Heat Exchange Improvements

Heat Exchange Improvements

PostBy: madrmc On: Mon Feb 27, 2006 8:10 pm

Just wanted to get opinions about whether your stove could exchange heat better. I have an Alaska Channing stoker and the heat exchange is no more than the top of the stove vs. the air that a squirrel cage blower moves over it. There is about a 2” air gap between the top of the stove and the “hood”.

I’m no engineer, but I think heat exchange would greatly improve by adding finned aluminum pipe and letting the air blow in between the fins (not the pipe itself). I was trying to find an illustration online. This site isn’t too bad with an imagination:
**Broken Link(s) Removed**. This way you would increase the surface area, and use a material that is a much better conductor (alumumin vs. steel). The temperatures of the air coming out would have to be a lot hotter.

Also there’s no type of heat exchanger on the side of the stove, and the sides are very hot to the touch even on lower settings. You might be able to build in some heat exchanger on the sides.

I know that Keystoker has an internal heat exchanger and claims 88-90% efficiency. Alaska has said that their stokers average 76% and their isn’t a formal heat exchanger. It seems like this would be time well spent, something that could add to BTU output no matter how fast you’re running it.

Stove/Furnace Make: Alaska
Stove/Furnace Model: Channing III

Re: Heat Exchange Improvements

PostBy: davemich On: Mon Feb 27, 2006 8:17 pm

Mad...your link is dead. I agree...I always thought a tube going thru the top of the firebox would enhance BTU's but I am certainly no engineer! Interesting question tho...maybe our friend from Leisure Line could give us the straight skinny.

Re: Heat Exchange Improvements

PostBy: LsFarm On: Mon Feb 27, 2006 8:30 pm

Can you remove/unbolt the top plate exposing the top plate of the fire box? If so measure the gap and get some aluminum channel, angle or 'I' stock and make several passageways. Bolt the top back on and see if you can detect any improvement.

I'm betting you will. As for the sides, that may be more difficult, since you don't have a second layer with an air gap, and gravity would be working against you for any aluminum pieces and passageways. You could weld some bolts to the sides, and using spacers, add a side plate for an air passageway.
Can you post some photos??

Just some thoughts, Greg L
Stoker Coal Boiler: Axeman Anderson 260
Hand Fed Coal Boiler: Self-built 'Big Bertha' SS Boiler
Baseburners & Antiques: Keystone 11, Art Garland

Re: Heat Exchange Improvements

PostBy: Jerry & Karen On: Mon Feb 27, 2006 8:30 pm

If you guys get a chance to look real close at our hyfire stove, you will see 2 small 2x4 rect. near the top of the unit. They are covering up 2 heat exchangers that run through the body of the stove. If you want the extremely hot air to come out, pop off the caps, if you want more air up stairs, jacket or duct top, leave them in place. I cant say if they make the stove more effic.
Jerry & Karen

Re: Heat Exchange Improvements

PostBy: WNY On: Mon Feb 27, 2006 8:31 pm

Drop the period...hmmm. interesting.
**Broken Link(s) Removed**Ours is all welded together! :(

I was thinking putting some firebrick around the ash box in the bottom along the side to keep it hotter...
Hot Air Coal Stoker Stove: Keystoker 90K, Leisure Line Hyfire I
Coal Size/Type: Rice
Stove/Furnace Make: Keystoker, LL & CoalTrol
Stove/Furnace Model: 90K, Hyfire I, VF3000 Soon

Re: Heat Exchange Improvements

PostBy: AL-53 On: Mon Feb 27, 2006 8:34 pm


My old Alaska is the same way....15 years old..so design is still the same....I think there would be a better way to transfer the heat instead of having the blower blow across the top area ...the heat on the sides seem wasted energy..just some radiant heat at most...


Re: Heat Exchange Improvements

PostBy: madrmc On: Mon Feb 27, 2006 10:16 pm

Thanks for all the responses!

Sorry I included an uneeded period in the link. Should be
**Broken Link(s) Removed**
Greg, as far as the sides (I’ll try to describe as best as I can) I was thinking of welding a box without a bottom (the bottomless side facing the stove) on each side of the stove but first filling it with aluminum fins that would make direct contact with the stove when attached.

It would have a hole in the box pointing towards the back of the stove to hook up to duct work which would run to the back of the stove (from each side), to a T pipe to get the two duct work pieces down to one which could be force fed with a squirrel cage blower. At the front of the stove, I would cut out the side of the box you'd see from the front of the stove. The squirrel cage would force air through the conduction heated aluminum and out the front of the box (now cut out). Getting this fastened to the stove might be the trickiest part.

Dave’s idea of a tube going through the firebox would be an internal heat exchanger and might be the most efficient. I don’t think you’d have to clean it much as fly ash shouldn’t build up much near the top.

I’d try to get some pictures out here, but I’d have to take the top off and I can’t do that with it running.

Stove/Furnace Make: Alaska
Stove/Furnace Model: Channing III