mamasproject said:

I vote for the gas heater too! The heat pump will cost you $2000 more than the gas heater! If you only use the pool on weekends or a day here or there why would you want to waste all that energy heating a pool nobody is using????

Our pool heater raises our pool 2 degrees per hour and uses 4 gallons of propane per hour. We have turned it on a total of 4 times this year!

Using your example, an 8 degree rise will take 4 hours and $44 worth of propane. A typical heat pump this time of year will put out ~60,000 BTU an hour. On a 20,000 gallon pool, it would take ~22 hours to raise it 8 degrees. At $0.15 per kW/hr (your may be more or less, $0.15 is what mine is with taxes, transmission, etc), you will spend ~$6.60 to run it. Add another 8 hours of pump run time and the total cost is maybe $7.00. Thats ~7 times cheaper. You could run the HP and filter pump 24/7 for a month to maintain the pool temp for ~$220 per month. That same $220 will run a gas heater maybe 18-20 hours total.

Now, that being said, the rains we got last week (we got the same soakers here in massachusetts) really reduce the output of a heat pump. All that cold rain really disapates the heat from the heat exchanger and reduces the BTU put into the pool, I'll grant you. When the cool weather and rain started on sunday, my pool was at 85 degrees. On monday morning, even with the solar cover, it went to 79. My heat pump ran 12 hours a day (7 am to 7 pm) from monday morning to yesterday, so 4 days basically. At the end of each day, the temp of the pool was 83 degrees. It did take 12 hours to put in about 4 degrees a day to maintain it. Thats 12 hours for 4 days so that 48 hours of run time. So over that 4 days, that's ~$20 to keep it running for 12 hr/day for 4 days. If I did'nt heat it for those 4 days at all, and let it get down to 72 (which is where i figure it would have been) that would be 11 degrees to get it back to 83. With LP, it would take 4 hours and 16 gallons (~$44) to heat the pool (LP in my area is $2.75/gallon. Much faster, but still double the price.

Now, that all said, sometimes I'm frustrated too with the speed that a heat pump works, and the fact on rainy days the BTU output is really, really low. I do wish the heat pump industry would put out realistic numbers for BTU output. It's difficult since ambient conditions can change it pretty drastically. But, the COP numbers that are based on 80 degree ambient temp and 80% humidity are not realistic. I've even considered adding a 250,000 BTU LP heater as a supplement for my HP when I get frustrated, but when I run the numbers, it still doesnt make sense as much as you might think it does.

Tim, natural gas is another animal all together. A NG heater is much cheaper to run that a LP heater. For comparison, a gallon of propane is about equal to a therm of NG in terms of BTU output (~100,000). The average cost of a therm of NG is $1.00 (mine is $0.77) and the average cost of LP is $3.00 (mine is $2.75). So, a 400,000 BTU NG heater costs about $4.00 per hour to run and a 400,000 BTU LP heater costs $11 dollars to run; almost 3 times. A Heat pump cost about $0.55, but puts out less BTU per hour.

As mentioned above, you also need to take into account how you use the pool. if you use it only on weekends, maybe gas is the way to go. We use ours 4-5 days a week, sometimes everyday. For me, LP doesnt make much sense. Electric rates are cheap too. If you live in cali where they are $0.40 /kW/hr, then gas might make more sense. In the end, gas vs HP depends on a number of factors.