Pool Heating Math

[CarlD]

Obvious problems:
1) You're not just heating the water, you're heating the walls and the earth around the walls. I don't know how far the heat will penetrate, but 6" to a foot is reasonable. So how many cubic feet of dirt and fiberglass do you have to heat?
2) The BTU content of propane is based on a 100% conversion efficiency. Never gonna get that. I don't know what the maximum efficiency is, but it will be lower. You'll use a lot more propane than you figure.
3) Even if insulated, 50' from the heater to the pool will lose a fair number of BTUS. Gotta figure that, too.
4) Since 3000 gallons is about 15% of 20,000 gallons, your ESTIMATED 16 degrees for the 3000 gallons comes down to about a 2.5 degree rise/hour for the entire 20,000 gallons--my guess.

I don't guarantee my numbers by any means, but.....they are worth thinking about.

[stlbill]

Carl,

Thank you for the reply!

If I do not use propane then I have to use a heat pump, but the largest heat pump I can find is less than 200,000 BTUs at top efficiency and conditions.

My decision is to spend 2X as much for the heater, have a lot more parts to break, but hopefully make back savings on energy with a heat pump - if electric rates do not rise over the life of the heater. I used to own a diesel car thinking that form of energy would be cheaper and paying more for the diesel engine option was a good idea. Ha... wrong!

The pool installer claims he has plenty of unhappy customers with heat pumps because in St. Louis, MO USA there are many days when environmental conditions are not right for a heat pump to work well. I think it has to be above 50 degree or maybe even warmer.

All comments appreciated. Thank you!

[CarlD]

You last point is key and requires an answer to the question: How cold outside are you looking to overcome and actually swim in? For me, in NJ, there's NO WAY I want to go swimming in my pool when it's below 75, much less when it's below 50. For MY needs (and mine alone), I would never use a heat pump to heat my pool when it was in the 40's (that's what below 50 implies). I don't know where the "sweet spot" for heat pumps is, but I don't think it's there.

If, OTOH, you are looking to keep your pool evenly warm and maybe extend your swim season at both the front and back end, that's a different decision tree. I use solar and it allows us to swim, in NJ, usually from early May till late September, rather than than traditional Memorial Day to Labor Day season. For that, a heat pump should EASILY cost far less to run than a gas heater. But if you want to heat and swim in your pool in the 40's and below, then a natural gas heater is probably the cheapest to run, followed by a propane heater.