Downdraught prevention chimney cowls

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.

Downdraught prevention chimney cowls

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