Wood stoves and a heavy downdraft in the chimney. Ideas?

[Jeff7]

Figured I might as well post here; I don't have all the specifics on the problems - my dad knows more about it than me. But anyway, we've got a wood stove with a pretty bad problem - air prefers to come down the chimney - it is capable of blowing a candle out that's held in front of the stove. We've tried something called the Vacu-stack, but it didn't do a thing. Someone suggested that it might be a pressure problem, that there's not enough air coming in the house. We had a window put in the wall in the same room as the stove (it's in the cellar), and it helps - about one in 5 times we open the stove. Yes, there is an updraft now, but it is minimal. In the house we used to live in, the updraft was so strong that it would nearly blow the fire out.
The smoke still prefers to billow out into the house when the front is opened to put more wood in. The chimney is clear too, that's been checked. The house is warmer than it usually is in the winter, but it's also smells like wood smoke most of the time now.
Do any of the engineer-types here have any ideas? We are considering installing a fan, but of course the problem with that is that it won't work without power - we had a 3-day power outage on Christmas, and the stove was all we had to warm the house, well, half of it anyway. Does anyone have any better suggestions? We're also considering getting a gas stove instead; something like that should be more self-containted, restricting the smoke to the exhaust pipes only; problem is finding a cheap one - too many of the gas stoves on the market are really decorative; this stove is in the cellar. We don't need it to be fancy, it just needs to work.


Update: A little more info on the fun air currents here: one minute the smoke is coming down into the front yard, then suddenly it shifts, and the backyard is flooded. Today when I got home, it was rising straight up out of the chimney; just before I started this update here, it was coming out of the flue, and immediately right down around the chimney. These air currents are REALLY screwed up. We're still looking at the possibility of a gas stove - those things seem like they'd be more sealed and less prone to air currents that defy physics. Our next-door neighbor has a gas stove and he says he's very happy with it.
We're also having a chimney sweep come this Sunday; we'll see what that does.

 

[Dufman]

you probably are going to need a blower fan in the lower part of the chimney. to suck air through it

check out at your local hardware store, they will hook you up

true value

 

[ScrapSilicon]

sounds def like a poorly designed flue ..I'm not anywhere clued on how to rectify any of that..bump 4 ya

 

[Cerebus451]

Do you heat the flue when you light the fire? I always stuff some newspaper up into the flue and light it just as I light the fire. The burning newspaper in the flue will heat the air in the flue and should create an updraft, then the fire in the stove should keep the updraft going. Not sure if that will work in your case or not. I don't think I've ever noticed a downdraft strong enough to blow out a candle.

 

[EndGame]

Tell me this, is the flu freestanding and open?

If there is a downdraft, it may well be because the flu is cold. There are many variables, but, this is one. Also, does the top of the flu extend at least two feet above the ridge of the home, or, is it at least eight feet from the ridge of the house?

Look at it this way, heat rises, but, if the flu is open, even though the smoke is warm, the flu may be cold by the time it reaches the top thus creating the backdraft. IF the flu is encased by masonry, you can fill the flu with formiculite masonry insulation to ensure the flu is warm and thus help the updraft, if it is a bare flu, open in other words, you can try wrapping it with insulation where possible to warm it. Also, it can help to light a small piece of paper prior to starting the main fire in the stove and allow the heat to rise up the flu, this can warm the flu enough to create the updraft needed to pull the smoke up and out of the flu as it should!

 

[bunker]

This describes your problem

May have to hire an engineer to see what can be done about the negative pressure in that part of the house.

EDIT - A good explanation of the effects of pressure in a home

 

[Moonbeam]

Find one of my posts and read it with your head in the fire pit. Then start the fire. The smoke will follow the rising hot air.

 

[Armitage]

What you probably need is a taller chimney. There is probably something nearby that is higher then the top of the chimney which creates the downdraft depending on the prevailing winds. Have you noticed any correlation based on wind speed & direction?

