Expert: James Ball - 10/31/2008

Question
Hi James,

I have a 30-yr old 2-story home with forced air (heat pump w/ oil furnace backup) and a fireplace in eastern PA.  The fireplace flue and furnace flue are side-by-side in the same brick chimney.  The fireplace flue has an additional length of terracotta liner on top (an attempt to get above the furnace flue top and also a bit higher above the roof peak) and stainless caps to keep the animals, etc. out.  There is no deliberate "furnace combustion air" supply into the basement, nor a deliberate "fireplace combustion air" intake into the fireplace.

When we use the fireplace, I can usually smell the smoke in the basement, coming from the damper on the furnace flue pipe.  If the draft in the fireplace pulls enough cold air into the house, it can kick on the heat because it goes right past the thermostat on its way into the den and up the fireplace.  When that happens, if it's warm enough outside to still use the heat pump, I can SEE the smoke in the basement and lots of it.  I think the metal return ducting in the basement is leaky enough, and the furnace flue is the path of least resistance, so it draws the smoke down the furnace flue when the circulator fans kicks on (as long as the furnace is not firing, anyway).

Obviously, I can't use the fireplace like this.  I've tried troubleshooting various things, and have made some improvements (like reducing the return leaks I can access at the duct joints and joist panning), but I don't have a good idea of where I'm going to get the most bang for my buck next.

Is there a way for me to check if there are big leaks between the two flues, or is this not a big deal either way?

Is there a way to add a fresh air intake to the fireplace so that the draft does not tend to draw air from the house?

Are the flue caps adding to the problem enough that it's worth removing one or both?

Unfortunately, the professional advice I've gotten so far has not involved a well-thought-out solution but does involve me spending lots of money on that particular person's field of expertise.  The chimney guy wanted to sell me a $2500 stainless liner for the furnace flue, the HVAC guy wanted to replace the return ducting for $5000, but neither wanted to do any TESTING to demonstrate a problem that their product will fix.

Any advice or direction is much appreciated!

Thanks in advance,

Dave

Answer
Hello Dave, I would have a local Certified Chimney Sweep (www.csia.org, there you can look up by zip code to find one near you) take a first hand look at what you have. They might want to video scan the 2 flues to be sure no breaks, maybe leave a window open in the boiler room? Maybe make the taller flue even taller?
That might stop the smoke but it will still pull air into he home...you need make up air for the house, 10 gallon of air per minute going up the chimney then the house needs 10 gallons of air to replace it and it will come from the path of least resistance for example.
keep me posted
James