GAS HEATER :
A gas heater is the traditional way to heat a spa. Most of the old school pool guys will send you in that direction. It is easy and they don't have to pay your gas bill at the end of the month.
The BTU output of this machines is usually higher because it doesn't cost that much more to make a 200,000 BTU heater than a 400,000 BTU heater. Also they are larger because the lower efficiency ones lose a lot of heat up the exhaust. They could be either natural gas or (LP) propane. Propane is usually the most expensive alternative for fuel cost. The costs can vary wildly depending on local demand and weather conditions. Electricity and natural gas are more controlled by utilities and the price doesn't fluctuate as much.
Natural gas is more resolvable than propane usually but it is available in limited areas and still can cost much higher than a heat pump. If you want to use this heating alternative we recommend that you select a titanium heat exchanger option that is available on some brands as most standard gas heater heat exchangers are made from copper or stainless steel and are very sensitive to PH imbalances that won't be covered by warranty when they start leaking.
An electric heater is another option to consider to heat up your spa.It has a heating element like one on an electric stove or in your domestic hot water tank at home. They are also called tankless. It is an efficient sounding name, but in reality can cost 6 or 7 times as much as a heat pump to run. This is a very expensive option on par with propane, as it will need a lot of electricity to operate. In some cases it is a good alternative were gas heaters or a swimming pool heat pump is not an option. Never use them on a pool. That bill could be equal to a mortgage payment is your pool is cold. There can be a place for them if the spa is small and not used much. You are only heating up 500 gallons instead of 20,000 gallons that might be in an average pool.
SWIMMING POOL HEAT PUMPS
Swimming Pool heat pumps are the natural evolution for heating your pool. They are Inexpensive to run, have long warranties, a long life expectancy, quiet and powerful without spewing toxic smoke around your pool area. They don't consume or burn a fuel to heat. The way they heat is more like moving existing heat from one place to another with a small amount of electricity to run the compressor and fan. We like that they have a titanium heat exchangers so they can take the harsh pool and spa chemicals well. Most swimming pool heat pumps have a dual thermostat settings, one for the pool and one for the spa. You can save a specific temperature for your pool and another for the spa. Some recognize that you have isolated the spa when closing a valve and immediate start your saved spa temperature setting.
If you have a pool that overflows into the spa then elevating the temperature will not take long as the start up temperature in the spa will be already higher if you had been using the heat pump to heat up your pool.
If you chose a heat & cool model swimming pool heat pump then your heat pump will still operate in lower ambient temperatures where it gets below 50 F or 10C, making it ready to heat up your spa during the cold nights in a the Southwest or a Florida winter or a Canadian or New England early spring or late fall.