Downdraught prevention chimney cowls

ttm

Omron1 wrote: »

Hi ttm & sooty soupy,
Thanks for the responses. ttm I don't see any evidence of a chimney fire and prior to us buying the house it was used mostly as a holiday home so the fires would not have been used much I would guess and we got both chimneys swept when we moved in. Is there anything other than getting a camera survey done that can confirm your suspicions.
Sooty soupy since my last post I have been speaking to a neighbour up the road who had a similar problem with smoke coming down the chimney and he cut one of the flue pots down to the chimney cap and it solved the problem. I have checked and the chimney pots on the top of my chimney are both approximately 60cm from the chimney cap so if I cut one pot down by half would you think this should be a sufficient offset of the pots.

Thanks again for your posts.

If theres no sign of a past chimney fire and its not been used much, on a newer house then don't take too much notice of what I said. I'm used to living in 200yo houses/cottages with all sorts of previous chimney disasters often from tenants that would have a chimney fire as soon as sweep the chimney.

I'm sure sooty soupy has the answer here, but I'd check how the air is getting to the used fire. If both rooms are well sealed from the outside its always possible the only place that fresh air can come into the house is down the unused chimney. Another one of my extreme theories but if you've had double glazing put in and sealed everything up on a house with no room vents its vaguely possible.

I'm not sure I'd want to cut a chimney pot down by half? I think I'd prefer to add on a new taller pot?

If you ever want to inspect something, pipe or chimney its quite easy to rig up a cheap USB camera on a 4m USB cable and tie it on the end of a drain/sweep rod to take a look at whats going on. 4m is about the limit of the USB cable length without buying a fancy cable. A laptop obviously better as you can easily get it near to the base of the chimney and you may need a second pair of hands to hod the rods and a tourch (up chimney) while you check the picture.

sooty_soupy

I too would avoid cutting the chimney pot to be honest. It is so much easier to take off the old pot serving the live applaince and replace it with a taller one.

Air starvation is very much a problem with chimneys in the modern home, as ttf has said, however I feel that air starvation is more a problem with a lack of negative pressure rather than positive. If I was a betting man...but I'm not as my old man is a bookmaker and he is never short of money funnily enough, I would say siphonage is more than likely the issue. Another way to temporarily determine if it is the long term solution to raise the pot, would be a very big jubilee clip, and a sheet of thin aluminium or stainless steel. Wrap the sheet steel around the pot and secure it with the jubilee clip and see if it helps.

As far as the CCTV inspection is concerned, I would imagine the idea of USB cameras might work, but it seems a lot of hassle for an imperfect view of the flue. A CCTV inspection would probably cost less than what is being proposed, unless you have the gear already. A crack in the flue will only give problems if the chimney is blocked. I would be inclined to sort out the chimney heights and see how things perform. If you still get smoke, then look at a proper survey on the chimney with a view to flue lining. We have a system that coats the chimney with a resin based ceramic which will seal any cracks should it be the case, but I don't believe this is your problem.

Best regards

David

PeteHeat

Hi,

Cutting a pot in place can be both dangerous and counter productive as you may end up with a pot that is not straight and it can catch wind causing a real downdraught.

I suggest go the opposite way, get a piece of stainless steel and add to the height of one of the flues.

That said your problem may be added to by the trees surrounding the property or even the angle (pitch) of the roof.

Trying to diagnose a problem without seeing it seeing it can be very difficult, it is also possible to be sending the person in the wrong direction.

Looks like we both posted at the same time and appear to be in general agreement.

.

mad m

I want to block off a fireplace altogether, whats the best way to do this up top? I dont want to put a vent where fireplace was either....Cut a template in ply and shove down cowl and fill in with sand&cement??

ttm

NO if your blocking off a chimney you really need to keep it open at the top and bottom even if you do cap off the top you can get vented plugs and brick up the bottom were you put in at least an air brick. You should keep an air flow through the old chimeny.

Fill it in and you could get all sorts of damp problems.

PeteHeat

Hi mad m,

I'm in full agreement with ttm you can get a vented cap for the chimney pot and fit a vent in the skirting board.

It doesn't have to intrude on any decorating plans you may have for the room.

.

mad m

PeteHeat wrote: »

Hi mad m,

I'm in full agreement with ttm you can get a vented cap for the chimney pot and fit a vent in the skirting board.

It doesn't have to intrude on any decorating plans you may have for the room.

.

I know what your saying and in theory dampness could happen but in practice would it happen....What would be the long term problems...

ttm

mad m wrote: »

I know what your saying and in theory dampness could happen but in practice would it happen....What would be the long term problems...

Firstly the house was designed with the chimney so part (if not all) of the ventilation of that room is via the chimney.

If you block it then any moisture from the chimney stack will sit there and eventually build up and have to come out somewhere. Any blocking up is likely to channel the water in a way you'll have no control over if damp does become a problem. Its also likely that floor and roof timbers are supported by parts of the chimney and you don't really want dry rot in those. Even if you were to remove the top of the stack and roof it over I'd still vent it to the roof space and put a vent in the room as a matter of good practice.

I can't really see any point in going to the effort of filling up an old chimney if you dont need to. At most all it needs is the pot taking off if its loose and replacing with a vented cap plus pointing up. Inside block off the old fire place any way you like just pop in a air brick sized vent somewhere. Theres no need for a howling gale to have to go up the chimney just a flow of air.

