Once you have made the decision to buy a pool heater you then have to decide which of the types available you will go for. The choices are between gas heaters, solar heaters, electric heaters and heat pumps but even within these categories there are further options.
Gas Pool Heaters
These are the most common type and they have the advantage of being able to provide heat faster than other options as they are more powerful. Heaters for above ground pools (such as the Pentair Minimax NT) typically supply around 100k BTU, on the other hand a heater designed for an in ground pool (such as the Jandy LXi) can provide up to about 400k BTU. A high powered heater will increase the water temperature quickly and is a good option if you only heat your pool occasionally.
Gas pool heaters are available to use natural gas or propane. Obviously you would use natural gas if it is available and propane would be appropriate if you already store it for other purposes. If there is no existing supply of gas it may be best to look at some other form of pool heater.
Gas heaters are produced in both electronic ignition and millivolt models. Electronic models are micro processor controlled with electronic spark ignition like a modern boiler. Millivolt models use an older technology which uses a permanent pilot light and therefore is slightly less efficient. The heat from the pilot light is used to generate a small amount of electricity (about 500 millivolts – hence the name) which powers the controls. The former is the preferable option but it requires an electricity supply, if this is not possible a Millivolt heater is appropriate.
The major negative with gas heaters, especially those using LPG, is that they can be costly to operate.
Electric Pool Heaters
You can buy direct electric heaters but these are low powered compared to other types and are only really appropriate for use with small above-ground pools.
These days the electric heat pump is becoming and increasing popular choice (such as the Jandy Heat Pump). Heat pumps do not produce heat themselves rather they take heat from the surrounding air and transfer this to the water. This means that in terms of energy used to heat output they can be several hundred per cent efficient. As a result they are cheaper to run than gas heaters and are more environmentally friendly. They are also expected to have a longer lifetime than gas heaters.
Heat pumps do have some disadvantages. They do not have the power of a gas heater and are slow to heat a pool, they work best when used to maintain a constant temperature. In addition the air temperature should be at least forty-five degrees if they are to work efficiently.
Solar Pool Heaters
In these systems the pool water is pumped through solar collectors which are designed to trap solar energy. Although each location is different, a good rule of thumb is that the area of solar collectors should be the same as the pool area. Solar heating will probably be more expensive to purchase and install than other types but should have a longer lifetime and be less costly to operate. In addition it is the most environmentally friendly way of heating your pool.
There are more things that you need to address with a solar system if it is to work satisfactorily. These include the local climate, finding the best location, needing local building codes and making sure the system is safe. In particular you are dependent of the weather so you need to be sure that your pool will be useable for the period you require.