Dear Mr. Ambrosini:
Thank you for writing to us. I hope that you and your family are well. The AT 6500-A had 48,000 BTU's at 4.3 efficiency according to the old PHPMA rating book from 9 years ago. The higher the efficiency the lower the electric bill. That is a low efficiency heater. You have 19,000 plus gallons on a 27 foot round pool, so that heater is too small for your size pool. Your pool is about 30% bigger in gallons than your friends. We like to see at least 70,000 plus BTU heaters on your size pool using a blanket on the water at night and even higher BTU's if you hate pool covers. That is not an exact rule as the months that you run the heater, where you live, wind speed, if you have a spill over spa, etc effect the heat pump sizing. That heater for sure is too small. I am not a big fan of moving really old heaters too unless I am the one who packs it up. Stuff starts to happen after they have sat for years in the same spot and then you take it on a bumpy pick up truck ride without supporting some components. If you tell us more about your situation we can help you pick out just the right size.