What is the ideal size heater for a 50,000 gallon pool? 300,000 - 350,000 BTU 50% 550,000 - 600,000 BTU 50% Get Free Quotes Today! Question: What is the ideal size heater for a 50,000 gallon pool? Top Answer (50% of 2 votes): 550,000 - 600,000 BTU. Answer: 550,000 - 600,000 BTU Explanation: With this much water you need a very large heater. Precision Pools and Construction WV Get Free Quotes Today! Find Local Pros Free Pool Heater Installation Cost Estimates Related Questions How Much Does Pool Heater Installation Cost? How Much Does a Gas Pool Heater Cost? How Long Does a Pool Heat Pump Typically Last?Top answer: Five to ten years How Long Does a Gas Pool Heater Typically Last?Top answer: 5-10 years Can you add a heater to an existing pool?Top answer: In most cases