Using "wasted heat" from 3" pellet stove exhaust

[kenora]

I've noticed that the exhaust gas from my pellet stove is pretty hot (duh)... anyway the other day I noted that the snow and ice on a metal frame (equipment base) that was beside the exhaust was warm, despite it being -2f. This was from the exhaust blowing on or just near it for a couple hours while I brought my shop from 50f to 65f.

This struck me as a potential heat source.

I was wondering if anyone has built a heat sink or copper coil that the exhaust would blow over...I was thinking that one might circulate water/anti-freeze solution through the coil (heat sink) and then into a receptacle in the house (or in my case shop) that could store that heat and then use it when the stove was off.. so use the heat from the stove when needed and heat from the tank when the stove is off....

I've got a 250 gal plastic tank (in a tote)..I was thinking if I could drive the temp up to 100-110 f it would be easy to create a simple pump/radiator system in the shop that draws from that heat.. this would create a much longer time between heat cycles for the stove....

just wondering who has built one...I'm gonna try!

edit... I KNOW it would have to be seperate from the exhaust... say a coil in a box that the exhaust blew through... my exhaust is straight out with a 45 degree downspout.. total length about 48"

 

[Dataman]

https://permies.com/t/20798/capture-heat-pellet-stove-flue

 

[Washed-Up]

I'm sure its possible to build a liquid convective system to store the heat. I've seen copper water coils that attach to the sides of Harman stoves...so why not something for the exhaust.

 

[maple1]

Did you actually measure the exhaust temperature?

Not sure this is a good idea. It goes too low & you get condensation happening in the exhaust stream. And I think you would be a long time heating 250 gallons of water even just to 100f.

 

[kenora]

Maple1....Nope..I haven't measured the exhaust temp...but...its too hot to keep my hand i/f/o it for more than a few seconds so....maybe 150f... and the water would be at room temp anyway (50f to start)... even if it took a week to heat it up then it would take a week to deplete it....(I think)! As long as its warmer than the air in the shop then I can extract heat from it...(I think)!

Dataman... thanks for the link...reading now

 

[kenora]

Interesting read but not quite what I have in mind...

I'm going to put a loop of 1/2" PEX say 50 ft or so into the tank hooked to a small pump and a car radiator with electric fan as output.

On the input side I'm looking for a roll of flexible 1/2" copper or similar but it's gotta be metal to withstand being in the exhaust blast.

Then put as tight a loop of pipe into a box (covered at the top) that the exhaust blows into...a small pump and an open loop circulation system running into the same tank.. antifreeze in that system, insulated pipes (except in the heat box) and some kind of way to move the box into place and away from the exhaust to clean the stove pipe periodically.

This should have no effect on ash buildup in the exhaust pipe since its "close to" but not on or obstructing the exhaust... gotta start searching kijiji for copper

 

[Ssyko]

Most have just used single wall pipe and coil copper around the outside. Some have converted the stove into a boiler. Lots of videos on you tube

 

[maple1]

I think you will be disappointed with results, but good luck!

 

[zrock]

Will take a week to heat the water up and a day to cool it down.. Stove will have to be run 24/7 and once you start pumping water it will not be able to keep the water up to temp. The area you create for piping will accumulate ash fairly quick due to the effect your box and piping will have on the air flow creating a circular effect with the air flow.

 

[rickwai]

I think you would struggle to get enough heat out to even pay for the copper and material.

 

[Jake86]

What's the length of your exhaust piping before exiting the outside? (Inside vent piping length)

 

[kenora]

The exhaust pipe.. 3 inch duravent is about 12 inches before the thimble and another 18 inches ouside

Sent from my SM-G950W using Tapatalk

 

[Ssyko]

This is the same theory only with a Woodstove and much higher stack temperatures. I did this same thing to heat a pool. Sorry to say it was a huge failure. Check out youtubes on the subject you will get alot of good info. I don’t think you will reclaim enough from 3 foot stove pipe to make a significant difference.

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[Jake86]

Too short for my idea: extract heat from interior pipe by using metal tape wrapped around accordion style making heat fins...a heat sink to extract heat to the interior living space. 12" is probably not enough length to make it worth the trouble.