Pool Heating Basics

In the UK, outdoor pools need to be heated in order to make then usable.  Indoor pools also need to be heated in order to make them usable all year round.

The most common temperature to heat pools to is 85°F (29.5°C).  In order to achieve this temperature and maintain it you need to add heat.  The amount of heat you need to add and the method of producing that heat is the subject of much debate and misinformed opinions.  If you have the time to trawl the internet you will find umpteen suppliers of pool heaters who are promoting their favourite heater and claiming that you need model x in order to heat a pool of a certain size and model y if the pool is 10 gallons larger.  Within this site we will aim to cut through all the marketing hype and provide you with a simple guide.  We will happily discuss this with you over the phone or in person.

Let’s look at the basics first.  In order to raise the temperature of a body of water, you need to add heat.  The amount of heat you need to add is simple to calculate if we ignore the loss of heat from the pool.  The complication to this calculation is that as soon as you start to heat the water, heat is lost through the side walls and floor of the pool and more significantly from the surface.   In order to heat the pool you therefore need to add at least the equivalent amount of heat to match these losses plus a margin of additional heat in order to raise the temperature.

Traditionally, gas and oil heaters are sized so as to heat the pool initially at the start of the season in around 2 days of continuous running.  It is therefore easy with this much capacity for the heater to maintain the target temperature during the season with only a few hours a day running.  As air source heat pumps have increased in popularity over the last few years, the methods of calculating the heat pump size has become more critical as these output a lot less heat the gas or oil heaters.  To give a direct comparison, air source heat pumps typically take 10-14 days to heat the pool up at the start of the season and then have to run for 24hrs a day to maintain the temperature.

To make the selection of pool heaters easier, we have put together a table of recommended heaters based on the pool size.  The table can be viewed here – Pool Heater Sizing Table