It works... heat exchanger added to existing heater...

Hey all,
First post here as I just ran across the permies forums. This last January we re located our business from San Diego to Licking Missouri. As a result in a few days time we went from 70* weather to 6* weather. Not having experienced this low of temp reading in So Cal it did get my attention. The existing shop wood burning heater became my obsession very quickly. Problem being that no matter how much wood I fed it not enough heat would get transfered into the 4000 sq. ft. Building to do any good. It was impressive looking, and processed a large amount of wood very quickly, but produced very little radiant heat. I was determined not to spend another winter in that work environment.

Not knowing a thing about wood burning stoves I searched the internet and learned a lot,  but not too much on the size and scale that I was thinking about. So I guessed and hoped that logic would prevail. The old existing stove / heater...

So I chopped it up and built a heat exchanger for the top of it. Lit it off for the first time a few nights ago and raised the shop temps from 38* to 62* in just over an hour. Im so happy this thing works and that the effort was worth it. Now that I know it works im anxious to do some sheet metal shroud work to make it more efficient. Im always looking for improvements so dont be quiet! Any advice from you wood stove Gurus? Appreciated in advance!

Nice work!  And welcome to Permies!  What were the mickey mouse ears for on the original?

Does you heat exchanger have a fan pushing air through it?

Mike Haasl wrote:Nice work!  And welcome to Permies!  What were the mickey mouse ears for on the original?

Does you heat exchanger have a fan pushing air through it?

Im not sure what the thinking was there? They were tapped into the main stove body through a 6” tube towards the back. I capped them off. Then the exhaust was T’ed off of them at the front and ran down the center if of the stove parallel to the ground where it attached to the chimney. Think they were thinking more surface area to radiate heat from?  

I have a squirrel cage in the back that works very well and moves a lot of air. Im thinking about building a shroud around the heater and ducting that to the fan inlet to pre heat the air before being blown into the exchanger.

Ahh, I see now.  They were probably just giving extra surface area.

I'm not sure if sending warmer air into the fan would give you more heat overall into the shop or not.  I guess it would let less air rise up and heat the ceiling and put more downwind of the fan.

Another thought would be to put something in each pipe so that the air flows turbulently down the pipe.  That should give a bit better heat transfer.  1%, 10%, I don't know...

The temp in the oven was close to 300* and with the fan on for about 5 minutes I could touch the inlet tubes in the back and they were cool to the touch.. couldnt get close to the outlet end of the tube... only 5’ long. Amazing how much heat is transfered.
Seems like any type of restriction of flow would help. The fan is on a dimmer pot, low speed the heat is greater longer, high speed= cooler and quicker dissipation of heat? And at what point is it good enough? But it is fun goofing around with it... 👍

I didnt want to use a 50 gallon drum as I was hoping to find something heavier and thicker. Found this lawn roller at a local flea market and it worked out just fine. 16ga. Around 18ga on the ends.

Because of the poor design of the existing stove I couldn't reload the wood without filling the shop with smoke! There was no way to avoid this problem!  I did add a few dampers and sealed up the doors as well as redirected the exhaust straight out of the burning chamber. Just that helped a great deal! But I still had open door smoke issues. After some thought,  I cut in a fresh air injector tube into the chimney just past the T in. Found a $20.00 blower unit at the same flea market and gave it a try. I was pleased with the results so i did the permeant mount to it. Now to remember to open the damper and turn on the fan prior to reloading! LOL

Looks like you've got some good improvements going on. I'd be interested to hear how your chimney looks at the end of the season.

Grady Houger wrote:Looks like you've got some good improvements going on. I'd be interested to hear how your chimney looks at the end of the season.

In terms of?
Im almost willing to bet its never been cleaned. 30' or so tall its not an easy task to clean it.
I was really surprised at how much soot was in the mouse ears when I lopped those off. They were 1/4 full of soot. The horizontal section of the exhaust tube that runs to the chimney was half way full with soot. There is a clean out on the bottom of the chimney. Once I cleaned it out It really starting drawing air!

One would think that an ex government building would of been maintained a bit better?

What grade of pipe did you use in the heat exchanger? I'm looking at doing something similar in my shop.