Choosing the Right Size Heat Pump


If you are a manager of an establishment that has a large pool for client use, you’ll want to ensure that you have the correct size heat pump fitted. Whether you have a pool at your educational establishment, hotel, or sports club, you’ll know that heat pumps for commercial pools need to be a lot bigger than ones fitted at home. This is simply because the swimming pools are bigger, with a lot more water filling them. Commercial heat pumps are also designed to be used a lot more than occasional domestic use, so need to be bigger, sturdier, and more long-standing.

Get the Right Size

People often make the mistake of buying under-sized heats pumps, as they don’t fully consider all the factors of pool usage. You should always take the advice of professional fitter when installing a heat pump for a pool, but otherwise you can know what to expect if you understand the sizing guidelines. Heat pumps are measured and sized according to their heat output, and this is measured in BTUs (British Thermal Units). This means that an undersized pump will have to run for longer in order to reach the optimum heat required in a swimming pool. This is no good if you have little time to waste in getting the pool ready for you customers to take a swim. Here are some guidelines to determine the size you’ll need:

  1. Determine your desired water temperature in °C. For most uses the optimum heat should be between 25-28o But it can vary, depending on weather the pool is outside or inside, and what it will be mostly used for.
  2. Determine the average air temperature of the coldest month during which you plan to use your swimming pool in °C. If you have an indoor pool, this will be easier to regulate.
  3. Subtract the average air temperature from your desired water temperature to calculate the required temperature rise. E.g. Pool temperature = 28oC, Average Air Temperature = 15oC; that means the temperature rise needs to be 13o
  4. Calculate the surface area of your swimming pool in square meters m2:
    • Circular pools: radius x radius x 3.14
    • Kidney-shaped pools: length x width x 0.75
    • Oval-shaped pools: (0.50 x length) x (0.50 width) x 3.14
    • Rectangular pools: length x width
  5. Calculate the required BTU output per hour. This calculated as: surface area x temperature rise x 12. As an example, let’s take an Olympic sized pool, certified for races. The length is 50m, and the width is 25m. It is an indoor pool and we have an ambient room temperature that averages to around 20oC, so we need a temperature rise of 5o Now times that by 12. So: (50 x 25) x (25 – 20) x 12 = 75,000.

The figure of 75,000 BTUs per hour is about right for an Olympic sized pool, so it proves the formula is correct. But if any of this sounds confusing, don’t worry! Any supplier of pool pumps will be able to help you with your specifications. Remember, if you can’t find exactly the right size, it’s always better to get an oversized pump than an undersized one, as it will heat your pool even quicker, and won’t be a drain on resources.