windy day downdrafts

[farmer_luke]

I'm hoping someone can enlighten me on what's going on with two different situations where I experience downdrafts with wood stoves.
The picture on the left is my parents' house. They have a wood stove on their main floor and a class A pipe that is on the East side of their gable roof. The top of the pipe is below the roof ridge, I'd guess by 2 or 3 feet. It has been this way for about 40 years. They have always had downdraft issues when there is an East wind (blowing East to West).
The house I live in had a hip roof with an unlined masonry chimney. There was a wood stove in the basement and one on the main floor, both using the unlined chimney. We never had any downdraft issues and the draw was fine, maybe too strong on windy days. We recently added on a gable roofed addition to the north and since then have consistently had downdraft problems with a South wind. No way to have a fire in either stove with a strong south wind. Also can smell the chimney in the summer with a strong South wind.

To get up to code we had an insulated liner installed in the chimeny for the basement stove and moved the main floor stove across the room and had a class A pipe run up through the roof. The basement stove got done first. I noticed a downdraft in it after the liner installation but wasn't too worried since we don't burn the basement stove that frequently. Decided to not have a fire in the basement if there was going to be a South wind. The main floor stove and pipe recently got installed and we tried to have a fire with a South wind and filled the house with smoke. The stove had been burned the previous couple of days and was still warm this morning but when I added wood I couldn't overcome the downdraft.

I've expressed my uneducated opinion to the installer that it seems like the downdraft is being caused by the wind hitting the roof peak, swirling in a circle, and going down the chimney/pipe. This seems to be the situation at both my house with a South wind and my parents' with an East wind.
I've talked with the installer and he believes there is something else going on. That there must be something with the house causing a negative pressure. We turned off our furnace and checked bathroom exhaust fans. Also tried opening a door and burning the fire. Same situation: downdraft.

The new class A pipe at my place is close to the same height as the addition ridge. I plan to have this extended and bet the issue with that stove will go away but I'm curious if others have had experiences like this?

 

[begreen]

There are several articles on chimneys here including a good write-up on chimneys and how they are affected by the wind and roof location.

A non-commercial service in support of responsible home heating with wood - How Wind Affects Chimney Performance

The Wood Heat Organization was formed to support the public in the responsible use of wood energy in the home. We fulfill our mandate by providing reliable information, by conducting research into wood heating-related issues and by representing the public interest in discussions of policies that...

woodheat.org

The negative pressure issue in the basement installs may be due to other causes. Some of the other chimney articles on the Wood Heat site may be helpful too.

 

[farmer_luke]

Thanks, I had looked around online and didn't come up with much.

 

[farmer_luke]

There are several articles on chimneys here including a good write-up on chimneys and how they are affected by the wind and roof location.

A non-commercial service in support of responsible home heating with wood - How Wind Affects Chimney Performance

The Wood Heat Organization was formed to support the public in the responsible use of wood energy in the home. We fulfill our mandate by providing reliable information, by conducting research into wood heating-related issues and by representing the public interest in discussions of policies that...

woodheat.org

The negative pressure issue in the basement installs may be due to other causes. Some of the other chimney articles on the Wood Heat site may be helpful too.

This is exactly what I was looking for.

I had expressed my experience with downdrafts with the installer repeatedly with our two houses and the wind directions that cause problems but he was adamant that a downdraft shouldn't be caused in those situations. His understdanding was that a North wind at my house should cause the downdraft and a West wind at my parents' could.

 

[farmer_luke]

There are several articles on chimneys here including a good write-up on chimneys and how they are affected by the wind and roof location.

A non-commercial service in support of responsible home heating with wood - How Wind Affects Chimney Performance

The Wood Heat Organization was formed to support the public in the responsible use of wood energy in the home. We fulfill our mandate by providing reliable information, by conducting research into wood heating-related issues and by representing the public interest in discussions of policies that...

woodheat.org

The negative pressure issue in the basement installs may be due to other causes. Some of the other chimney articles on the Wood Heat site may be helpful too.

