additional ventilation in the room, which is a step backwards, especially as this is what you are trying to avoid. The Clearview is 5kw, and is an impressive piece of kit….even if I do say so myself.

sooty_soupy · 24-04-2013 10:07am

luap_42 wrote: »

If you are not using this fireplace, then either get a chimney balloon or make one yourself. Basically something that will fill the flue and stop wind coming down into the room. Just make sure you have a wall or window vent in that room. If you are occassionally using the fireplace, then a chimney damper will do the job as it can be shut, or opened to whatever amount is required for your fire when lit. You can buy a cowl that will close off the pot completely, or one to divert some of the breeze away from blowing down the flue, but they are not cheap and require someone to go up on your roof to install.

A chimney damper will slow down the updraught, and reduce breeze being dragged under the doors. These are usually sold including installation and are only suitable for open fireplaces. You can insulate the bottom of the doors with a door draught flap which will reduce the gap and slow down the cold air coming in. Again make sure you have a wall vent or window vents to ensure you have some ventilation in the room.

I have a Stovax Riva 55 which is excellent. The maximum heat output is 8KW. If you put an insert stove into the room with the updraught and whistling you will gain more control over the air used/fuel burned, and may also solve the draught/whistling problems, but you will still need to draughtproof the gaps beneath the doors of the room. To get a good quality insert stove you should contact a stove supplier who is popular and recommended.

Just for reference, the Riva 55 is an 8kw stove, and it is mandatory by manufacturers instructions and building regs to ensure there is sufficient combustion air being fed to the room. (BTW the parts for a Riva are obscenely priced. the 2 part baffle assemble was over £200) Under NO circumstances are trickle vents in windows sufficient, as these are closable. It is a requirement that the ventilation in uncontrollable by the end user for obvious reasons of forgetting to open them.

Remember that a combustion appliance needs oxygen to burn. CO2 is Carbon Dioxide, a gas that is the result of COMPLETE combustion. it has TWO parts of oxygen. CO or Carbon Monoxide has only ONE part oxygen and is the deadly silent killer. It is foolhardy to DRAUGHTPROOF your home with a stove, boiler or gas fire UNLESS the appliance has a direct air feed from outside. The Baxi open fire started this concept years ago, and the first stove to have the system was the Clearview range from what I can determine, which is why the brand is sought after in many new builds with high levels of insulation and air tightness.

Hope this helps.

John_DON · 22-05-2013 8:04pm

$5212d3727af1d36b39b176f802b63361.png$
I have a Riva 55 inset stove which smokes back into the room during refueling. I fitted a windkat cowl which helped somewhat but has not fixed the problem completely.
I was wondering if adding extra height or adding a chimney liner would help alleviate my problem.
I used the formula for Flue-gas flow-rate induced by the draft shown above and it would appear as though changing to a flue liner should in theory have the most impact. Decreasing from a standard 8 inch clay liner to a 6 inch stainless steel liner increases flue gas flow rate from 4.9 cubic meters per second to 11.5 cubic meters per second whereas increasing chimney height by a meter only increases the flow rate to 5.4.
This is all fine in theory. Does anyone have any practical experience that backs up the theory? Will installing a stainless steel liner sort my problem? If anyone could offer any advice I would really appreciate it. Thanks

sooty_soupy · 22-05-2013 10:26pm

John, if you have a Riva 55, it is a Stovax cassette stove. The fact that you don't have a steel liner means that you have the potential risk of soot and combustible build up ON THE STOVE. It is hard to understand why people do this, but is all too often the case. Box movers in the industry will often claim it is not a requirement to fit a flexible steel flue, in the hope to sell just the stove. In building regulations, it is considered a requirement to "reduce the diameter of the flue to suit the appliance intended, as the wrong size of flue can be unsafe"

On this basis you have already answered the question, which is increasing flow of gasses through the flue, but here is the science. A good quality stove is designed to burn slowly and under control. Based on this, the flue gas temperature (FGT) will be considerably lower than that of an open fire. To encourage the FGT to remain warm, the steel sleeve through the entire length of the flue, with a backfill of insulation will help reduce build up on condensates and soot products. Condensate is the correct term for the build up of materials in the chimney, which gets it's name from condensation. Burning fuel with moisture generates vapours in the firebox, but this will reach dew point before it is lifted through the entire run of the chimney, especially when the stove is running slow. When you first light the stove, you will burn the unit quickly for about 5 minutes to get the fuel established. This will heat the steel flue, and the insulation keeps the temperature stable once turned down.

I trust this helps.

David

John_DON · 23-05-2013 9:55pm

Hi David I really appreciate you getting back to me. I will have a liner installed and hopefully it should resolve my issues with smoke coming back into the room. The theory and your experience suggest that having a smaller flue will speed up the flue draft and resolve this problem. I will update this thread with the results once the work is done. Thanks Again. John

luap_42 · 27-05-2013 2:17pm

Hi John, regarding the backdraught when refuelling.

Do you open the stove door slowly? If you open the door quickly it pulls the gas inside the stove box out into the room usually filled with smoke and ash.

Do you close the stoves main air control before opening the door? If you close the main stove air control down before opening the door, then the activity inside the stove box is calmer also.

If you do both of these together it will help stop large puffs of smoke and ash bellowing out into the room.

I use an aerocowl, but had a different problem to you. I was trying to reduce an updraught. I had a flexible steel liner fitted with vermiculite filled into the gap between it and the clay pots when installing the stove. The updraught I first encountered was unbelievable, like a giant vaccuum cleaner. It was burning fuel twice as fast as it should have and I could not shut it down at all. By changing the cowl to an aerocowl it is controllable and I can still get a mighty blaze going.

Downdraught prevention chimney cowls

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