Pool Heaters Overview

swimming pool heaterLiving in the Phoenix Metro area- where it is not unusual to see temperatures well over 110 for many days of the year- swimming pool heaters might seem like a rarity. Actually, there are many pools in Arizona that do have a heater. This is because many are pool / spa combinations and they all contain a heater.

After all, what good is a spa if you can’t get it nice and hot?

How Long Will It Take To Heat My Arizona Pool Or Spa?

This is a question we get asked a lot.
Gas pool heaters can be designed to run on natural gas or propane. Both types will work the same way and produce the same amount of heat. It is only the fuel source which differs. Water will be directed into the heater from the pool plumbing, and run through a heat exchanger. A heat exchanger (pictured below) is a large copper unit, and can be straight or circular depending on the manufacturer.

After the heater goes through its ignition sequence, it will produce a blue flame in the combustion area. As water flows through the copper exchanger, it picks up the heat and the water flows back to pool- generally achieving a 10 degree temperature rise with each pass. Keep in mind that that water then mixes with the rest of the water in the pool (or spa). It will take a while to reach your “set point” that has been adjusted on the heater thermostat.

Heat Exchanger for swimming pool

Hayward H-Series Heat Exchanger Assembly

Heaters come in several different sizes. The larger the BTU output, the more heat the heater produces. This means a shorter duration of time is needed to heat the pool or spa.

With a 400K BTU heater and a typical Arizona 20,000 gallon pool, you can expect a temperature rise of about 2.5 degrees an hour of run-time.

For an average 500-800 gallon spa, it usually heats in 30-45 minutes. Keep in mind also this also depends on how cold the water is to start. In the dead of winter, with 50 degree water, it might take an hour and a half to bring the spa to 104 degrees.
To bring a 60° pool to a comfortable 85°, with that same heater, usually takes approximately 12 hours of run-time. Smaller size heaters of course will take longer.

Do I Need A Large Heater For A Spa?

Oftentimes, when the pool-spa combo was originally built, the builder put a large heater on so that the pool could heat quickly. If you have an older non-working heater, you do not care about heating the pool, and you just want to get the spa hot, you can downsize the heater to a 110K – 250K BTU model.

It will significantly save on the cost of replacement and be more than adequate for spa only use. Sized specifically for the spa, these heaters will still get up to temp very quickly.

How Much Will It Cost to Run?

This is another question we are often asked about pool heaters. Gas is measured in a unit called a therm. There are 100,000 BTU’s in a therm. Therefore a 400K BTU heater will consume four therms an hour. In the winter months, a pool heater in Mesa, AZ costs roughly $.60 a therm. This amount includes the monthly service charge for the first 1200 therms, and $.47 a therm thereafter.

In round numbers, it will cost about $2.50 for every hour the heater is firing. As an example, if it takes 12 hours to get the pool heated, that would cost about $30.

Keep in mind that this cost is just to get it up to the correct temperatre. To maintain the temperature, will require the heater to cycle- so it would depend on how long you wish to heat the body of water. Of course these figures are estimates, and will vary depending on your locale.

What If I Don’t Have Natural Gas?

steam on heated poolEven if you live in an area or development without natural gas, you can still heat your pool or spa!
Propane is always in option for those with no natural gas access. Gas pool heaters are also available to run on propane and a large propane tank can either be buried somewhere on the property if space allows. A smaller sized tank may be used and located near the pool equipment. Propane pool heaters put out the same amount of heat as the equivalent natural gas model will.

Heat Pumps

For those without natural gas or those who don’t mind waiting longer for the pool to warm, a heat pump could be a viable option.

A heat pump requires no gas, and run on electricity. Think of it as an air conditioner, in reverse. Heat pumps extract heat from the ambient air and transfer it to the water through a heat exchanger. Heat pumps do not put out the same output of heat as a gas heater, so they do take longer to heat. An average heat pump can put out about 110,000 BTU per hour. Compared to a large gas heater it would take close to four times as long to achieve the same temperature set point.

While they are not the greatest choice for those wishing to heat a spa quickly, they may be a great option for someone who has only a swimming pool to heat. It may take longer to heat, but the cost is far less expensive than the gas equivalent. While heat pumps have an initial higher cost when compared to a gas pool heater, a heat pumps can keep a backyard pool at a nice 82 degrees- for around $300 of monthly energy cost.

Heat pumps do have limitations though as the colder the air is outside, the less efficient the heat pump can run and there is a point at below 50 degrees where they really can’t produce much heat. If they are run during the day and a cover kept on the pool, they really can do the job quite well here in the Phoenix area.