What kind of chimney is it (brick vs. double/triple wall metal)? How big & what shape is the inside of the flue (not the pipe off the stove, the main chimney).
Does the chimney go up the outside of the house or through the interior?

If it's a brick chimney with a large flue going up the outside of the house, it could be that the smoke cools off to much to rise all the way out. You can line these with double wall metal chimneys sometimes to improve the draft. ... smaller diameter & insulated better.

 

[Jeff7]

Well we've gotten some estimates for a good ventilation fan. But they said it'd be over $1000 for one! That was just nuts; I'll see what I can find at TrueValue's website in terms of chimney fans. I've been checking out this site now, and most of the suggestions they have, we've either tried already, or else they do the opposite of what's described. One thing on that site says that a warm chimney will help suck air up. When the fire is going good, the smoke just comes into the house even faster when the thing is opened; waiting until it's just a bed of coals seems to be the best time to open the stove.
We have had several people here looking at it, all with different suggestions - lengthening the chimney, cleaning, improving air flow into the house. So far, the improved air flow into the house has been the best, but the wind likes to shift often.
A little bit about observed conditions too:
The chimney is on the front side of the house, with the roof slanting down into the front yard. The smoke tends to blow down off the roof and right into the yard, and will readily flow back into the house through the front door or the new window.

If there is a downdraft, it may well be because the flu is cold. There are many variables, but, this is one. Also, does the top of the flu extend at least two feet above the ridge of the home, or, is it at least eight feet from the ridge of the house?

No to both it seems.

I'll have to check with my dad for chimney specs when he gets home; he told me to find out what I could online about this. He's not exactly Internet saavy yet. Begin training, he must.
Here's some pictures of the house and chimney:
The chimney. It has a cap on it, I'm guessing to keep rain out. We've not noticed any effect on the draft with it there, not like it's supposed to help of course, just...keep rain out. I have no idea what that thing laying behind the chinmey is. There are two pipes(flues?) in the chimney, one for the stove, and one for the fireplace upstairs, which we do not use.
Front of the house. Below the big window, a little to the left, at ground level, is the little window we had put in to allow more air into the house. When it's opened, slightly smokey air usually rushes into the house; that helps a little bit, but not always.

 

[EndGame]

Originally posted by: Jeff7
Well we've gotten some estimates for a good ventilation fan. But they said it'd be over $1000 for one! That was just nuts; I'll see what I can find at TrueValue's website in terms of chimney fans. I've been checking out this site now, and most of the suggestions they have, we've either tried already, or else they do the opposite of what's described. One thing on that site says that a warm chimney will help suck air up. When the fire is going good, the smoke just comes into the house even faster when the thing is opened; waiting until it's just a bed of coals seems to be the best time to open the stove.
We have had several people here looking at it, all with different suggestions - lengthening the chimney, cleaning, improving air flow into the house. So far, the improved air flow into the house has been the best, but the wind likes to shift often.
A little bit about observed conditions too:
The chimney is on the front side of the house, with the roof slanting down into the front yard. The smoke tends to blow down off the roof and right into the yard, and will readily flow back into the house through the front door or the new window.

If there is a downdraft, it may well be because the flu is cold. There are many variables, but, this is one. Also, does the top of the flu extend at least two feet above the ridge of the home, or, is it at least eight feet from the ridge of the house?

No to both it seems.

I'll have to check with my dad for chimney specs when he gets home; he recently told me to find out what I could online about this. He's not exactly Internet saavy.
Here's some pictures of the house and chimney:
The chimney. It has a cap on it, I'm guessing to keep rain out. We've not noticed any effect on the draft with it there, not like it's supposed to help of course, just...keep rain out. I have no idea what that thing laying behind the chinmey is. There are two pipes(flues?) in the chimney, one for the stove, and one for the fireplace upstairs, which we do not use.
Front of the house. Below the big window, a little to the left, at ground level, is the little window we had put in to allow more air into the house. When it's opened, slightly smokey air usually rushes into the house; that helps a little bit, but not always.

