Pool Heater Sizing & Buying Guide
Determine the exact BTU requirements for your pool and compare gas heaters, propane heaters, and electric heat pumps.
A pool heater extends your swimming season and increases the overall enjoyment of your pool investment. However, choosing the wrong type or an undersized heater can lead to high energy bills and lukewarm water. This guide breaks down the three main types of heaters and how to size them.
Types of Pool Heaters
1. Natural Gas & Propane Heaters
Gas heaters use combustion to quickly heat the water. They are the fastest heating option and work regardless of the outside air temperature. This makes them ideal for quickly heating a spa or for pools in colder climates. Natural gas requires a dedicated gas line, while propane requires a storage tank.
2. Electric Heat Pumps
Heat pumps don't generate heat directly; instead, they capture ambient heat from the air and transfer it to the water. They are incredibly energy-efficient (costing much less to operate than gas heaters) but are slower to heat the water and lose efficiency when air temperatures drop below 50°F.
How to Size a Pool Heater (BTUs)
Pool heaters are rated in BTUs (British Thermal Units). While the exact requirement depends on factors like wind exposure and whether you use a solar cover, a standard rule of thumb for gas heaters is:
- 100,000 BTUs for every 10,000 gallons of water.
- Example: A 20,000-gallon pool should ideally use a 200,000 to 250,000 BTU heater.
- If you want to heat a connected spa quickly (e.g., in 30 minutes), you will likely need a 400,000 BTU heater regardless of pool size.