Negative Pressure and Beyond!?

Ok. I know we have negative pressure—without a doubt. Our house is a split level, with 2 fireplaces right on top of one another (each having their own flue). When having our first fire in the upstairs fireplace we noticed smoke coming in the downstairs fireplace. Our immediate solution was to replace the downstairs damper with an air tight damper at the top of the chimney, but that didn't work. Next, I decided that we wont use the downstairs fireplace this season, so I silicone sealed the iron damper door at the bottom of the chimney. Well that did work, but the smoke found other entry points into the house and the smoke ended coming into the downstairs room though one of the recess light cans. What the...???

Can someone please give us some idea as to what's going on, and what a solution MAY be, so we can speak to a specialist about this somewhat intelligently.

Thanks so much.

 

36lpi,

What is going on is that you are pushing more air out of your home that is being allowed to come in.
This is common with homes that are air tight.
If you have an exhaust fan(s) running or a gas water heater or furnace you will make the matter worse.
This is potentially a dangerous situation and would suggest you not use the fireplace untill someone has fixed the problem and declared it safe.

Do you perhaps have a combustion air damper in your fireplace(s) you have not opened?

 

If I understand correctly, you still get smoke crossing over into the other fireplace even with the top sealing damper closed?

It's possible that maybe the seal on the top sealing damper is not functioning properly.

However, I would suggest contacting a chimney professional who offers an internal video inspection of your flues. You may have some breeches in the upstairs lining, possibly in the downstairs lining, too.

In my experience, if it is a "crossover" problem you may see (with the camera) cracked flues, open/deteriorated mortar joints, or possibly dry stacked flues (flues that were stacked with no mortar between).

As a heads up, if you do find breeching in the lining, two common and accepted methods of repair are to replace the lining with a stainless steel liner or to replace it using a cast-in-place/poured lining system.

Googd Luck! Let us know what you find out

 

Thanks everyone... Do any of you have any idea as to how much it could cost to solve this problem? A range?

Greg - What exactly is a combustion air damper? Is it a hole into the chimney that allows air in to feed the fire, rather than the fire stealing air from within the home?... We do have a small iron door at the base of the chimney on the exterior. Is this it?

 

36lpi,

That door at the base of the chimney will be the chimney clean-out.
It is where you would shovel out the crud that chimney cleaning releases.

There is often an opening either at the back of the firebox or sometimes incorporated into the floor or wall next to the fireplace opening.
This will be connected to the outside as an air source for the fire.

It sounds like if the smoke is finding its way in cracks on the outside you really have a problem.
What else do you have running that would cause such a negative draw?

Another possibility is a breach in the chimney that is causing smoke not to crossover but enter the house through the chimney chase.

Better get this checked before you burn any more wood.

 

Thanks, Greg... I'm looking into it.