1) Have you tried it without the cap? And if so, you say there was no improvement?

2) The flu itself does not look to be in great condition. How long have you lived there and have you ever had a flu fire?

3) What size pipes are they? You say there are two pipes, but, the flu looks to be small. 8" round, or 9"X9" square are the smallest advised for wood stoves. 9"X13" is the most common size for most flus. Also, what is the flu lined with? Masonry clay liners, or, a reinforced S.S. pipe? I'm also assuming the flu is straight up from where the thimble enters it and has/is clean. A flu with many offsets or elbows can also present draft problems.

4) I have seen people use the fan method, but, don't recomend it, you are basicly negating the effects of the stove by drawing most of the heat up and out of the flu as well as increasing the amount of wood you will need to put through it.

I don't believe by the shots you gave that an extension to the flu would help a great deal unless there are unseen hills or something like a large building right beside you which is not evident. From the looks of it, the flu is about 2' - 3' from the ridge and reaches above the ridge height by at least 18" - 24".

IF the flu is lined with clay liners, it IS possible the problem is a result of busted liners which would have most likely been the result of a flu fire. This can also happen with SS pipe liners, but, is much more less common. If you haven't done so, clean the flu or have a professional chimney sweep check the flu for broken liners or blockage.

You do apparently have a bad problem and pressure may well be playing a part, but, since you added the window, I'm doubting that.

 

[Armitage]

height of that chimney looks marginal. Code here requires the top of the chimney to be 2 feet higher then anything within 10'. Since it's not on the outside of the house, it's probably not the cold flue issue.

You say the wind blows the smoke down over the front of the house? Maybe those trees behind the house are creating the downdraft when the wind blows from behind the house. Again, chimney haeight could probably help here.

 

[Armitage]

Have you noticed a correlation between wind direction and the draft problem? Do you have the problem when the wind blows toward the front of the house?

 

[Armitage]

This article may be of interest: Chimney Sizing

What does the pipe look like coming off the stove? How far does it rise before it turns 90deg to enter the chimney?

May be a stupid question, but I've got to ask...
Are you sure you know which way your damper operates?

 

[Sundog]

Good luck to you. I just inserted a SS liner in our flu today and hooked it up to a new wood burning insert.

 

[Jeff7]

Originally posted by: EndGame


1) Have you tried it without the cap? And if so, you say there was no improvement?

2) The flu itself does not look to be in great condition. How long have you lived there and have you ever had a flu fire?

3) What size pipes are they? You say there are two pipes, but, the flu looks to be small. 8" round, or 9"X9" square are the smallest advised for wood stoves. 9"X13" is the most common size for most flus. Also, what is the flu lined with? Masonry clay liners, or, a reinforced S.S. pipe?

4) I have seen people use the fan method, but, don't recomend it, you are basicly negating the effects of the stove by drawing most of the heat up and out of the flu as well as increasing the amount of wood you will need to put through it.

I don't believe by the shots you gave that an extension to the flu would help unless there are unseen hills or something like a large building right beside you.

IF the flu is lined with clay liners, it IS possible the problem is a result of busted liners which would have most likely been the result of a flu fire. This can also happen with SS pipe liners, but, is much more less common.

You do apparently have a bad problem and pressure may well be playing a large part, but, since you added the window, I'm doubting that.

1) Without the cap, yes. No discernable effect on performance.
2) We've been here about...16 years I think? I don't think we've ever had a flue fire.
3) Do not know, I'll post detailed info when I can ask my dad.
4) Yeah, it seems that drawing heat out of the house is almost unavoidable with a stove, to some degree anyway.
To the sides of the house are just more trees, then other houses.

I was also informed that we never did actually try an extension on the chimney; don't know why, cause it sounds like it would be fairly cheap to try.

May be a stupid question, but I've got to ask...
Are you sure you know which way your damper operates?

