Gas Heater w/ Standalone Spa?


Bronze Supporter
Oct 20, 2017
South-Central WI
Buying a house with a standalone spa January 31st. Plan is to use it pretty much year-round (except super hot summer days). Not sure the model, but it seems to be a "typical" standalone spa, 5 person, 240 volt. Connected to a 50 amp breaker. I'll know more details at the end of the month when we close and I inspect the spa in detail and get it running.

I know these are pretty well insulated. What's the typical energy usage (kWh/month) of these? Would there be a potential savings in modding in a gas spa heater instead of using the electric heater?

Our current utility rates, including all distribution fees and taxes, but excluding fixed monthly customer costs, are:
  • Electric: $0.12/kWh
  • Gas: $0.61/therm, or $0.021/kWh
    • Assuming 80% efficient gas heater, and not counting thermal losses pumping through an external gas heater, that would work out to $0.026/kWh for gas heat, or 4.5x cheaper than electric per unit energy
Certainly, gas wins from an cost per unit energy perspective, but the question is the cost of adding in a gas heater, the challenge of modding that to a standalone spa, and what the actual typical energy usage of a standalone spa used year round in Wisconsin is, to compare to the average lifespan of a heater, gas line installation cost (DIY, though that still isn't cheap), additional hassel, etc. Thoughts? Once I get the house I could borrow a power meter from work to monitor what the actual power usage is on a typical weekend.

I suppose this also makes more sense if I would already have a gas heater for a pool, but at this point I doubt I'd want to pay to heat our (future) pool, especially as it will be a non-insulated Intex AGP. I think the most I'd want to pay to heat the Intex is solar panels, but we'll see once we get a pool.

P.S. Because I love entertaining various far-fetched ideas, has anyone ever considered using or used domestic solar hot water panels to heat a spa? I'm not talking pool solar heaters, which wouldn't work in the winter, but specifically high quality domestic solar water panels, that can produce domestic hot water on a sunny day when the ambient temp is at or below freezing. This route would use the solar panels when possible, with electric (or gas) heat supplementing as needed. Certainly wouldn't be the easiest project, as you'd need anti-freeze in the panels for nights and sun-less days, with a heat exchanger to transfer heat from the anti-freeze into the spa, a separate pump for the anti-freeze circuit, a control to turn on and off the pump based on spa temp and panel temp, etc. It would be an interesting, math-filled project though, and I do like projects and don't mind math...


Gold Supporter
TFP Guide
Jul 21, 2013
Northern NJ
A few things you are missing in your energy analysis:

- Many spas use recovered heat from the circulation pumps to heat the water
- Covered spas are very well insulated and lose little heat, and thus use little energy to heat, when not in use
- So the only heating energy use may be for an hour or two per day, at most, of heating when the cover is off in use.

I doubt your cost benefit will work out but if you give it a try let us know what you learn.


Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
Bedford, TX

I have a three person, 240 volt, 200 gal standalone spa and it does not even have an effect on our electrical bill.

I use my EasyTouch to control the temperature of the spa.. It runs about 91 degrees for most of the time and 104 degrees during the two hour period we normally use it.. Even in the dead of winter, the heater is only on for a total of less then 2 hours a day.

Granted, our winters are not like yours, but even so,I can't see much of an advantage to trying to use your gas heater.


Jim R.


Bronze Supporter
Oct 20, 2017
South-Central WI
Thanks. My gut feeling is I agree with both of you, that a gas heater would not make financial sense. Of course the power can be reduced by lowering the water temp, but there's a tradeoff between that and the time it takes to get hot enough to use as well maintaining enough of a temperature to provide freeze insurance if the power goes out.

My first order of business once we get the house should probably be checking how much insulation it has and beefing that up if the answer is not much. I can borrow a FLIR camera from work to help with that.

Current owner doesn't use it in the winter (I almost asked WHY NOT?), but keeps it at 80 °F to avoid freezing rather than draining. I should have asked what his power bill typically is. I'll find out soon enough anyhow, I suppose.