Solutions for smoke leaking out the wood-burning appliance

[JohnBaker]

I’m used to being able to research and solve technical problems, but so much of solving draft problems seems to be trial and error, so I’d appreciate input from those more experienced.

Our 28 year old house has a square clay flue liner with 6” internal dimensions. The length from thimble to chimney termination is 23’. I clean it myself every year. It’s a relatively straight shot from the top to the ash pit below the thimble. I had an endoscope down the entire length earlier this summer. There are several cracks in the upper two sections in the chimney above the roof. Other than that it looks fine.

Most of our wood stove use is in high humidity conditions slightly above the freezing point (we’re near the coast). It is our auxiliary heat source for the not infrequent winter power outages. The location has an underfloor 4” diameter PVC pipe for combustion air intake. The pipe is about 10’ long and is completely clean from one end to the other.

The wood stove that we replaced this year never had great draft. Because it’s in a relatively small room, using it would drive us out of the room fairly quickly. We replaced it with a masonry heater this summer. That has solved the problem of being able to be in the room at the same time that a fire is burning. Because it extracts more heat from the flue gases, though, the draft problem has become worse.

I’ve experimented with everything available to improve the situation “upstream” of the chimney (allowing room combustion air in, opening windows, pressurizing the house with the HRV, smaller fires at the beginning, smaller wood diameter, pre-heating the unit with electric heat, etc.). The only thing that solved the problem, completely, was the temporary installation of a tiny (0.3 amp) fan atop the chimney. So I know that installing a permanent chimney fan will solve the problem, but there are some issues with that, the main one being what happens when the power goes out just after I’ve lit a fire? I’ve been thinking about battery backup.

But, would relining the chimney with a stainless steel liner solve the draft problem and remove the need for the fan? My guess is “no”, but I can’t determine a way to figure out the answer, hence the request for input. The masonry heater manufacturer says to use a 6-8” flue. I’m fairly sure that a 6” single-wall liner isn’t going to fit inside a slightly irregular 6” ID square clay flue liner, so would require breaking that out. To use double-wall and to insulate it (both for better draft) would certainly require it. Hmmm…all that extra work and expense and it might not solve the problem.

Any thoughts, please?

 

[begreen]

Is the masonry stove being fired with a good hot fire? How dry is the wood that is being burned?
Pictures please of the stove, the stove connection to the chimney and a good shot of the chimney outside.

 

[jetsam]

23' is a decent run. There's no question that an insulated liner of appropriate size will draft much better than a too-large clay and masonry stack, most especially if it is an exterior chimney.

You need to figure out what the appropriate flue size is for your heater- someone here can likely help. If 6" round is about right, you will probably need to break out the clay liner to fit an insulated liner in. The manufacturer's spec is really vague... 6" round is 28 square inches of flue cross-section. 8" square is 64 square inches. That's a pretty good variance, and I have to imagine that a small masonry heater will do better on the lower end of that range.

How tall is the chimney relative to the roof peak, and what is the distance between the roof peak and the top of the chimney?

You can also try adding an extension to the top of the flue, but I think you're going to be better served by figuring out the correct flue size and insulating it.

 

[begreen]

I'm wondering if this is a poorly located chimney in a windy area, thus the request for some pictures.

Is this on the straits of Juan de Fuca?

 

[JohnBaker]

Thanks for the responses. We’ve only had a dozen fires so far. In answer to the questions:

• I’ve been firing it as hot as I can, using wood sections no larger than 3” diameter and most quite a bit less.
• I don’t have a wood moisture meter, but all the wood that I’ve been burning so far has been under cover and split for 2-3 years. It is very dry.
• There has been little to no wind on the days that we’ve been using the heater so far.
• From the house drawings, I can see that the top of the flue is about 2 feet higher and 10 feet laterally from the peak of the roof.

I can’t get other photos today, but I’ve attached a photo from when I completed the single-wall stove pipe from heater to thimble earlier this fall. It’s about 36” of pipe. It wasn’t possible to use double-wall because the thimble exits the chimney at an angle. The chimney is interior to the house, with 13 feet in conditioned space, 5 feet in the uninsulated attic and the top of the flue 5 feet above the roof. The ambient air temp during our testing has been 40-50F.