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Thoughts on heating Hot Tub water with a wood stove?

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by Frank Stevanus, Dec 8, 2011.

  1. Frank Stevanus

    Frank Stevanus New Member

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    I have a Pleasant Hearth with 6 inch flue and I want to heat some hot tub water with the wood stove. I thought about the stainless steel tube in the box, but that voids the warranty and insurance would frown.
    I thought about heating water using the exhaust gases. I have a 6 foot run of single wall pipe that I might put some 3/4 copper tubing either inside or out. Out is safer but I wonder if it would heat the water enough. I also wonder if inside the exhaust would get too hot for the copper? Any thoughts?

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  2. Battenkiller

    Battenkiller Minister of Fire

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    Sounds like a hippie Magic Heat to me.
  3. mellow

    mellow Resident Stove Connoisseur

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  4. woodchip

    woodchip Minister of Fire

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    Someone I know a while back used an old woodburner with a back boiler set up outside to heat their hot tub.

    It was very successful, in fact too good.

    I seem to remember it got so hot nobody could stay in the thing for long........ ;-)
  5. burleymike

    burleymike Feeling the Heat

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    I actually have toyed with the idea of running a coil of copper on top of the air jacket around my insert and using that hot water for a little rad in the basement. Perhaps you could put a coil on top of your stove and another sheet of steel on the coil if you don't like looking at it. You need to be careful that the coil is not sitting directly on the top of the stove, you need a small air space. Stove top temps can get hot enough to really make the water in the coil too hot. I would imagine it would be hard to control the temperature, if the hot tub water gets too hot it can damage the tub or pump.

    Your best bet is a dedicated stove for the hot tub so you can give it enough fuel to heat the water and not overheat the water.
  6. Battenkiller

    Battenkiller Minister of Fire

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    Is this the guy?

    [​IMG]
  7. woodchip

    woodchip Minister of Fire

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    Certainly looks like he's gonna cook the same way ;-)
  8. roknwoe

    roknwoe New Member

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    To: Frank S

    I too have considered "how to heat water" from my basement WoodChuck add on wood furnace. Currently my monthly natural gas bill is about $30 per month for the wife and myself in summer months...for a natural gas range and the natural gas hot water heater.

    However, if we were to have an outdoor hot tub or indoor whirl pool tub, it would be more tempting to get serious about this idea. A good friend of mine who owned a super insulated (outside installed) Premier 6 person hot tub, informed me it only cost him about $30 per month to heat the hot tub water (Central Wisconsin) with gas (I believe it was propane).

    Running a basement wood stove in the summer to heat up extra water (to me) would over heat the house when it is already 90+ degrees in the summer. I suppose I could shut off the wood furnace blower, and hopefully it would not overheat the wood furnace? No use heating up the house in the summer, and then running the central air condition to keep it cool, just to save money on hot water heating? (whatever! there is usually a solution to every problem!)

    I have previously searched the Web (Google and YouTube) looking for examples of others who have heated water with a wood stove. Some are way too complicated and expensive, while others were questionable in my opinion for safety reasons. Some (You Tube) were so dark, you could barely make out how they did it. Some were quite nasty...pipes, wires, tank...a hell of a mess of junk all over the place.

    The best illustrated way to do it, I found on Mother Earth News. It was a safe scientific installation with plaster paris surrounding a 50 foot coil of 1/4 inch copper tubing bolted/mounted to the side of a free standing wood stove. They had a separate "tempering tank" conjoined with the primary hot water heater tank. I cant remember if this was via YouTube or a Google search on Wood Stove hot water heater. (cant remember what exactly I searched on). When the time is right, this is the technique I would use to make this happen.

    Good luck to you.

    Gary (Central Wisconsin)
  9. pen

    pen There are some who call me...mod. Staff Member

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    Wood Burner Man, you would probably get better info about this sort of thing from the folks who frequent the "boiler room" on this forum.

    pen
  10. wkpoor

    wkpoor Minister of Fire

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    Go to the Vermont Elm site. Steve has rigged up an Elm to heat water. I haven't studied it myself but it was to supplement a hot water heater. Sounds like it is what you want to do.
  11. begreen

    begreen Mooderator Staff Member

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  12. Jackfre

    Jackfre Member

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    I've done a lot of this back in the day. Used the old Holly Hydro-heater or made the chimney units. As well, I made a bunch of wood fired saunas that worked really well. I built a couple wood fired boilers as well, but when the houses were sold I cut them up. Fear of the trial lawyers association. Regardless of method, you must be aware of the safety issues related to this. On my Dad's wood boiler, I lined up relief valves with sequentially higher ratings. I replaced the lowest rated relief valve annually. Yes, these things make me paranoid. You need a circ as well as an expansion tank. Your piping has to be correct or it will not work, but will trip the relief valve. I also did a lot of solar heating of hot tubs, and those worked well and are an excellent method of hot tub heating. I would never disable the blower on my wood furnace to heat a hot tub. I used to represent Yukon and when you overheat that metal it expands and just, well, you do not want to find out what it does, because your warranty will be out the window and your furnace will be junk.

    In today's world with today's appliances, I do not think it worth the effort to add this capability to a unit unless it was designed to do this job.

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