Yup; just went and double checked for the heck of it. Turn the knob horizontal, much smoke comes in. Turn it upright, much less smoke. Right now, the draft seems half-decent - only a little smoke comes in when the front is opened, and air rushes in the window when it's opened all the way.

Oh yes, here is a picture of the stove setup downstairs.

 

[Armitage]

Originally posted by: Jeff7

Originally posted by: EndGameOh yes, here is a picture of the stove setup downstairs.

Looks OK, just wanted to make sure you had a decent vertical rise straight off the back of the stove ... ie. not a horizontal run before going vertical.

 

[EndGame]

Originally posted by: Jeff7

Originally posted by: EndGame


1) Have you tried it without the cap? And if so, you say there was no improvement?

2) The flu itself does not look to be in great condition. How long have you lived there and have you ever had a flu fire?

3) What size pipes are they? You say there are two pipes, but, the flu looks to be small. 8" round, or 9"X9" square are the smallest advised for wood stoves. 9"X13" is the most common size for most flus. Also, what is the flu lined with? Masonry clay liners, or, a reinforced S.S. pipe?

4) I have seen people use the fan method, but, don't recomend it, you are basicly negating the effects of the stove by drawing most of the heat up and out of the flu as well as increasing the amount of wood you will need to put through it.

I don't believe by the shots you gave that an extension to the flu would help unless there are unseen hills or something like a large building right beside you.

IF the flu is lined with clay liners, it IS possible the problem is a result of busted liners which would have most likely been the result of a flu fire. This can also happen with SS pipe liners, but, is much more less common.

You do apparently have a bad problem and pressure may well be playing a large part, but, since you added the window, I'm doubting that.

1) Without the cap, yes. No discernable effect on performance.
2) We've been here about...16 years I think? I don't think we've ever had a flue fire.
3) Do not know, I'll post detailed info when I can ask my dad.
4) Yeah, it seems that drawing heat out of the house is almost unavoidable with a stove, to some degree anyway.
To the sides of the house are just more trees, then other houses.

I was also informed that we never did actually try an extension on the chimney; don't know why, cause it sounds like it would be fairly cheap to try.

May be a stupid question, but I've got to ask...
Are you sure you know which way your damper operates?

Yup; just went and double checked for the heck of it. Turn the knob horizontal, much smoke comes in. Turn it upright, much less smoke. Right now, the draft seems half-decent - only a little smoke comes in when the front is opened, and air rushes in the window when it's opened all the way.

Oh yes, here is a picture of the stove setup downstairs.

OK, from the last picture, I'll bet it is lined with clay liners. This could be a problem IF there are broken liners. This should be easy to check yourself by getting on the roof with a flashlite and looking down the flu (with the fire out of course)

The stove itself looks to be one of the airtight models which many have a tendancy to smoke back more than conventional stoves, but, should not be as bad as you describe. The setup into the flu through the thimble looks fine IMHO and should work.

I'd check out the liners, if they are intact, you're right, the next logical step would be to add a section on top of the existing liner and see if this works, especially since it's hard to tell the exact circumstances surrounding your home and the flu. This you should have no problem doing yourself, but, if there's any question, call a local chimney swwep or contractor for advise or assistance.

 

[Ly2n]

Originally posted by: Jeff7
The chimney is on the front side of the house, with the roof slanting down into the front yard. The smoke tends to blow down off the roof and right into the yard, and will readily flow back into the house through the front door or the new window.

Looking at your pictures and reading what you posted above, I think that something around your house is causing the downdraft. The smoke coming down the roof and ending up in the front yard implies that the nornal direction for the air movement is downward. It looks like you have a normal double flue chimney probably with 12x12 liners. Counting the exposed bricks to the top, it looks like extending the flue might be a good idea. However extending the flue requires removing the weather cap on the chimney and adding more layers of brick and recapping. Its not to hard and it can be done, If you are going to do it I suggest that you go up the full 2 feet length of the flue, don't try to only go half way.

