Downdraught prevention chimney cowls

Brainy Smurf

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

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

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

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

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

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

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

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

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

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.

John_DON

Hi Luap_42,
Yes I have tried cracking the door slowly but I still get a good puff of smoke and ash coming into the room. I have experimented with air controls open and closed before refueling (as I have read contradictory opinions on the best position for these) but I still get smoke in the room. I have also tried opening a window in the room during refueling and when starting the fire to no avail.
When the door is closed there is excellent draft and I get a good fire with heat that is very controllable using the primary and secondary air controls.
At the moment there is a one meter section of stainless steel 5 inch flue connected to the top of the stove as far a soot door. At the soot door the installer built up the areas around the pipe with fire cement so the flue width is widened from 5 inches to 8 inches. This is one of the installation options shown in the Stovex installation manual.
I am hopeing that I can join the flexible flue liner to the one meter section of stainless steel pipe at the soot door. The only problem with this is that I do not have a register plate to stop the vermiculate resting on the stove top. This is not recommended in the Stovax installation manual even though I have spoken to one or two installers who allow the vermiculite all the way down the existing chimney and onto the stove top.
Narrowing the flue should in theory improve the draught. I am hoping that with the improved draught that the flue gasses with be drawn up the chimney and not back into the room.

Robbie.G

John_DON wrote: »

Hi Luap_42,
Yes I have tried cracking the door slowly but I still get a good puff of smoke and ash coming into the room. I have experimented with air controls open and closed before refueling (as I have read contradictory opinions on the best position for these) but I still get smoke in the room. I have also tried opening a window in the room during refueling and when starting the fire to no avail.
When the door is closed there is excellent draft and I get a good fire with heat that is very controllable using the primary and secondary air controls.
At the moment there is a one meter section of stainless steel 5 inch flue connected to the top of the stove as far a soot door. At the soot door the installer built up the areas around the pipe with fire cement so the flue width is widened from 5 inches to 8 inches. This is one of the installation options shown in the Stovex installation manual.
I am hopeing that I can join the flexible flue liner to the one meter section of stainless steel pipe at the soot door. The only problem with this is that I do not have a register plate to stop the vermiculate resting on the stove top. This is not recommended in the Stovax installation manual even though I have spoken to one or two installers who allow the vermiculite all the way down the existing chimney and onto the stove top.
Narrowing the flue should in theory improve the draught. I am hoping that with the improved draught that the flue gasses with be drawn up the chimney and not back into the room.

The only thing there if you intend to put in a flexi liner it must be a min of 6in you can get a 5-6 adaptor to join up to your connecting flue pipe

luap_42

Hi John, it sounds like you have the problem one of my neighbours has. He solved it by installing a H-cowl on his chimney. Its strange since his identical house is also in the middle of the row of houses parallel to mine. The prevailing wind is the same in both cases, yet he had excessive downdraught problems and I had excessive updraughts. Just goes to show how every house varies due to local wind channels and eddies.

dwiseman

Spindance7 wrote: »

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.

The windkat is very good but will not sort out all down draught problems. We have one on the main chimney of the house and this sorted the problem there however we had the same problem with a new stove with an external flue to the rear of the house and the windkat made no difference. In the end we fitted an electric cowl to solve that one. At over €500 for a windkat I wouldn't be telling people it's sure to work, as it's not.

shamrock55

Ok we had a stove put in last year, when it is lit it takes awhile to get going, the dampers have to be opened for it to burn at all and even then it isnt great, im constantly feeding coal and blocks into it,when its not lighting i can feel a slight breeze coming down when i open the door so im presuming its a down draft problem, now i must admit there is no cowel on the chimney at the moment,when we got the stove fitted last year we had a cowel fitted i think it was a chinese hat one but that fell off and into the river behind us last winter(must have been fitted well) so im just asking does this sound like a downdraft problem and should a downdraft cowel sort it
one other thing when its lit no smoke seems to come back down or anything there just doesnt seem to be any great heat coming from it

PeteHeat

First impression is you have described a stove starved of the amount of air required to burn properly.

What permanent ventilation is there in the room?

