Tired of 300F going up the chimney

Now THAT'S interesting! I'm interested to see how quickly it gets clogged up with ash. At least with the hose connections, you can remove it easily to blow it out. Sounds like it's really working! As soon as you see the flame getting lazy, clean it out. It might just turn out to be a routine procedure every week or two but well worth the extra heat.

Yeah, the small ports inside with all the U-bends are going to be trapped ash heaven. I wish there was a high temp filter... brain just fired... Install an automaotive catch can? lol

briansol said:

Yeah, the small ports inside with all the U-bends are going to be trapped ash heaven. I wish there was a high temp filter... brain just fired... Install an automaotive catch can? lol

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No u-bends. Straight through. In one side, out the other. When you're done with the intercooler, can I try it on my Grand National? $60 is cheap for a Chinese intercooler.

skibumm100 said:

No u-bends. Straight through. In one side, out the other. When you're done with the intercooler, can I try it on my Grand National? $60 is cheap for a Chinese intercooler.

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so, it's not like an oil cooler/AT cooler?

What about using a large heatsink wrapped around the pipe?

no, air to air coolers use straight through design to maximize air flow and less pressure drop than traditional fluid coolers.

I love the idea of recapturing heat from the exhaust, but won't you lose draft and cause creosote buildup by doing that?

With dropping exhaust temps id start to worry about condensation leading to corrosion leading to exhaust leaks. Dont think intercoolers arr meant to be overly corrosion resistant and pellet exhaust isnt meant to be cool.

After seeing what a magic heat did on pellet venting. You'll need to keep an eye on it and if burned at low temps with condensation you might see creosoot build up..

daffonce said:

With dropping exhaust temps id start to worry about condensation leading to corrosion leading to exhaust leaks. Dont think intercoolers arr meant to be overly corrosion resistant and pellet exhaust isnt meant to be cool.

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Pellet exhaust IS cool compared to wood heater exhaust. Since we are using positive pressure exhaust, we really don't worry or count on natural draft caused by rising heat. Heck my exhaust pipe right at the stove is 160 to 180. If you had the 300 to 400 degree wood heat going up there, you'd have no heat coming from the puny little flame in the burn post into your house. If I get any creosote buildup, it's on my heat exchange tubes.

With enough heat exchangers, a stove could approach 100% efficiency and produce room temp flue gases! But that would lead to a large, heavy and expensive stove!

Great idea, I like it! My stove goes straight out the wall because I did not want to see the piping inside. The stove has about 12" of pipe that I could put a heatsink on to recapture some losses.

Bill

Cool idea. However if the exhaust temperature is to cool you will have to add some kind of drain to remove accumulated condensate or it will leak on the floor or some where in the stove. This is done on high efficacy condensing furnaces and boilers. I would keep it simple, keep the vent temp just hot enough to push out the moister.

tjnamtiw said:

Pellet exhaust IS cool compared to wood heater exhaust. Since we are using positive pressure exhaust, we really don't worry or count on natural draft caused by rising heat. Heck my exhaust pipe right at the stove is 160 to 180. If you had the 300 to 400 degree wood heat going up there, you'd have no heat coming from the puny little flame in the burn post into your house. If I get any creosote buildup, it's on my heat exchange tubes.

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I would double check those temps. On the burn tests I've done on (2) different stoves, flue gas temp ranges between 300 and 380 deg F, on average, measured with a type K thermocouple in the flue gas stream. Is the temperature you're measuring the outside of the double wall pipe?

Great thread topic and experiment! Please keep us posted regarding ash and condensate potential

Flue gases will liquify at temperatures below 250 degrees F. Sounds like playing with fire...pun intended.

skibumm100 said:

I would double check those temps. On the burn tests I've done on (2) different stoves, flue gas temp ranges between 300 and 380 deg F, on average, measured with a type K thermocouple in the flue gas stream. Is the temperature you're measuring the outside of the double wall pipe?

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Nope. It's done with a contact K thermocouple right on the exhaust exit housing from the blower. This is AFTER I made the mods to my stove. If you're measuring 380 degrees, I would guess your heat exchanger isn't 'exchanging' due to build up of ash or your exhaust blower is running too high and not giving your exhaust enough time to exchange heat.

Realize that the temps I took were to measure relative exhaust temps before and after my mods to prove that I was extracting more heat with the mods. We aren't measuring the exact same thing BUT I seriously doubt that there would be a 200 degree delta T between the gases and the steel.

Mr. Spock said:

Flue gases will liquify at temperatures below 250 degrees F. Sounds like playing with fire...pun intended.

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I'd sure love to see your backup on that statement for pellet stove flue gases. On the Bixby stoves, you could stand right outside the house and hold your hand in the exhaust stream, so I'm told.

tjnamtiw said:

I'd sure love to see your backup on that statement for pellet stove flue gases. On the Bixby stoves, you could stand right outside the house and hold your hand in the exhaust stream, so I'm told.

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I would agree that pellet stoves produce much less flue gas. Have to go my computer is going to reboot not by choice ...

https://www.hearth.com/econtent/index.php/articles/creosote_from_wood_burning_causes_and_solutions

Mr. Spock said:

I would agree that pellet stoves produce much less flue gas. Have to go my computer is going to reboot not by choice ...

https://www.hearth.com/econtent/index.php/articles/creosote_from_wood_burning_causes_and_solutions

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The article was clearly written to address wood stoves but this little paragraph says it all >
" You can either keep the chimney above 250 degree F all the way out the top or, you can burn up the gases that form the creosote in the stove before they reach the chimney. Modern stoves do the latter and capture the heat produced by essentially burning the smoke.. This is true of stoves with catalytic converters and non-cat stoves that burn gases by recirculating them. Either way, less smoke means less creosote. Burn the smoke and you burn the gases. No gases, no creosote. As simple as that."
So for a 'modern' pellet stove, I would assume we are doing the latter if we are competent enough to maintain the stove so that it gets the proper fuel/air ratio to burn those gases. There's no way that you are going to keep the flue above 250 all the way up a chimney. I've never seen smoke out the top of my chimney except for the initial light off either.
We have to be careful just spitting out blank statements which newcomers will take as the absolute truth.

tjnamtiw said:

I'd sure love to see your backup on that statement for pellet stove flue gases. On the Bixby stoves, you could stand right outside the house and hold your hand in the exhaust stream, so I'm told.

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In the beginng the double wall Bixby pipe system was a catastrophe. It proved to need a higher grade of SS to prevent pit-holes and leakage of exh back into the fresh air side which prevented a dependable burn. It wasn't bad if you used a 24 or 36 inch out the back and through a wall. But the problem started when people had a stove in the basement and used elbows and longer lengths of pipe. Doing this made the exh cool off way to much and left gunk build up in the pipe. Burning corn compounded this problem as it is more acid then pellets.
People would e-mail me asking why their stove was working so poorly and if they had a long exh run that was their answer. When they dismantled the pipes the inner pipe was full of holes letting exh be sucked into the fresh air intake. I told them to use a multi fuel 3 inch pipe instead of the double pipe then showed them how to modify the Bixby so they could pipe in fresh air separate from the exh solving this problem. There was a lot of money wasted until better SS was used or people changed the system.
5 years ago I bought a 36 inch double wall made for Bixby and the inner pipe has held up great but it is a shorter run and had the upgraded SS inner pipe. As TJ says it is warm but not burn your hand hot.