Thanks. We never had downdrafts before the the addition with the higher-than-chimney peak and we only have downdrafts with a South wind. The stronger the wind the stronger the downdraft. When we were doing the addition I had asked the contractor if he thought we'd have problems and he said no because the chimney is so far from the addition's peak (maybe 20-25 feet). And the installer of the new class A pipe for the main-floor stove said it should be ok that the top of the pipe isn't over the peak because it's about 10' away from the addition's peak. I think extending the class A pipe above the positive pressure zone created by the addition's peak will solve that issue. Not sure if I want to address the same issue with the masonry chimney liner though since that would require adding to the masonry chimney and we rarely use the basement stove.

 

[farmer_luke]

I talked to the installer and he came and we installed another 3' section of class A pipe. We are definitely above the highest peak of the house now and the downdraft issue decreased drastically but not completely. Once the fire got going it hasn't back smoked any more but what will happen when the fire goes out? We're supposed to have 3 days and nights of strong South winds. If the fire goes out in the night with the wind blowing are we going to be choking on smoke and other potentially dangerous gasses?

We have 18' of class A on the roof and about another 4' of single wall below that. The installer is baffled. He thinks we have some other negative pressure issue. I wonder if we're still not quite high enough above the peak? The one issue I could maybe see with negative pressure is that we have more windows on the North side of our house than on the South side. Maybe we are getting negative inside pressure with a South wind because of the extra windows?

Edited to say: Sorry, there's not 18' of class A on the roof. There was 6' on the roof, now there's 9'. There's an additional 12' of class A in the attic and 4' of single wall below that. Honestly, that seems like too much in the attic. I don't think our attic is that tall but the installer said they did 18' of class A originally so I'm just going with that

 

[EbS-P]

Kansas wind is not something everyone experiences. The interior of house can definitely be turned into a negative pressure zone. Water get sucked out of the toilets on windy days. (Bernoulli and the vent pipe). Same thing can happen with house envelope. Fast air over top or around the sides makes it a low pressure zone inside. So it just not happening outside.

I would definitely have a carbon monoxide detector. Near the stove.

Windy day remedies? I might look into an ERV that could be biased to hep pressurize the house. It’s better than opening a window. Do you keep the basement sealed off ie door closed. maybe allowing more air up from the basement might help??? How well ventilated is the attic? Where are the the exhaust vents terminated? Could they be contributing to the negative pressure inside.

Based on what you have said the addition caused it and adding height helped. Is it reasoning add another section?

Longer term consider planting a wind break or adding to one of you already have one.

Our house I grew up in on the Ks/co border had beautiful pink sandstone fireplace. I never once saw a fire in it. It filled the house with smoke every time it was used I was told. We moved and my uncle moved in and installed a pellet insert. Never had a problem with that. Burned corn when it was cheaper than pellets.

 

[farmer_luke]

Kansas wind is not something everyone experiences. The interior of house can definitely be turned into a negative pressure zone. Water get sucked out of the toilets on windy days. (Bernoulli and the vent pipe). Same thing can happen with house envelope. Fast air over top or around the sides makes it a low pressure zone inside. So it just not happening outside.

I would definitely have a carbon monoxide detector. Near the stove.

Windy day remedies? I might look into an ERV that could be biased to hep pressurize the house. It’s better than opening a window. Do you keep the basement sealed off ie door closed. maybe allowing more air up from the basement might help??? How well ventilated is the attic? Where are the the exhaust vents terminated? Could they be contributing to the negative pressure inside.

Based on what you have said the addition caused it and adding height helped. Is it reasoning add another section?

Longer term consider planting a wind break or adding to one of you already have one.

Our house I grew up in on the Ks/co border had beautiful pink sandstone fireplace. I never once saw a fire in it. It filled the house with smoke every time it was used I was told. We moved and my uncle moved in and installed a pellet insert. Never had a problem with that. Burned corn when it was cheaper than pellets.

