Wased energy through your stove pipe.

[Wallybear]

I am sure that most people have seen the reclamation fans on wood stove pipes. These are sealed boxes that have pipes running through the stove pipe and a fan to push out heat that would have been wasted going up and through the stove pipe.

These do capture heat but it is a very small percentage. Why not build a large mass around the pipe to capture more of that heat and release it slowly back into the house? I am thinking much like the rocket stove rely on these massive heat retainers you could do the same with a wood stove pipe. Why not build a clay surround on the pipe that is say 18" thick? You will have to build a structure to hold it up and in place, but they energy transferred into the mass is all saved energy not wasted out the pipe.

 

[Marianne]

Ya, no kidding. Gobs of heat going up that pipe and I think about it often. Our floors sure won't support the added weight of the thermal mass and it's virtually impossible to get underneath that area to add support. We also remove the stove pipe every year for brushing clean and inspection while standing on the ground.

The blower went out on our woodburner after one year. I bought a little Stanley workshop fan to blow air through the air space on the back of the stove where the blower air was. It doesn't fit all the way back, so half the fan blows straight up. That catches the warmer ceiling air and circulates around the stove pipe. Catches some of the lost heat, but tons more is just lost up the pipe.

I just did a quick search and found this from Erica Wisner:

Cob weighs about 95 lbs/square foot, maybe 80 lbs/sf when you subtract the ducting voids. Brick and concrete (used in foundations and burn tunnel) are 100-150 lbs/sf. An 18" tall cob bench might weigh 2-5 tons, but it's spread out at about 140 lbs/sf.

http://www.permies.com/permaculture...e-energy/rocket-mass-heaters-on-wooden-floors

I wish we could do some thermal mass like you suggested. Going straight up with the cob will put a lot of weight in one area, plus you already have the weight of the stove there, too. We have newer, good floors with 2x10 treated joists, 3/4 plywood and 3/4 T&G subfloor over that...but I'd still be too afraid to put that much mass vertically without a solid concrete foundation under it.

Next house will be different.............

 

[Bubblingbrooks]

Stack robbers are a good choice, if weight issues are at stake.
They are not the most attractive thing, but cost is relatively low, and its easy to install.

 

[Marianne]

I had to google stack robber, as I wasn't sure if it was the same thing as the heat exchanger (it is). Found this:
http://www.chimneysweeponline.com/horobber.htm

Since we have a 'high efficiency' (ya, right) airtight stove, guess we aren't supposed to use one. BB, is yours noisy? I have read conflicting posts on that.

We have a dinky cast iron stove in our shop. It's been years since we have fired it up, but I liked it better than the newer EPA blah-de-blah one we have in the house.

 

[Bubblingbrooks]

I had to google stack robber, as I wasn't sure if it was the same thing as the heat exchanger (it is). Found this:
http://www.chimneysweeponline.com/horobber.htm

Since we have a 'high efficiency' (ya, right) airtight stove, guess we aren't supposed to use one. BB, is yours noisy? I have read conflicting posts on that.

We have a dinky cast iron stove in our shop. It's been years since we have fired it up, but I liked it better than the newer EPA blah-de-blah one we have in the house.

We do not have one yet, but they are common up here, and its on the list. It will get done. That, or we will put in a masonry heater.

 

[Bubblingbrooks]

The other things that are viable options, are a downdraft stove, or, running pipe out through the ceiling of the room and back again.
I think stack robber might have been what the OP was referring to, and the extra pipe was my thought process...

Downdraft stoves are mandatory in many northern countries.