We have a 7-10,000 gallon in-ground, gunnite/plaster pool. We are adding a heater and have decided to use a heat exchanger, rather than a gas heater. Heating is not necessary between June 1 and mid-to-late September (80 degree pool temp without heater). Any opinions about a Heliocol vs. Pentair heat exchanger? Both would be 125,000 BTU. Heliocol salesman says Pentairs do not function well when temperature drops below 55 degrees - so might not work during March, October and November. We will also change a single speed Pentair filter pump (2 HP) to a Pentair Intelliflo, and have been offered both the VS+ (3 HP), and the i2 (2 HP). Thanks for any help.