Weighing a booster heater for the spa side vs just leaning on the heat pump

Started by Chuck Weaver · · 4 replies
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#1
When we first moved down from Michigan the house had a spa spillover nobody had used in years, and now that I actually swim every morning I've been trying to figure out the smart way to get that spa hot without waiting forever. One camp says keep it simple, just let the UltraTemp run longer and push harder before soak time. Other camp says a small dedicated booster heater just for the spa side gets you there faster and you're not making the big heat pump work overtime for a few hundred gallons. Mine's been fine running the single heat pump four seasons now for the main pool, but spa recovery time is slower than I'd like on a cool morning. Anybody run a two heater setup, spa booster plus whole pool heat pump, and is it worth the extra equipment pad clutter and the extra thing to maintain. Good luck with it.

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#2
Look, with a spillover the real problem is usually the plumbing split not the heater, if that spa line is only running through a shared heater loop on a small check or gate valve you're starving recovery time no matter what BTU's on it, I'd have somebody look at the valve setup before you buy a second heater.
#3
Dave's onto something there, plumbing is usually the bottleneck before BTUs ever matter. One thing that gets left out though is how heat pumps actually behave with small volume fast calls like a spa, mine on the UltraTemp style unit takes a while to ramp and doesn't love short cycling for spa bursts the way a gas or electric booster does, it's built around steady state heating a big volume slow and efficient not blasting a few hundred gallons on demand. So even with perfect plumbing you're fighting the nature of the equipment a little. Not saying buy a second heater before checking the valve like he said, just don't be shocked if recovery is still sluggish after that fix and the booster conversation comes back around anyway.
#4
I don't run a spillover so no direct experience there, but robotvic's point about heat pumps hating fast small volume calls matches what I see on my own equipment even without a spa, my UltraTemp style unit is happiest doing a slow steady climb on the full 22k gallons and if I ever try to force a quick temp bump it just grinds, COP tanks because it's not built for short cycling, so for a few hundred gallons on demand every morning I'd check the valve first like Dave said but I'd bet money you end up with the booster anyway.
#5
Check the valve before you spend money on a second heater, Dave's right about that. Mine's an attached spa not spillover so different animal, but I run the same deal, one heat pump for everything, and the slow ramp thing is real. Cool morning the spa side takes forever to climb because the heat pump wants to creep up a degree at a time on the whole body of water, it's not thinking "small volume, go fast." I just started it way earlier than I wanted to and lived with it. Never added a booster, wasn't worth the extra thing to maintain and one more thing to leak or fail on the pad for four hundred gallons of spa water.