Step 2: Divide your Surface Area by 3 (Surface area/ 3) This answer is the minimal BTU size recommended for that particular surface area. Continuing the example above with the 15 x 30 pool, after dividing by 3, you get 150. Therefore, the minimum size heater that is recommended for a 15 x 30 pool is 150,000 BTUs.Click to see full answer. Furthermore, what size heater do I need for a 30000 gallon pool? Heat Pump Sizing Chart – Inground Pools Pool Size (Feet) Summer 4 BTU’s Spring & Fall 5 BTU’s Up To 15,000 Gallons 14′ x 28′ 85,000 BTU 85,000 BTU Up To 20,000 Gallons 16′ x 32′ 85,000 BTU 110,000 BTU Up To 25,000 Gallons 18′ x 36′ 110,000 BTU 125,000 BTU Up To 30,000 Gallons 20′ x 40′ 125,000 BTU 150,000 BTU One may also ask, how long do pool heaters usually last? 7-10 years Also to know is, can a pool heater be too big? A pool heater can be undersized: if it cannot replace the heat lost through evaporative cooling, the pool’s temperature will fall below the ideal. However, there is no such thing as oversizing a pool heater. The larger the heater’s output, the faster it heats the water in the pool, and it will not begin short-cycling.How many kw does it take to heat a pool?You can figure about 5,000 watts or 5 kilowatts per hour per 100,000 BTU’s for a heat pump. For a typical 100,000 BTU heat pump, that’s 5 kilowatts per hour. The national average for Electricity runs $. 13 cents per kilowatt hour.