Appreciate the reply.

We are out in the country and wind here in western KS can be intense.
I'm trying to learn lots. The other site mentioned talks about stack effect but doesn't go into depth explaining it so I need to research that more to fully understand that aspect. It's amazing and frustrating that before we added on we were exhausting two wood stoves on different levels into an unlined masonry chimney and it worked great...for many years. Yes, the addition, with its higher roof (and possibly additional windows?) was the start of our downdraft woes.

I'm not familiar with an ERV. Will have to look that up.

Is the basement door shut? That depends on the day. If I'm home and trying to work in the basement then I do oftentimes close the door so it's quieter but I'd say it's typically open.

The attic should be well ventilated. The original roof peak has a vented ridge and the new addition peak also has vented ridge. I assume that affords more ventilation than the little attic vents but I don't know.

Could we add more height to the class A. Yes. I'm not especially fond of how it looks now and adding more would only make it uglier. We are currently at (3) 3' pieces of class A on the roof with one band secured with 2 braces. I saw somewhere else that it was recommended to have bracing for every 5' of pipe so I'm assuming if we have 12' of pipe we'll need to add another set of braces?

As far as windbreak we have decently sized cedar/juniper/pine trees immediately South of the house and almost nothing to the North. With the way our yard is and where the barn is to the North there's no great way to have a windbreak to the North except a long ways to the North.

 

[farmer_luke]

A few pictures of our house. The dormer windows are the North side.

 

[begreen]

I'm glad there is progress. Definitely install a CO monitor in the room if there isn't already one. One possible aid that might help is a wind-resistant cap. They are not cheap, however.

Vacu-Stack Chimney Cap for Air Cooled Chimney Pipe | Product Info - Rockford Chimney

Use the Vacu-Stack chimney cap for air cooled chimney pipe. This universal chimney pipe cap helps solve common, wind-related chimney draft problems.

www.rockfordchimneysupply.com

The basement stove may improve behavior with an outside air supply or an ERV that helps equalize the pressure in the basement.

 

[farmer_luke]

I'm glad there is progress. Definitely install a CO monitor in the room if there isn't already one. One possible aid that might help is a wind-resistant cap. They are not cheap, however.

Vacu-Stack Chimney Cap for Air Cooled Chimney Pipe | Product Info - Rockford Chimney

Use the Vacu-Stack chimney cap for air cooled chimney pipe. This universal chimney pipe cap helps solve common, wind-related chimney draft problems.

www.rockfordchimneysupply.com

The basement stove may improve behavior with an outside air supply or an ERV that helps equalize the pressure in the basement.

Thanks, I'll have a look at wind-resistant caps. Is the one above the popular choice or are there other good ones?

I wonder, is the cap copied below the same idea as the vacu-stack cap? I don't really understand how the baffle in the cap below helps stop the downdraft. I would think a cross wind that want to go down the pipe would be aided by a baffle unless each baffle is sloped so the tops are tipped together and the bottom is wider. Otherwise wouldn't the wind hit the baffle and be just as likely to go down as up?
From the woodheat.org site:
A chimney with no cap is the most vulnerable to the adverse effects of wind. A cap, particularly one that has baffles to prevent direct line of sight access to the opening (as opposed to a simple flat rain cap) provides significant protection from the adverse effects of wind. In fact, research has shown that caps with baffles (of the sort common on factory-built chimneys) can actually enhance draft regardless of wind direction.

This kind of cap can take adverse winds and convert them to upward flow in the chimney.The cap shown at right is the type of design common on factory-built
chimneys. Note that the baffle, in the form of a band between the cap and the skirt at the base of the cap, prevents direct access of the wind to the open top of the chimney. This simple design consistently produces a driving pressure at the top of the chimney, regardless of wind direction or speed.

 

[begreen]

That might work, it's worth a try. Ask your stove installer if they have one that they could lend to you as a test. They should also be familiar with wind related draft issues and cap solutions. Another one is the rooster tail style.

