Dear Mr. Hope
Thank you for added information.
For pools that are 27' round, 17,000 gallons or about 64,000 liters, then I would look at heat pumps in the 100,000+ BTU range. I would rather go too big than have a heat pump that is too small and have you be disappointed in the heater's performance. Since you do use a solar cover, then an 85,000 BTU heat pump would be fine.
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