Hot Tub Water Heating Options

KenZ71
KenZ71 Solar Expert Posts: 58 ✭✭
in General Solar Power Topics #1
Ok, not entirely solar power related but there are a lot of knowledgeable people who share opinions so lets hear some thoughts

So a few months I helped a friend move a six person hot tub that she found free on craigslist. She is a tinker, likes to fix things up. So, in trade for helping schlep the big tub I was given a smaller tub.

So, I now have a 225 Gallon Hot Tub with a 20 amp / 120 volt electric heater. There must be better options to heat this thing. It currently takes an hour to raise the temp 4 degrees.

25 feet away I have a Natural Gas fed water heater for the house. Should I convert the tub to Nat Gas? Convert to a 220 Volt electric heater? Solar rooftop water heater?

I've seen posts in the past saying just about all of these are bad ideas. Which is the least bad?

Thanks!
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Comments

  • oil pan 4
    oil pan 4 Solar Expert Posts: 767 ✭✭✭✭
    #2
    Re: Hot Tub Water Heating Options

    I wouldn't even do solar hot water heater in NM because it has managed to get below 0'F for 3 of the last 3 years. (so much for the promise of global warming)
    I would say figure out a way to use natural gas heating since most electrical power is generated by burning something so might as well burn that something at the point of use in turn using that fuel with far greater speed and efficiency compared to burning it for electrical power generation.

    You could use a solar heater during warmer months. I would say drain out the water and put the system in cold storage during the cooler months.
    I would say trying to use solar heat year round would be the worst option, with likely catastrophic failure from freezing during the winter.
    Using the 120 volt heater is the second worst option, because it sounds like it barely works.
    Going to 220 volt heater elements and converting the heater system to 220 might be the cheapest easiest thing to make it warm up faster.
    Natural gas heating would be the cheapest to operate.

    Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

    Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

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  • solarvic
    solarvic Solar Expert Posts: 1,071 ✭✭✭✭
    #3
    Re: Hot Tub Water Heating Options

    I would use a natural gas water heater to heat the hot tub. Most of the components can be bought from ebay and a reputable outside wood stove dealer. You would need a brass circulater pump, water to water heat exchanger and insulated pipe that is used on these outside wood boilers.. centralboiler.com is a good place to get some ideas on what is needed as they have some examples. With a outside wood boiler you can circulate hot water thru a heat exchanger to a waterheater inline before the hot water circulates thru a heatexchanger in your furnace back to the wood furnace.
    Instead of using an outside boiler you would use the waterheater to circulate hot water to a water to water heat exchanger at the hot tub. You should be able to use the circulater pump that is in the hot tub to circulate water thru the other side of the heat exchanger. Since I don,t know much about hot tubs you will have to figure this out but this is a concept that should work. The thermostat at the waterheater will control waterheater. The thermostat that controls the heating element on the hot tub could control when the hot tub circulater pump needs to run. If you decide to do this make sure you get the insulated pipe that you bury for the outside furnace. The cenpex that a central boiler dealer sells is good. It cost at least $10.00 per foot. If you chintz on this pipe you will lose too much heat. A hot tub uses lots of electric. My neighbor ( my daughter) has one with an electric meter on it and they figure it uses about $50.00 worth of electric per month with a 9 cent kwh price. Solarvic
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  • oil pan 4
    oil pan 4 Solar Expert Posts: 767 ✭✭✭✭
    #4
    Re: Hot Tub Water Heating Options

    I didn't even think of that. Use your hot water heater as the natural gas heat source (if you have one).
    I think tapping into the hot water heater could cost the least out of all proposed options.

    Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

    Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

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  • KenZ71
    KenZ71 Solar Expert Posts: 58 ✭✭
    #5
    Re: Hot Tub Water Heating Options

    Thanks for the ideas. Currently I have a 10 year old gas boiler to heat the house via forced hot water with one zone going to a 80 Gallon tank for hot water.

    Last winter I got a quote of $5,000 to add a zone for basement heat. They told me had to swap a control board on the boiler as I was out of zones. So, maybe I should ditch the current tank and go with a stand a lone gas water heater and repurpose the existing tank with a heat exchanger built in for tub heating. Hmmm, gotta think about this. The friend I got the tub from is also good with plumbing so I need get our heads together.
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