What Size Pool Heater Do I Need? – (Updated 2021)

Pool heaters allow you to open your pool earlier in the spring and the swimming season can be extended well into the fall, but they are a large investment so before deciding to buy a pool heater, you should spend some time researching.

Pool Heater Sizing

If you don’t select the size of your pool heater carefully, you can be spending a lot of money and time down the line.

Things You Need to Consider for Pool Heater Sizing

Before you buy a pool heater there are some basic things that you need to consider –

  • Size of the pool and pool heater sizing

  • Your heating needs and preferences

  • BTU needs

  • Whether or not you use solar cover

  • Environmental considerations

pool heater sizing calculator

1. Size of The Pool

The bigger your pool, the more powerful heater you will need, so you need to calculate the volume of your pool. First you have to find the surface area and then multiply it by the average depth.

what size pool heater do i need

To find the surface area- Water Heater Sizing

  • Square and rectangular pools – just multiply length by width.

  • L shaped pool- break the pool into two rectangles and then multiply Length and width of each and finally add the two answers together.

  • Round pools – multiply the diameter by the diameter to get square of the diameter and then multiply the answers by pi (3.14)

  • Oval pools – multiply the longest diameter by the shortest diameter for surface area.

  • Kidney shaped pools- at the longest and shortest width, and multiply this by the length.

How Big of a Pool Heater Do I Need?

For All Pool shapes –

Find average depth by adding the deepest part of the pool to the shallowest and dividing by 2. Multiply average depth by surface area, it will give you the approximate pool volume in cubic feet. Multiply the number by 7.48 to convert into gallons. volume in cubic feet. Multiply the number by 7.48 to convert into gallons.

2. Your Needs and Preferences

There are two ways to run a pool heater. You can choose to heat from the cold or maintain a constant warm temperature.

pool heat pump size calculator

Every person has to heat from cold at some point, using the heater on a need to heat basis to tackle chilly days is a real option but it requires a more powerful heater to heat. Keeping the pool at a warm temperature day in and day out needs a small heater.

3. Know Your BTUs

Pool heaters measure their power in British thermal unit ( BTU) .

How many BTU heaters do I need?

One BTU raises the temperature of one pound of water by 1 degree fahrenheit. 8.33 pounds of water are there per gallon.

If you have a swimming pool that holds 20000 gallons, then 166000 BTUs are needed to increase by 1 Degree.

Divide the number by 24 to find out how many BTUs are needed to raise the temperature by 1 Degree over 24hours.166000÷24=6916.66.

If you want to increase the temperature of the pool to 80 degrees then you have to subtract your current pool temperature from the desired pool temperature.

How many BTU heaters do I need?

Multiply BTUs per hour to raise the temperature by 1 Degree by the number of degrees that you want. 6916.66 × 20 = 138,333. This is the BTUs you need per hour to raise the temperature by 20 degrees over 24 hours.

For fast heating, you have to increase the amount of BTUs . It is a good idea to overestimate the heating needs by 20% for environmental factors and natural heat loss caused by evaporation.

Pool Heater Sizing Calculator -

The maths involved –

(Difference in desired and air temperature) 20 × 300 (surface area of the pool) = 6000.

6000 × 10 (no. of BTUs per hour per square foot) = 60,000 BTUs per hour. To heat the pool by 20 degrees in just 12 hours multiply the number of BTUs per hour by two. 60000×2=120,000 BTUs per hour. So to heat your pool by 20 degrees in 12 hours you need a heater with capacity of 120, 000 BTUs per hour.

Easier Way – Pool supplies Canada has a chart with some of the most common pool sizes, and estimated BTU requirements. The in-store pool supply retailers will do the maths for you and will suggest the best heater to meet your requirements and clarify your doubt – what size water heater do I need?

4. Use a Solar Cover

Using a solar cover along with the pool heater reduces the amount of energy and time your heater needs to warm the pool and keep the water warmer longer. Solar cover in conjunction with the heater reduces the amount of BTUs required to heat or maintain the pool temperature by 50% to 80%.

pool heater calculation

5. Environmental Considerations

Most of the pool heaters are environment-friendly. Modern propane and gas heaters are more efficient than previous models and far more efficient than oil furnaces, heat pumps are more environmentally friendly than propane and gas, and solar heaters are the cheapest to operate and most environment friendly option but they are the least powerful.

pool heat pump sizing

So you have to make a choice between power and efficiency. If you choose power then you get a few less weeks of pool-time per year, but you can pair a solar heater with a gas heater and switch between the two, to find the right balance of comfort while minimising your energy bill.

What Size of Heater Do I Need for My Pool?

Calculating BTUs depends on completely stable temperature plus you have to consider natural heat loss through evaporation.Natural gas and propane heaters are most powerful followed by electric heaters or heat pumps, less powerful and require temperatures in excess of about 50 degrees to operate.Solar heaters, the most environmentally friendly option but lack raw heating power of gas, propane or electrical units.

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