Wind Directional Chimney Caps and How They Work | FAMCO

For those with fireplaces, a wind directional chimney cap is designed to promote updraft while preventing downdraft. Keep smoke out, heat in.

www.famcomfg.com

 

[farmer_luke]

That might work, it's worth a try. Ask your stove installer if they have one that they could lend to you as a test. They should also be familiar with wind related draft issues and cap solutions. Another one is the rooster tail style.

Wind Directional Chimney Caps and How They Work | FAMCO

For those with fireplaces, a wind directional chimney cap is designed to promote updraft while preventing downdraft. Keep smoke out, heat in.

www.famcomfg.com

I showed the installer this picture and the woodheat.org link and he didn't think it was applicable at all to my situation.
I asked previously about wind caps and I don't think he had any recommendations or familiarity, unfortunately.

 

[vatmark]

We have had wind issues with our wood stove. We have been in our house almost 5 years and still haven't done anything about it. I just don’t use it when it is really windy which is frustrating. I start to look into what to do and come to a screeching halt. The two things that stop me from doing something is I dont know if making the chimney taller will fix it and if so how high can a metal chimney go before it is too tall to be able to stand freely and not get blown over by wind. Then I look at wind caps and the issue becomes birds building nests in them as well as not being able to clean it properly. We clean our own chimney but from the bottom. Getting on the roof is not an option. Many of the wind caps look like they wouldn’t be able to be cleaned from the bottom. Here are a few of the wind caps I came across but haven’t look into them in detail.

Vacu stack
Draftmaster
Chimcare wind directional
Rockford ridged chimney cap with wind guard
Famco wind directional (already posted above)

 

[farmer_luke]

Last night I started a fire and got up on the roof with a flashlight to try to see what the smoke was doing. With our the strong south wind the smoke was blowing out almost straight sideways to the North. At times I thought it did go down some as it came out and occasionally swirled around somewhat to the South but mostly just straight out North. After that I thought we do need more height but then today I got up on the barn and from that perspective (probably 5-10' lower than the house's peak) I'd l think the class A is high enough. Not sure what to do now.

 

[begreen]

Do a search in this forum, titles only for - wind cap. There will be many threads on solutions that have worked for people.

Do wind caps work?

Does anyone have a wind chimney cap and found it helped? We have a Jotul F500. We wanted to have a fire tonight but we are having strong wind gusts and it was blowing smoke back down the chimney and we were getting wisps of smoke coming out of the stove. My house smells like smoke now. The...

www.hearth.com

 

[farmer_luke]

When I started the fire last night I opened a South window prior to starting and left it open thinking that would help pressurize the house in case that was the problem. There were still little puffs of smoke that came out the stove until the fire really got going and got the flu hot.

 

[Corey]

Sort of hinted at above. But one important consideration is not necessarily wind getting 'in' your existing flue, but the prevailing winds creating drafts which pull air out of the house in other areas, leading to negative pressure in the house which then creates the back draft.

Curious about what appears to be a brick chimney? Is that active or sealed off? It looks to be lower in the pictures, so might be in one of these low pressure zones. Another consideration might be sealing any sort of attic access or attic fan. I remember growing up in houses where strong winds would lift the louvers on the attic fan and sometimes pick up and drop the 'hatch' for the attic access. So either of those could create a low pressure inside the house in the right conditions.

Also consider this is generally 'shoulder season' where draft is going to be a bit hard to generate anyway. Not sure where you are in KS, but generally it's not the real cold winter yet. Though give it a couple days!!

 

[farmer_luke]

Sort of hinted at above. But one important consideration is not necessarily wind getting 'in' your existing flue, but the prevailing winds creating drafts which pull air out of the house in other areas, leading to negative pressure in the house which then creates the back draft.