Is there some reason for wanting to block it off completely?

mad m

Ah i wasnt hypothetically speaking, bought house over 10years ago,one open fireplace in front room and there was one in back room and now its only dawning on me there's no vent where fireplace was. Not upstairs either or in attic......Could it be possible that that the other fireplace in front is venting the other one in some way?

ttm

mad m wrote: »

Ah i wasnt hypothetically speaking, bought house over 10years ago,one open fireplace in front room and there was one in back room and now its only dawning on me there's no vent where fireplace was. Not upstairs either or in attic......Could it be possible that that the other fireplace in front is venting the other one in some way?

Just as I wouldn't be rushing to fill a chimney with concrete neither would I rush to unblock one and fit vents.

If they are in the same stack then the air going up the open chimney will help stop the stack retaining to much damp. So if you've had no problems so far I wouldn't worry.

My guess is that you chimney isn't blocked up completely just capped off and in many cases no will have bothered to even go on the roof let a lone climb up with bucket loads of a cement mix. If the location of the original fireplace is still obvious then you can see if you can drill a long thin hole through into it (10mm SDS?) to see whats the other side and if there is any air movement into or out of the hole (hold up a match or candle - incense sticks are good) if there is an air flow you could simpley drill a matrix of holes and put a screw on vent facia over it to cover it up.

I'd be more worried about not having a ventilation through an unused chimney on an old house with no DPC or a poor DPC as in that case the ventilation really could be doing some good keeping damp at bay.

And don't forget having been challenged I was making a point in my previous post

mad m

No different stacks on top of house. Had roofers check out chimney when I was getting extension to see if it was ok. Not blocked up top. Guess I'll get a 10mm long drill bit so...Thanks...

ttm

mad m wrote: »

No different stacks on top of house. Had roofers check out chimney when I was getting extension to see if it was ok. Not blocked up top. Guess I'll get a 10mm long drill bit so...Thanks...

Might have the wrong nomenclature when I said "stacks" as what I meant was the brickwork that supported the chimneys were the two chimneys supported by the same brickwork or were they seperate? Any size long drill bit will do I just happen to have a couple of 10mm hilti ones that I use for everything. You could also try lower down on the skirting board if that would be more convienitent just at that point the brickwork might be thicker, still best place for a vent.

loup

hi everyone, have a problem also with smoke coming into the room when fire is lit and the weather is windy (tonight). We are end of terrace so presumably this is why as we are the last chimney pot in the row! We already have a cowl to stop birds getting down chimney so what would we need to get fitted..a rotating cowl? Thanks!!

miltown britton

i own a stove with a boiler and the glass smokes up severly also when the doors are opened the smoke comes out and sets off the smoke alarm, its at its worst when the weather is calm, the flue comes out at the back horizontally for one foot approx and goes up in a 45 degree angle and sits within an existing straight up flue lined chimney for 4 feet, the chimney and stove are regularly cleaned and maintained properly, when there was an ordinary fire there , there was no problem with smoke coming down, there seemed to be a good draw. The stove was installed by a certified plumber and i have asked numberous people but haven't been able to solve the problem, when the wind is high the stove works well with only a small amount of smoke on the glass and is easier to refuel. Any suggestions?

ttm

miltown britton wrote: »

i own a stove with a boiler and the glass smokes up severly also when the doors are opened the smoke comes out and sets off the smoke alarm, its at its worst when the weather is calm, the flue comes out at the back horizontally for one foot approx and goes up in a 45 degree angle and sits within an existing straight up flue lined chimney for 4 feet, the chimney and stove are regularly cleaned and maintained properly, when there was an ordinary fire there , there was no problem with smoke coming down, there seemed to be a good draw. The stove was installed by a certified plumber and i have asked numberous people but haven't been able to solve the problem, when the wind is high the stove works well with only a small amount of smoke on the glass and is easier to refuel. Any suggestions?

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.

miltown britton

hi yeah,thanks for your reply,i check and clean that pipe on a regular basis,it does help a little,but thats all,i have checked all the pipes at the rear stove for air leaks and put fire cement around all joints to be extra cautious,any other suggestions,thanks

ttm

miltown britton wrote: »

hi yeah,thanks for your reply,i check and clean that pipe on a regular basis,it does help a little,but thats all,i have checked all the pipes at the rear stove for air leaks and put fire cement around all joints to be extra cautious,any other suggestions,thanks

Not a lot more I can say, if you can I'd experiment a bit and try putting another pipe section up the chimney to see if that helps other than that I'm sure others would say the only way would be to line it but I'm not sure it that would fully solve the problem?

What stove is it?

Edit> Another question what are the flue sizes? Its not always a good idea to go straight from the stove in a flue size bigger than the stove outlet.

googled eyes

Hi all , sorry if I'm asking a question again but I'm only coming onto this thread today .
My problem is that I have two chimneys in the one stack , my living room and the front bedroom ( typical Dublin Corpo house ) and when I light a fire downstairs the smoke is pulled by a down draught into the bedroom. I have to open the window which seems to right the down draught problem ?

Would one of these spinning cowls put onto the bedroom chimney pot fix my problem or will i have to drill a vent hole in the external wall of the bedroom (which i dont fancy doing as its gonna mean a cold bedroom )

NutleyAFC

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.

loup

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.

I was just coming on to say that eddie4 (above posts) is great, he came out and fitted a cowl to our chimney last week and really knows his stuff! PLus he was reasonably priced too..I would contact him and see if he can help you?

ttm

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

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

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

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

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

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

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

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

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

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.