Fireplace smoke comes in through pellet stove

[druderman]

On the main floor of my house I have a fireplace.
In the basement directly below I have a pellet stove.
They each have their own flue in the same chimney.

If I light a wood fire in the fireplace while the pellet stove is off, I will get a smoke condition in the basement.
There will be mostly the smell of smoke, but it won't be visible.
It won't be that bad, but this sure explains why the room smelled smoky when I first moved in.

When I fire up the pellet stove while there is a fire in the fireplace on the floor above, the smoke condition goes away.

I have made sure that the cap on the top of the chimney for the pellet stove flue was secure and sealed (it originally wasn't).
My house is fairly quite porous to air, so I find it hard to believe that the fireplace draws so much air that it is pulling air through the pellet stove from the basement.
I'm pretty sure that I've tried opening a nearby window to see if that will stop things, but didn't notice a difference.

Does anyone there have an idea what is going on and what I might do about this?

Thanks,

-dave

 

[jtp10181]

Could be a few things. The fireplace on the main floor, I assume is a traditional open masonry fireplace? Those suck massive air out of the house while in use. The basement is the lowest pressure zone in the house, as the fireplace sucks are out its depressurizing the lower level. You could try opening a basement window while burning the fireplace to see if it helps.

Does the pellet unit have a stainless liner running up through a masonry flue, or does it just dump into the flue? Have you ever had both flues inspected to make sure there is no cracks between the two?

How are the caps on the roof, same height? How far apart are they?

 

[druderman]

I will try opening a basement window next time I light the fireplace, but of course I don't want to chill my basement any more than it already is.

Yup, I have a masonry fireplace, and yes, the pellet stove has a stainless steel liner.

No, I have not had the adjoining flues inspected for cracks.

Both chimney caps are at the same height and are perhaps 2 feet apart.

 

[jtp10181]

Extending the flue for the fireplace would probably help a lot. Another 2ft up would do it some good.

I think for two wood flues for them to be the same height they would have to be 3 ft apart to meet code. Might be the same for pellet / wood but I would have to look it up.

 

[crausch]

I would have to agree with jtp10181. My first assumption would be that the smoke coming out of the fireplace flue at the top is simply being drawn right back down through the pellet stove pipe from the negative pressure in the basement.

 

[dac122]

I would have to agree with jtp10181. My first assumption would be that the smoke coming out of the fireplace flue at the top is simply being drawn right back down through the pellet stove pipe from the negative pressure in the basement.

That was my gut reaction as well. Can you have someone come over with a sensitive CO monitor and have them probe around the pellet while you have a fire burning?

 

[druderman]

I would have to agree with jtp10181. My first assumption would be that the smoke coming out of the fireplace flue at the top is simply being drawn right back down through the pellet stove pipe from the negative pressure in the basement.

That was my gut reaction as well. Can you have someone come over with a sensitive CO monitor and have them probe around the pellet while you have a fire burning?

I have a new regular over-the-counter CO detector which doesn't go off in my house.
But I guess it's obvious that there is smoke coming in, since it smells like smoke.

So I should add a couple of feet to the flue, eh?
Right now it has a keep-the-rain-and squirrels-out cap.
Would I need to call a mason/chimney guy, or can I just buy something at the HW store to do the trick?

 

[jtp10181]

You can get one clay tile same size as you have now and just dump it up there with some mortar and then put the cap back on top of that. I have heard those things are so damned heavy there's no way it could fall off.... if it seems unstable you might need to use some flat metal braces with tapcon screws to hold it tight.

 

[druderman]

So you mean strap another clay pipe length on top of the existing one. And wrap it w/some metal. Hmmm. Doesn't sound hard, except for that part about perching on top of the chimney. Did I mention that the roof is very steep? Gulp!

 

[ChandlerR]

You know, maybe the chimney cap is letting the smoke go out sideways rather than up so it flows over the top of the pellet stove flue. A little negative in that flue and down it goes. Once the pellet stove is working you have a draft and the smoke goes up.
I think that an extension would work but so may simply removing the cap...even temporarily to see if it works.

Chandler

 

[druderman]

Man, you guys are helpful.

For the record, my brick chimney is a little less than 6 feet wide and has 3 parallel flues. A fireplace flue. An old basement fireplace flue with pellet stove insert and stainless steel flue. And mystery flue which gets exhaust from my gas hot water heater (maybe once the furnace). Our gas furnace is fairly new and vents out the side of the house through PVC. The house is about 35 years old.

 

[jtp10181]

If your water heater is b-vent the smoke could be coming down that also, FYI

 

[dac122]

In some places code restricts using a common chimney flue. Find the source and then solve the problem.

 

[jtp10181]

In some places code restricts using a common chimney flue. Find the source and then solve the problem.

He has 3 flues and 3 appliances.... so.... point is?