Downdraught prevention chimney cowls

John_DON · 27-05-2013 2:52pm

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 · 27-05-2013 3:09pm

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 · 03-06-2013 2:23am

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 · 20-11-2013 12:43pm

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 · 27-11-2013 1:08am

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 · 27-11-2013 2:00am

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 · 27-11-2013 2:50pm

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 · 27-11-2013 10:48pm

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 · 27-11-2013 11:09pm

Cheers for that pete;)

Crazy Eye · 28-11-2013 12:25am

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 · 28-11-2013 10:08pm

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 · 28-11-2013 10:27pm

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 · 29-09-2014 10:45pm

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 · 29-09-2014 11:12pm

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 · 30-09-2014 10:36am

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 · 01-10-2014 8:18pm

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 · 26-01-2016 3:37pm

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! · 30-01-2016 5:02pm

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 .

Downdraught prevention chimney cowls

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