Curious about what appears to be a brick chimney? Is that active or sealed off? It looks to be lower in the pictures, so might be in one of these low pressure zones. Another consideration might be sealing any sort of attic access or attic fan. I remember growing up in houses where strong winds would lift the louvers on the attic fan and sometimes pick up and drop the 'hatch' for the attic access. So either of those could create a low pressure inside the house in the right conditions.

Also consider this is generally 'shoulder season' where draft is going to be a bit hard to generate anyway. Not sure where you are in KS, but generally it's not the real cold winter yet. Though give it a couple days!!

Yes, I'm considering two scenarios. We never had draft issues before adding on to our house creating a much higher roof to the North of the original house. After the addition we have draft issues whenever there is a South wind. So after seeing the information about positive pressure outside like in this picture I thought that was what's going on. But it seems like our class A pipe is high enough above the highest roof that that shouldn't be the problem. Do we have negative pressure in the house? Again, this kind of makes sense because with the addition we added a bunch of windows to the North side of the house so a South wind might leak out all those windows more than it leaks in the few windows on the South side, but wouldn't opening a South window like I did completely counteract that if that was what's causing the backdraft issue?

The brick chimney is what we used to use for two different wood stoves. One in the basement and one on the main floor. After the addition with the new higher peak we got backdraft issues down that chimney in both stoves with a South wind. The chimney used to be unlined and now there is an insulated liner servicing the basement stove. I think we probably have downdraft issues with that stove with a South wind but we don't use the basement one much and I'm not worried about it at the moment, just trying to figure out the main floor stove with its class A flue.

Our attic has a well sealed access door. I think I'll investigate the upstairs bathroom vent just to make sure there isn't a large amount of air leaking there. We have all new windows that should be pretty good (for how expensive they were) but the contractor who installed them stopped caring at about that stage of our remodel and they definitely do leak more air than they should.

 

[farmer_luke]

I just checked the basement stove and with no fire going it appears to be drafting "properly" about 3/4 of the time and backdrafting 1/4.

 

[EbS-P]

When I started the fire last night I opened a South window prior to starting and left it open thinking that would help pressurize the house in case that was the problem. There were still little puffs of smoke that came out the stove until the fire really got going and got the flu hot.

So was the opening window helpful? Try one one nearest the stove.

Are we taking an average blustery day gusting to 35 mph or a howler with gusts over 50

 

[farmer_luke]

So was the opening window helpful? Try one one nearest the stove.

Are we taking an average blustery day gusting to 35 mph or a howler with gusts over 50

When the installer was here yesterday he had us try opening the door and/or window nearest the stove and I didn't see any difference. My wife said once right when I opened the door the backdraft reversed and the fire flared like it was drafting properly but where that only happened once I don't think it proved much. What's the idea behind opening a window closest to the stove? Are you trying to change the stack effect and get a neutral pressure plane close to the stove? It makes more sense to me to open a South window with a South wind to add pressure to the house faster than it can possibly leak out. We're supposed to get gusts around 50 today but each time I've started a fire it's been lower than that, more like 30 probably.

 

[farmer_luke]

Do a search in this forum, titles only for - wind cap. There will be many threads on solutions that have worked for people.

Do wind caps work?

Does anyone have a wind chimney cap and found it helped? We have a Jotul F500. We wanted to have a fire tonight but we are having strong wind gusts and it was blowing smoke back down the chimney and we were getting wisps of smoke coming out of the stove. My house smells like smoke now. The...

www.hearth.com

Thanks. I read through a bunch of threads on wind caps. Seems like the Vacu-Stack and the wind-directional cap are two of the favorites. The thought of putting a directional one on kind of terrifies me. At some point won't it stop spinning properly at which point it will potentially funnel the wind down the pipe? I imagine a freezing rain or a wet snow with little wind or too much creosote or just wearing out over time. Maybe people have had them for 10 years and no problems? I see that some have had success with the vacu-stack cap and others have extended the pipe. Decisions decisions.

 

[begreen]

Do you know what brand of chimney pipe is installed?

 

[farmer_luke]

Dura-vent