Our pool in the UK (Chilterns) is heat-pump heated but we don’t expect it to work in the winter! Our rule of thumb is when overnight temps start to stay above 10, we turn it on. that’s usually about May. When they drop again below 10, we turn it off. That’s usually the end of September, or, when we come for our Autumn visit to France.
When it’s colder than 10 overnight, it starts to be too expensive to fight off the water temp drops. The heat pump will then be running pretty much all day, and the direct link to my wallet is palpable!
Here in France we’re looking for a small unit but only to extend our season. In the summer it gets quite warm enough from the sun, easily sits between 25 and 28. (Over 28, we stop putting the cover on at night!)
The HPs given in the original reply to your query are rated for 7-35 degrees.
ANY heat pump will be more efficient in warmer air, of course! I would recommend arranging it so it only runs during the day.
You do need to carefully size the unit against your demand. You say you’re in a cold area - what are your typical day and night temps? Do you use a solar cover?
In high summer we get temps up to 30 here, sometimes even a lot more. 35 was typical in this year’s heatwave. And overnights can stay as high as 25. In that period, it gets MORE than enough direct solar heat. Spring and Autumn… well yesterday we had 25-28 in the afternoon but overnights were 8-9. The pool is down to under 20 degs which is a tad brisk!! It’s for this time of year we’re looking to supplement the basic solar. It’s annoying to have the pool here and to only get to use it during our summer visit!!!