What size heater do I need for a 15,000 gallon pool? 100,000 - 150,000 BTU 25% 150,000 - 200,000 BTU 25% 200,000 - 250,000 BTU 25% 350,000 - 400,000 BTU 25% Get Free Quotes Today! Question: What size heater do I need for a 15,000 gallon pool? Top Answer (25% of 4 votes): 150,000 - 200,000 BTU. Answer: 150,000 - 200,000 BTU Explanation: This is the most economical for a pool that size Precision Pools and Construction WV Answer: 350,000 - 400,000 BTU Explanation: Also, is there a spa? Available space? NorCal Pool Builders 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