My wife and I build a new pool this year, with spa. (My last house had a pool with no spa, so the spa part is pretty new to me).
Anyway, it was great in the summer, turn it on, it heats up - great. But now that winter is arriving, I'm having trouble getting it hot enough. I have the thermostat set to 103, but once daytime temps starting dropping to the 70s, my spa would only heat up to 99 or so (on colder days only 95).
Well last night when the temperatures dipped down below 50, I wanted to heat up the spa and it only got up to about 92.
My question is: Is this 'normal' behavior? or should I expect to get that thing up to 104 in the dead of winter? (I mean, it's reasonable to me that it has a harder time heating when it gets cold out, but I want to know if everyone lives with this, or does it mean my heater is undersized?)
Equipment wise: My heater is a Pentair 400k btu unit, and I don't know the exact size of my spa. It holds 8 comfortably. It has a lot more surface area though because it spills over on all 4 sides (or it does when the pool is running. No spill over when heating the spa obviously).