how can I heat my water for the home with flu pipe?

I have about 6 foot of single wall flu pipe from my wood heater to the ceiling where it gets into triple wall.I want to wrap coils of 3/8 or 1/2 copper pipe around single wall to get hot water free. Now how would I connect it to my existing hot water heater? Or I can put a 2nd tank outside insulated horizontal and let the water gravity feed into the bottom of the copper coils...would the heat fron flu pipe cause the water to rise up and out into the outside tank?what about the supply of water to the outside tank? concerned about pressure back to water supply line...could use check valve i guess.This system sounds like it should be simple but just want to construct it right and safely, please help thank you so much

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What's a "home with flu pipe"? A continuous flow of chicken noodle soup?
rockytop44 (author)  Lithium Rain8 years ago
with the plethora of answers that I recieved from my question your answer does not in any way add to the answer to the origional question.
It was supposed to be humorous.
I like that. I got da' flu now.
rockytop44 (author)  Re-design8 years ago
we are talking about being totally submerged in hot water, now that would kill that my friend in the north
framistan8 years ago
There are 3 BIG problems with this idea. FIRST... was already answered.. cooling the flue gases will cause excessive creosote buildup on pipes (fire hazard). SECOND -- it can be dangerous if you get water too hot it could make STEAM. I'm not talking about WATER VAPOR like from a tea kettle... STEAM is invisible and VERY VERY HOT. If you breathe it--- it can burn your lungs and kill you. THIRD--- there are OTHER WAYS to heat water using woodstove that will not produce steam. Do a lot of RESEARCH before deciding on which system to build. Try researching at and at for starters.
I think chilling the flue like that is a bad idea, you're going to get creosote and tarring issues if you're not careful. Steve
Yea, but chimney fires are great. Like a jet engine in the living room.
lemonie8 years ago
I think you might be better with a jacket, but you'd have to make one, which is not going to be that easy. W'ref the pipe: I've experimented with things like this and you can get them to self-drive on convection. Wrap in wide bore pipe if you can, use a tank at the top. (I can't guarantee it'll work but I'd be hopeful). L
what diameter tubing did you use?
I was doing something else with an open fire, about 5mm ID but the system did work. The flue is different. L
yes...less heat... and you were using ~1/4" tubing... I'm thinking a flu system, even with the gravity assist, might need a small recirc pump.
Maybe, but I'm thinking of including it in a central-heating loop which I don't think exists... L
seandogue8 years ago
on the face of it, your idea has merit. I'd think you'd want flu pipe that you could mechanically connected to the copper though, to provide a solid conduction path for the the heat. If it's stainless flu, it's possible that you can silver solder the copper tubing to the flu. 1/2 inch pipe might be a bit large to get it to provide a convective drive for the water though, so you might have to augment that with some sort of pump and/or reduce your tubing to a more manageable diameter like 1/4" Seems like you'd need to collect the water in an expansion tank to avoid burst, with a possible need for a relief valve as well. I'd think of it as a preheater or recirculator, rather than a primary source, where you send your feeder line to a tank that sends water thru the parasitic heater, then to the expansion tank and into the water heater, or in the case of a recirculator, from the water heater (if temp < setpoint) thru the coils and back to the expansion tank and into the water heater.
If you could automate the flow path, it could be used in a recirculation mode (like a float charger) during periods without outflow from the system, then automatically switch to preheat mode when flow is present (on the inlet side).
Re-design8 years ago
And you need a way to stop the water in the flue tubing when the flue was not hot. Otherwise it'll just suck the hot out of the main hot water tank.