Reading further, it might be that you are allowing too much heat escape up the chimney.

A down draught would have smoke pouring out into the room, doesn't have to be all the time as it often depends on wind direction, from your description you don't have a problem.

Perhaps the chimney needs a good cleaning, or the flue is too big, or if your stove is a boiler model it may need an intensive cleaning between the baffles.

shamrock55

We had it cleaned last winter, the heat coming from it was much better when we had the cowel on lt last winter can i ask what the baffles are as it is a boiler stove, when you say the heat seems to be escaping up the chimney sounds right, what would stop this, i think i need a cowel anyway at least but which type?

PeteHeat

Depending on the make / model the baffles can be the part where the heat / flame / smoke circulates around the boiler before entering the chimney.

I doubt you need a cowl, a Chinaman's hat to prevent rain from entering the flue is a good idea as the flue gas (smoke) temperature from a stove should be a fraction of the usual temperature from an open fire due to the stove efficiency, the lower temperature means there is less heat at the top of the chimney to dry out the rain as it falls causing the rain to get further into the flue than usual often causing creosote etc to build up in the flue much faster than with an open fire.

One of the reasons why most reputable stove manufacturers recommend cleaning the chimney / flue twice a year.

I think your problem may be the boiler is soaking up the heat to distribute to the radiators especially in the colder weather as the return temperature from the radiators to the stove is lower than in milder weather, this would cause the heat output to the room the stove is in to be lower than normal or less than you expected.

The colder weather can also cause the other rooms to be a little colder which has you feeding the stove with more fuel than normal, a bit like the old saying, running faster to stay in the same place.

As I believe you don't need a cowl there is no point in going through different makes and models however if you feel you must fit one I would recommend a "H" cowl, this will not cause a stronger up draught but it will prevent most down draughts.

I hope the above is of some help.
.

shamrock55

Cheers for that pete;)

Crazy Eye

PeteHeat wrote: »

Depending on the make / model the baffles can be the part where the heat / flame / smoke circulates around the boiler before entering the chimney.

I doubt you need a cowl, a Chinaman's hat to prevent rain from entering the flue is a good idea as the flue gas (smoke) temperature from a stove should be a fraction of the usual temperature from an open fire due to the stove efficiency, the lower temperature means there is less heat at the top of the chimney to dry out the rain as it falls causing the rain to get further into the flue than usual often causing creosote etc to build up in the flue much faster than with an open fire.

One of the reasons why most reputable stove manufacturers recommend cleaning the chimney / flue twice a year.

I think your problem may be the boiler is soaking up the heat to distribute to the radiators especially in the colder weather as the return temperature from the radiators to the stove is lower than in milder weather, this would cause the heat output to the room the stove is in to be lower than normal or less than you expected.

The colder weather can also cause the other rooms to be a little colder which has you feeding the stove with more fuel than normal, a bit like the old saying, running faster to stay in the same place.

As I believe you don't need a cowl there is no point in going through different makes and models however if you feel you must fit one I would recommend a "H" cowl, this will not cause a stronger up draught but it will prevent most down draughts.

I hope the above is of some help.
.

how much should a h cowl cost , one that will fit a flexi liner and to the clay pot aswell ? you know anywhere that sells them ?

PeteHeat

I expect the cowl would need to be custom made to suit a flexi liner and clay pot, maybe a twin wall section a the bottom.

The inner section to go into the liner and the outer one to dress over the clay pot.

We get any custom pieces like that made in Belfast.

I am guessing at the cost but would expect to pay in the region of 180 > 200 euro.

A problem with custom pieces is they can't be returned or subject to any warranties except for the workmanship.
.

Crazy Eye

PeteHeat wrote: »

I expect the cowl would need to be custom made to suit a flexi liner and clay pot, maybe a twin wall section a the bottom.

The inner section to go into the liner and the outer one to dress over the clay pot.

We get any custom pieces like that made in Belfast.

I am guessing at the cost but would expect to pay in the region of 180 > 200 euro.

A problem with custom pieces is they can't be returned or subject to any warranties except for the workmanship.
.

thanks shame they dont do them off the shelf

Caher123

Hi,

Hoping someone may offer some advice!

