After you decide that you want a heater for your pool, you need to decide what type of heater. The main types are gas, solar and electric (primarily heat pumps), but even within these categories there are a number of choices to be made.
Gas pool heaters
This is the most common type and has the advantage of providing heat faster than other options because it is more powerful. In-ground pool heaters can provide up to about 400,000 BTUs. This is especially useful if you heat the pool intermittently and therefore need to raise the temperature quickly.
Gas pool heaters can run on natural gas or propane. Obviously, you'll use natural gas if it's available, and propane will work if you're already storing it for other purposes. If you don't have a gas source already available, a gas pool heater may not be the best option.
Gas pool heaters also come in electronic or millivolt versions. The electronic models are microprocessor controlled with electronic spark ignition, like a modern boiler. Millivolt versions have a pilot light that burns continuously and wastes a small amount of gas. The heat from the pilot light is used to generate a small amount of electricity (about 500 millivolts - hence the name) that powers the controls. The first option is the best, but it requires a power supply. If this is not possible, a Millivolt heater is appropriate.
The disadvantage of gas heaters, especially propane ones, is that they can be expensive to operate.
Electric Pool Heaters
It is possible to purchase an electric pool heaters in Canada, but it is only suitable for small above ground pools.
The type of electric heater that is becoming more common is the heat pump. Heat pumps work by transferring heat from the ambient air into the pool water, rather than by generating heat themselves. This means that in terms of the energy used to heat the water, they can be several hundred percent more efficient. This makes them cheaper to run than gas heaters and more environmentally friendly. They are also expected to have a longer service life than gas heaters.
Of course, heat pumps have their drawbacks. They are not as powerful as gas heaters and must run continuously to maintain the temperature of the pool. They also require a minimum air temperature of 45 degrees to operate effectively.
Solar pool heaters
They work by pumping water through solar panels that are designed to collect solar energy. Typically, the area of solar panels required is equal to the area of the pool. Solar systems may be more expensive to install than gas heaters or heat pumps, but they should last longer and will be less expensive to operate. In addition, it is the most environmentally friendly way to heat your pool.
The disadvantages are that there are many more issues to consider and address with a solar system than with other types of heating, including the solar resource, climate, local building code requirements and safety issues. In particular, you are dependent on the weather and you need to be sure that your pool will be usable for the period of time you want it to.