Heat Pump + 2nd heat source for spa?


Active member
Feb 13, 2021
Hi there,
We are building a pool with an attached spa and right now the builder has priced out a Hayward 140,000 BTU heat pump. We are thinking we need a secondary heat source for the spa in the cooler months and to give the heat pump a boost in the winter if we need to get the pool water temperature up. We live in South Florida (Sarasota), but it does get cooler in the winter.

Our options would be to install a propane tank and gas heater...this gets pricey with the start-up costs since the cost to install the propane tank is approx. $5500 for a 500 gallon tank plus $2600 for the Hayward 250,000 BTU gas heater.

Would a resistance electric heater be a good alternative or do we just need to bite the bullet on burying a propane tank?

Any advice would be greatly appreciated!
Last edited:


Gold Supporter
May 11, 2021
Randolph, NJ
In the cooler months the average temperature is 72-74, but we can have stretches in the high 50s and 60s.
With air temp of 50F, RH of 63% and water temp of 80F a 140k (nominal) BTU heat pump will deliver about 85k BTU and will be abou 4x more efficient than an electrical resistive heater.

Higher air temp, higher humidity and/or lower water temp will make it more efficient while lower air temp, lower humidity and higher water temp will make it less efficient.

This is the Hayward brochure for heat pumps:



Jul 2, 2020
Pittsburgh, PA
If your coldest months, which seems to be Dec & Jan average 74 and 72 daytime, and 55 and 53F evening, I don't think your pool would need supplemental heating from a gas heater if you cover your pool when not using it during colder months. As for heating the spa, it may be a challenge for one HP to get both to good temps. The propane gas heater route will already cost approx $8K. For that cost, you could get extra 140K heatpump (or two for that matter), and not have to pay insane propane prices, as propane is the most expensive way to heat, much more than gas, which is more than HP.

Not sure how big your pool will be, but I would suggest the 140K BTU Raypak 8450 or 8450ti-E-HC (heat/cool). The 5450ti, 6450ti, 8450ti, 6450ti-E-HC, 8450ti-E-HC all support running 2 or more HP units together, one being the master, the other(s) being the slave units. It's built automation. Being FL, you may want the 8450 Heatcool unit, and a benefit of that HC model is it has hot gas defrost, which will help it heat better at lower temps at or below 50F, since it can defrost the coil more quickly. I will say this, the 8450 (and 6450 and 5450) are large units, approx. 3'x3'x4'. But they are super quiet, quieter than my actual 1.5 HP Superpump. If you have the room, then noise isn't a factor here.

I have the Raypak 8450 140K BTU model on my inground 33K gallon pool with a solar cover. I am in Pittsburgh PA. I finished wiring and turned it on Monday 6/14 @ 9pm. Current water temp showed 72F on the HP. I ran it all night, and this morning (6/15) it showed 79F. When we went swimming on Tuesday 6/14 in the afteroon. Water temp showed 81F. The air temp last night dipped to about 58F, and it peaked around 72F on Tuesday, which is fairly cool for June actually. Last couple days air temp peaked at 72F & windy, and nights it dipped to mid 50's and 47F respectively. While I didn't run it at night at all except for the first night, my water temp is showing 85F right now, and I haven't run it since last evening. I am almost thinking I should've gotten the Heatcool model also!

All that to say, is that it worked very well heating my 33K gallon, even in lower temps, around 0.7F per hour. In higher temps, it will probably achieve 1F per hour. With two, it would be double that. Hmm...that's giving me ideas! ;)


Gold Supporter
TFP Guide
Jun 7, 2017
Damascus, MD
What temp do you want your spa? Heat pump generally will never produce enough heat for a spa especially in shoulder months. And unless you keep your pump and spillover on 100% of the time you'll just move that heat into the pool. I think gas realistically is your only choice here.


Jul 2, 2020
Pittsburgh, PA
I think a propane heater is the best choice if cost is no object. I do think regardless, if the spa is a spillover type, it would make sense to be able to turn that off in the winter to maximize spa heating.

However, if that was me, I would be balking at the huge $8k upfront cost, and likely very high operating costs. I still think an extra HP (or two) would still be the cost effective choice in FL. It would make sense to plumb it flexibly, so that both HP's can heat the spa at the same time, when extra heating is needed, or split heating duties between pool and spa. Granted there is the cost to run extra electrical capacity, but if you're already running conduit, you can run a 2nd conduit and wires for not much more than basically the cost of materials. Or one larger capacity set of wires.

If this was a Northern state, agree that a normal HP wouldn't work so well. They could also consider something like the Aquacal Superquiet Icebreaker, which is supposed to heat even at freezing temps, so the coil won't ice up and give problems like non heat cool or power defrost model. But since it really doesn't freeze down there, not sure that is much benefit.
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