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    Pool Heater Sizing

    09/ 08/ 2015 0 Comments

    Pool heaters seem to be a hot topic that we get in our stores every year. Some customers come to us and aren't sure whether they should purchase one or not because of stories that they have heard from their neighbours, their friends or even from their own past experiences. We have heard a lot of these stories over the years and have pin pointed the major culprits, the biggest one being pool heater sizing.Pool Heater set up outside.

    First off what I mean by size is how many BTU (British Thermal Unit) the heater has. BTU refers the amount of heat a machine can produce. If we take a BBQ or an oven for example both of these produce heat which could be measured in BTU. Therefore a "bigger" heater simply means that it can produce more heat.


     Before talking about size requirements it would be interesting to understand the process of heating a pool. Your pool is currently at a certain temperature and you wish to increase this temperature. The heater will then heat the water that passes through it introducing heat into the pool. Now if you've ever done the dishes at home you know that if the water that fills the sink is cold and you add a small amount of hot water it stays cold. This means there needs to be a certain amount of hot water added to cold water for the temperature to rise. Now if we come back to the pool, which lets face it is much bigger than a kitchen sink, this process of heating will take a pretty long time. It will take enough time that some of the introduced heat will actually leave the pool. Heat will escape from the top of the pool trying to find equilibrium with the ambient temperature. 

    This is where the size of heater comes into play. The process mentioned above is inevitable but one thing to keep in mind is the heat coming into the pool and the heat leaving the pool are both time based. When an adequate size heater is used for your pool the time required to heat the pool will be much quicker than the heat leaving the pool, which results in you obtaining your desired results.

    Factors influencing size

    Let's look at the specific factors that can make the explanation seen above more concrete. We can split the heating process into two actions making it easier to analyze your needs. The first being heat introduction and the second being heat lost.

    When we are talking about heat introduction the parameter to look at is the volume of water. Knowing the volume of your pool will set the foundation for choosing a heater and will give you a pretty good idea as to which size you will need. If you do not know the volume of your pool, a good way to estimate is to measure the length and the width as well as the depth. Most pool stores will be able to help you with the rest once you know those measurements. 

    Now for step two, heat loss. Heat loss is something that most pool stores will not take into consideration when selling a pool heater. We are no exception, before this summer we were not taking this into factor as much as we should have. A commonly known property of heat in air is that it rises, well this doesn't change when it comes to water. Since the top of your pool is exposed most of your heat will be lost this way. To estimate how much heat you will lose we factor in the surface area of the water. The bigger the surface area, the more heat can escape from the top. It is also important to note that the exposure to wind will factor into heat loss. The more the pool is exposed to high winds the faster the heat loss occurs. 

    In most cases the volume of water and the exposed surface area are proportional. The only time this assumption is not valid is when the pool is deeper then the norm. Having a deeper pool will increase the volume of water with the surface area being unchanged. 


    In case you got lost in all of this or simply want a small check list, here are the essentials:

    • Know the volume of water your pool contains.
    • Know the surface area of your pool.
    • Is your pool exposed to a lot of wind?

    For those of you who want a more concrete idea you can use this chart. If you find yourself sitting on the fence where one heater is barely enough and the other is more than necessary, I would recommend investing in the bigger heater. This will help greatly with the maintenance and in the long run you will save on some repair bills. Since were in the subject of saving, using a solar blanket is highly recommended when buying a heater to preserve heat loss at night. Here's why.