I have a Downdraught from my stove fitted in a chimney in my sunroom. The chimney extends the ridge of the sunroom roof but does not meet the roof of the two storey part of the house. I believe this is probably my issue. Would a chimney extension flue help? How high can I go with one? Or should I get a cowl?

The room the stove is fitted in has 4 windows each fitted with trickle vents. It's open plan to a large Kitchen with another large trickle vent and cooker extractor fan. I've been told that ventilation is sometimes the cause of a Downdraught. I'm very reluctant to drill a wall vent. Do you think this is enough ventilation for a stove?

So confused now what is the best option for proceeding. Any advice? Thanks in advance!

sbkenn

You could install a blower for the chimney. This would need to be a centrigugal blower rather than an axial fan (pressure rather than volume), and blow air into the flue through a 1" pipe to create a venturi. You would probably find that it is only needed with certain wind directions, and even then, only until the fire gets going properly.

Robbie.G

Caher123 wrote: »

Hi,

Hoping someone may offer some advice!

I have a Downdraught from my stove fitted in a chimney in my sunroom. The chimney extends the ridge of the sunroom roof but does not meet the roof of the two storey part of the house. I believe this is probably my issue. Would a chimney extension flue help? How high can I go with one? Or should I get a cowl?

The room the stove is fitted in has 4 windows each fitted with trickle vents. It's open plan to a large Kitchen with another large trickle vent and cooker extractor fan. I've been told that ventilation is sometimes the cause of a Downdraught. I'm very reluctant to drill a wall vent. Do you think this is enough ventilation for a stove?

So confused now what is the best option for proceeding. Any advice? Thanks in advance!

As you know yourself your flue is wrong.
Best option is to try and extend it an other mtr or so will make a difference.
The stove needs permanent ventilation full stop the effects of the extractor fan has to be taken into account and must be made up for.
Did you try opening a window or door when stoves lit to see if it makes a difference if so extra air is needed

Caher123

Thanks. Yes last winter we tried opening the window. Sometimes it helped a bit but on very windy days it didn't make a difference. The height is the main issue as it only occurs when the wind blows a certain way. Have heard the chimney extension flues can get blown around in the wind so we may try a H cowl first and go from there...

Thanks for replying

Sacksian

Here’s a downdraught / updraught problem that I would like the experts’ views on!

We live in a victorian terrace house and had our chimney lined last year (one sweep said they didn’t work on unlined chimneys). The next time we tried a small fire, our neighbour complained that there was a smell of smoke coming from their chimney.

The guys who lined the chimney came out and did a basic smoke test just to see if smoke was exiting the chimney properly, which it was. His theory was that it was the specific atmospheric conditions (it was a very still cold evening), and the degree of ventilation in the room with their fireplace, that had given rise to the neighbour’s issue.

We left it for a while and then tried again. With the same result.

We had never had a complaint from the neighbour before we got our chimney lined, regardless of the conditions. We also never smell smoke coming from their chimney, either before or after getting our chimney lined.

This means that, if us having the liner created the problem, we can’t ever light a fire without smoking out our neighbour, unless they too got their chimney lined (which they might not be able to afford to do).

I recently had an independent sweep in to do a camera survey of the liner and chimney and his view was that the chimney and liner were in good condition and fitted properly. However, he noted that we had a chimney cowl and the neighbour didn’t and that could be impeding the escape of smoke, leading it to be drawn back down our neighbour’s flue under certain conditions. For some reason, I hadn’t noticed that the cowl had been put on the same time as the new liner was fitted.

Before I get the cowl removed, my question is: how likely is it that the addition of a cowl could cause this problem? It seems like the most likely explanation.

Or could the installation of a liner in one flue be the cause? (In which case, we're a bit screwed).

crock!

When you use your chimney the liner gets warm and draws smoke out.your neighbour doesn't use there fire and it has a cold liner and can suck smoke down into the room.ive seen this lots of times.raise your chimney pot with another liner and put a rain hood onto your neighbours.an other way to check this is to heat up your neighbours chimney before you light your fire .