Heating the water in a pool makes swimming more enjoyable for everyone.
With different types and sizes of heaters available, heat pumps are an energy efficient and effective solution to warming up pool water.
But if you’ve decided to go electric, you’ll need to figure out how to get the correct pool heater pump sizing for your pool.
Important: This article is about sizing electric pool heat pumps, not gas pool heaters. If you’re looking for the latter, please read our article on sizing a pool heater.
Why Is Pool Heat Pump Sizing Important?
A heat pump works by drawing in warm air from the outside environment and injecting it into the pool water.
Measuring output in BTUs, it runs on electricity and therefore takes a longer time to heat your pool when compared to a gas heater.
Note: The British Thermal Unit (BTU) is a unit of measurement that measures thermal (heat) energy. Electric heat pumps have BTU ratings in the range of 50,000 to 150,000. Calculating the amount of BTUs required will help you determine the size of the heater for your pool. Smaller inground pools and above ground pools can get away with using a 50,000 BTU heat pump, but if you have a large pool you’ll need something bigger. A small pump on a large pool means it will be very slow to heat and might not even reach the desired temperature you’re aiming for.
Generally speaking, you should oversize the heat pump as much as possible. You’ll never regret going too big, as doing so means warming the pool at a faster rate without running the heater as much.
With that being said, there are still some things you should consider when sourcing a heater for your pool, so let’s talk about those.
How To Size A Pool Heat Pump
The size of your pool, the outside temperature, humidity level, and the amount of wind will all factor into how fast your heat pump warms the water.
Correctly sizing your heat pump keeps those outside influences from becoming as much of a determining factor in the temperature of your water.
There are 2 ways you can determine the proper pump size:
1. The Easy Way
The chart below shows the general amount of BTUs needed when using a heat pump. This makes it easy to choose a pump that will work with the amount of water in your pool.
| Pool Volume(Gallons) | Heat Output(BTU) |
| 10,000 | 50,000 BTU |
| 15,000 | 90,000 BTU |
| 20,000 | 120,000 BTU |
| 25,000 | 140,000 BTU |
Based on this information, if your pool has 15,000 gallons of water, and you wanted to go with a 120,000 BTU heat pump, you absolutely could. It wouldn’t be overkill, but rather it would heat the water in a shorter period of time.
2. The Precise Way
If you want to be spot on with your heater size, first you need to determine the required increase for your desired temperature.
For this example, we’ll say the pool is sitting at 65°F and we want it to go up to 80°F – an increase of 15°F.
Secondly, you need to find out the surface area of your pool. We’ll use a 16 x 32-foot pool for an overall square footage of 512.
Now, calculate the appropriate values using the following equation:
(Surface Area) x (Temperature Increase) x 12 = (Minimum BTU Needed)
512 x 15 x 12 = 92,160 BTUs
According to these calculations, you’ll need a heat pump that can output at least 92,160 BTUs to increase the temperature in a 16 x 32 pool by 15°F.
For reference, a 16 x 32 pool is roughly around 15,000 gallons of water.
Looking at the chart above, we can see that 15,000 gallon pools require a heat pump with 90,000 BTUs, which is right in line with our 92,160 BTU figure.
Sizing Considerations
If you’re still not sure on the correct size heat pump to go for, ask yourself the following questions:
- How quickly do you need to heat the water? The BTU output of heat pumps ranges anywhere from 50,000 up to 150,000. The higher the level of output, the faster your pool will heat up. If you decide on a middle of the road output like 100,000 BTUs, it will still heat the pool, but it will also take longer.
- Do you have the required electrical? Heat pumps require lots of electricity to run and is one of their main drawbacks, as this can put a sizable dent in your wallet (although they’re still cheaper to run than gas heaters). You should also make sure that you have the proper electrical setup as heat pumps require anywhere from 50 to 60 amps to power.
- What is your desired water temperature? Most pool owners want warm water between 82°F and 86°F. With heat pumps, they can only generate so much heat and will eventually top out (especially smaller pumps) due to their dependence on the outside temperature for the level of BTU output. Generally, though, you should be able to heat your pool to 82°F on warm days.
Other Considerations
With a heat pump, maintaining the warm water temperature can reduce your use of electricity. You should ask yourself the following:
- Are you using a solar cover? A solar cover is a must. Heat mainly escapes the surface of the pool water. Covers trap that heat in so you can get away with using a smaller pump, less often. They also keep water from evaporating so you won’t have to spend more money refilling the pool. Solar covers come in a few variations: a large bubble wrap-like blanket, smaller, interconnectable solar sun rings, or chemical liquid solar covers.
- How often are you swimming? If you want to maximize the heat in your pool and keep your electricity bill low, you should only keep the pool uncovered for about 2 hours per day. Of course, you can use the pool longer, but after 2 hours you’ll have to run the heater to replace the heat that was lost.
- What months are you swimming in? Electric heat pumps work best in warm months. This is because they take warm air from the outside environment and inject it into the water. Traditionally, heat pumps work well from May to September. But once the weather drops to around 50°F, running them will be pointless as there’s not enough warmth in the air to transfer to the water.
- How much are you willing to pay? Pool heat pumps are much cheaper to run than gas pool heaters (by about half), but they also cost a lot more upfront. Not only that, if you live in an area where electricity is expensive, a heat pump might not be the most cost efficient option.
Size Really Does Matter
As with all pool heaters, if you go big, you’re golden.
A smaller pool heater pump size won’t necessarily be detrimental, but you’ll have to run it longer and may have problems keeping the pool warm.
Using the chart or calculation method above, you can figure out the minimum heat pump size your pool requires, and if you want, you can go bigger for faster heat times.