 

[EndGame]

Originally posted by: Ly2n

Originally posted by: Jeff7
The chimney is on the front side of the house, with the roof slanting down into the front yard. The smoke tends to blow down off the roof and right into the yard, and will readily flow back into the house through the front door or the new window.

Looking at your pictures and reading what you posted above, I think that something around your house is causing the downdraft. The smoke coming down the roof and ending up in the front yard implies that the nornal direction for the air movement is downward. It looks like you have a normal double flue chimney probably with 12x12 liners. Counting the exposed bricks to the top, it looks like extending the flue might be a good idea. However extending the flue requires removing the weather cap on the chimney and adding more layers of brick and recapping. Its not to hard and it can be done, If you are going to do it I suggest that you go up the full 2 feet length of the flue, don't try to only go half way.

Not arguing here, simply pointing out things which are obvious after studying the photos. I would agree as stated, except that the liner is not a 12"X12"! At most it is a 9"X13", but probably a 9"X9". Why? Well, counting the length of the flu, it is 3 brick wide or 24 2/3". The liner is not 1/2 the width. Add to that the fact that there is a 9"X9" liner sitting on the roof behind the flu and I'm almost positve! LOL!

Now, as far as heighth, there are 14 exposed courses of brick from the roof level inside the flashing to the top course, then a 3 inch coping, plus the amount the liner is extended above the coping which makes it about 56" total. The flu is approx. 3' from the ridge of the roof which makes it about a 2' decline. Taking everything into consideration, there should be sufficient (according to codes) clearance above the ridge. Now, as stated though, conditions can vary as stated. As for the smoke going into the yard, it looks as if a hill rises behind the house. This could account for the outside downdraft but should not be that detrimental to the flu as far as functioning correctly. I personally am still thinking that you have damaged or blocked liners in the flu causing this and would look at this first and foremost. If none can be detected, and the flu is clean, then look into raising the flu one section.

Good Luck!

 

[Jeff7]

Added an update to the top. I do know now that the flue does not appear cracked, and that we have clay liners.

 

[db]

I can't really tell from the picture what the chimney cap looks like.
Anyway FWIW I remember reading in an old trade book that the best configuration is a simple flat sheet of metal above the opening of the chimney top. That is supposed to be the best compromise for draw and weather treatment. I cant remember the ideal distance from outlet to flat sheet, but it's maybe 4-6 inches--in other words, not real close or real far.

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[Jeff7]

Originally posted by: db
I can't really tell from the picture what the chimney cap looks like.
Anyway FWIW I remember reading in an old trade book that the best configuration is a simple flat sheet of metal above the opening of the chimney top. That is supposed to be the best compromise for draw and weather treatment. I cant remember the ideal distance from outlet to flat sheet, but it's maybe 4-6 inches--in other words, not real close or real far.

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That sounds like what it is over it right now; it's a pretty basic cap.

 

[Sundog]

Be sure to post exactly what the chimney sweep says. Sounds like there are several of us that are very interested!

 

[tomjoey]

in 25yrs. never had downdraft problem til past few days. This "Post" is providing some useful insight so far. Stovepipe is clean... flue free of any obstruction, although some creosote build-up couple of feet above thimble... reasonably clear remaining 18'. How much of a role does weird, abnormal atmospheric pressure play w/downdrafts ??

 

[amith1]

we purchased a house last year, with a wood stove. we have the exact same problem. there are 2 chimneys next to each other, the one works perfectly for the fireplace upstairs, the one for the woodstove downstairs- our house is pretty much always filled with smoke when we try and use it. I had a downdraft problem in another house, and I used a blow dryer until the heat went up- worked fine. Nothing helps this stove- and you open the door to put wood in and the smoke pours out. we are now considering getting rid of this entire set up and putting a pellet stove in another area. so sick of this! I am very interested in the resolution to this.