I seem to be having a problem with downdraft/negative pressure in my fireplace. I had the chimney cleaned on Saturday and sat down for a nice fire that night. First I had a little trouble getting it going, but then realized that smoke was backing up in my basement. It was actually coming out of furnace exhaust pipe in the crawl space. I opened a window downstairs and cracked a window in the living room (where the fireplace is) and it helped a little. When the furnace is on and the fan is blowing, the smoke does not back up in the basement. The chimney sweep said they cleaned both pipes and that he tested the draw on the furnace pipe and it was working. The smoke doesn’t come back out of the fireplace, which means that it must be pulling up the chimney and then back down into the basement. The house was built in 1950, so you know it isn’t tight. Any ideas on how to correct the problem. Do you think the HVAC guys can help? I had a new furnace installed about 2 years ago and I wonder if it was installed incorrectly. I have caps on the chimney and it appears to be the proper height. My neighbor has a huge weeping pine tree that could be contributing to the downdraft, but to see smoke coming out of a pipe downstairs seems very odd. We always had a little smell for about a day or so after having a fire, but never smoke in the house. Any ideas? Thanks for your help.
Downdraft/negative pressure
- Thread starter kmanfire
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Open fireplaces vent a huge amount of indoor air up the flue. Having a smoke smell after a fireplace burn (or stove burn for that matter) isn't normal, so it sounds like the problem has been around for a while and maybe certain conditions that night made it bad enough for you to actually see the smoke. This is a somewhat dangerous situation as both the fireplace and furnace exhaust can contain carbon monoxide - so if you don't have a good, working detector, I'd recommend getting one immediately. Beyond that, some things you can try:
1. The wood appliance flue should be taller than the gas appliance flue...I forget the exact number (18 inches?), but there are extenders available. Not really a fix, but if the FP does pull negative pressure, hopefully the furnace flue will be pulling in clean air.
2. Close any fireplace doors (or install them if your FP is rated for them) to help reduce the FP appetite for room air.
3. Crack a window in the fireplace room to help supply additional air without having to pull it back through the furnace pipe.
4. Make sure no other appliances are contributing to the problem...clothes dryers, bath exhaust fans, kitchen cook hoods, etc can all vent indoor air out and make any draft problems worse.
5. If there are any good chimney sweeps in the area, it might not hurt to have one come take a look and evaluate the set-up. There are thousands of things a set of eyes actually looking at the problem can see versus trying to make an internet diagnosis with one paragraph description.
6. Consider installing an actual fireplace insert or wood stove. It won't pull as much air out of the house as the fireplace and you will actually be heating the house with your wood burning and may even be able to shut the furnace off.
1. The wood appliance flue should be taller than the gas appliance flue...I forget the exact number (18 inches?), but there are extenders available. Not really a fix, but if the FP does pull negative pressure, hopefully the furnace flue will be pulling in clean air.
2. Close any fireplace doors (or install them if your FP is rated for them) to help reduce the FP appetite for room air.
3. Crack a window in the fireplace room to help supply additional air without having to pull it back through the furnace pipe.
4. Make sure no other appliances are contributing to the problem...clothes dryers, bath exhaust fans, kitchen cook hoods, etc can all vent indoor air out and make any draft problems worse.
5. If there are any good chimney sweeps in the area, it might not hurt to have one come take a look and evaluate the set-up. There are thousands of things a set of eyes actually looking at the problem can see versus trying to make an internet diagnosis with one paragraph description.
6. Consider installing an actual fireplace insert or wood stove. It won't pull as much air out of the house as the fireplace and you will actually be heating the house with your wood burning and may even be able to shut the furnace off.
deadon
New Member
Do the furnace and fireplace have separate flues? Are they close to each other? If they are sometimes when the furnace comes on it will pull combustion air from the fireplace. This will cause smoke to enter the house. If you have a negative indoor pressure it is most likely insufficient combustion air.
oconnor
Minister of Fire
What you are descibing is stack effect - it can effect lots of homes, old, new, tight or not. I had it as an issue on our 1960's bungalow, and it got worse when I ran the basement stove.
The best way to tackle stack effect is to air seal, especially attic hatches and leaky basement windows, and old fireplaces. That basement crawlspace pipe basically became a cold air return into your house, and it isn't going to change unless you change it.
The stack extension described above will reduce the amount of smoke that enters the house, but not the amount of air that enters. Every cubic foot of air that is exhausted out the flue of the upstairs fireplace must be replaced, and it will come from wherever is easiest. If you get the house completely sealed, then using the fireplace will become impossible, 'cause there won't be any air to exhaust, 'cause non is coming in.
Getting an insert will help (and it will actually give you heat, as opposed to just light and smoke), but the truth remains - all air that exits must be replaced. If you want some more reading on what is happening to your house, read thru the "Residential Guide to Wood Heating" in my signature block. Lots of good info there about what is happening and what can help the situation.
The best way to tackle stack effect is to air seal, especially attic hatches and leaky basement windows, and old fireplaces. That basement crawlspace pipe basically became a cold air return into your house, and it isn't going to change unless you change it.
The stack extension described above will reduce the amount of smoke that enters the house, but not the amount of air that enters. Every cubic foot of air that is exhausted out the flue of the upstairs fireplace must be replaced, and it will come from wherever is easiest. If you get the house completely sealed, then using the fireplace will become impossible, 'cause there won't be any air to exhaust, 'cause non is coming in.
Getting an insert will help (and it will actually give you heat, as opposed to just light and smoke), but the truth remains - all air that exits must be replaced. If you want some more reading on what is happening to your house, read thru the "Residential Guide to Wood Heating" in my signature block. Lots of good info there about what is happening and what can help the situation.
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