The options are somewhat dependent on your goal.

IMHO, you are too far North to use a heat pump. The same is true for solar. That leaves gas, be it natural gas or propane.

Water is heated differently than air. The formula for heating water is one BTU is needed to heat one pound of water one degree F. There are 8 pounds in one gallon (about 4 liters). That means to raise the pool temperature from 79 to 80 F, it would take a touch over 200,000 BTUs of heat energy. For your pool, that would take a 400,000 BTU unit a little over a 1/2 hour (with losses) per degree.

Pools lose their heat primarily from the surface evaporation. Cover the pool to prevent that and your nightly loss from the cooler nights will drop from roughly 5 degrees F to about 1 or 2. Reheating is expensive and time consuming. This makes heat pumps and solar inefficient and terribly slow, especially when it's cooler out..

Gas heaters don't care if its 40 degrees F or 85 degrees F out. They work with the same efficiency where a heat pump will lose its efficiency as the temperature drops. Gas heaters are the most powerful method. The largest residential heat pump I have seen is 150,000 BTUs, under ideal conditions, and the largest gas heaters designed for residential use are 400,000 BTUs under normal, above freezing conditions.

Solar panels have limitations and gating factors that can make it a possible but unlikely fit. They need sun, a southern exposure, no more than a two story roof, significant roof space, winterizing, aesthetics, slow heating that will likely be exceeded by your losses at night, and availability.

Scott

Hi Scott,
Thanks for you reply.
I'm thinking that something that will heat the pool up slowly, say over a week, and keep it warm (whatever that is) will do. It's very hot here during the day, but it cools down at night. I like the solar idea, and the heat pump, but don't know if they will do the job, as you indicated. I think I'll find out what the pool places are suggesting and go from there.
.... john

We live in Southern NH. We have a 400k BTU propane heater, a heat pump (don't remember the output, but I think it is one of the biggest/bigger ones), and sometimes use a solar cover.

We use the propane heater to get the pool up initially, or if we are having a party and want a warm pool (at about 4:30, the sun is obscured by the trees, and if it isn't really warm out, people get cold).

We use the heat pump after the pool is open to keep the pool at our target temperature (around 84). When the temperature is under 70 for the day, it runs all day, when it is above (depending on the loss at night), it runs for a few hours. In the summer (when it is warm at night), it runs for very little.

The heat pump costs about $8/day to run all day (this includes running our pool pump on high all day, rather then just 3 hours). I electric is $0.16kW/h. (I have meter readers that measure and graph my electricity usage, it is sometimes hard to isolate a given item and its usage, but there is a clear trend that makes it obvious the extra cost of certain things, like the heat pump).

We use the solar cover during our non-peak swim season (May and September). We have the removal and adding down to an art, but it is ugly and messy. Without the cover I go for a 5 minute swim sometimes (I work from home), with the cover, I only go swimming if I am going to be in for a longer period of time (since the overhead of the cover is too much). The cover helps reduce how much the heat pump has to run when the nights are cold and makes a huge difference.

Hi cnr1089,
Thanks for your help.
...... john

Hi:

I'm trying to convince my dh to get us an above ground pool. Since our backyard is mostly shade (we live in MA) we would need to get a gas heater for the pool. I'm curious...for a small, oval above ground pool...what would it cost to heat this...would you know?

Also...how much does it cost to get a gas powered heater?

Thank you....just want an informed decision...

Thanks