Bringing the Heat:  Pool and Spa Heaters 101

Defying the tease of an early spring

We step outside in the morning and breathe deeply the cool Dallas air.  Only a few hours later, the sun compels us to seek shade, and our thoughts go to a refreshing dip in the pool.  Except the pool water is barely 70 degrees and far from relaxing. The early spring tease strikes again.

Heaters allow pool and spa owners to enjoy their investment outside the normal, summer season.  This may seem merely to be a luxury item, but warm swimming waters can serve multiple purposes.  For those of us seeking to rehabilitate from a medical procedure, a daily swim provides a means to exercise with as little physical strain as possible.  Others just need a way for their children to cope with short-timers disease, as summer draws near but not near enough.  Whether you wish to extend the swim season by a month or two or to seize the day and use your pool on demand, a pool/spa heater can enrich your swimming experience.

Break it down

Here are some things to consider before deciding on installation or replacement options:

  • Heat pumps are meant to heat the water very slowly and only by a matter of a few degrees.  They can take the biting chill out of pool water during mild months, or when your pool is under a canopy of trees that block out the summer heat.  They are NOT able to heat the pool on demand, nor will they satisfy the desire for 90+ degree swimming water.  Also, in most cases, they require new electrical service to the pool equipment area (a 60AMP or larger dedicated circuit) and have a substantially larger footprint than other heaters, requiring more space.  These are normally installed at the time of pool installation or during major renovation projects.
  • Small electric heaters are designed for small bodies of water such as spas or very small play pools, those typically covered when not in use.  Their efficiency depends mostly on water volume.  These are used mainly where the spa will be heated nearly year-round, but they are prone to failure.  Manufacturers of such heaters typically reduce the warranty period significantly.  However, when used in the proper application, they can be an energy-efficient solution.  Like heat pumps, they do require a dedicated electrical circuit that is often not available on standard pool/spa equipment pads.
  • Gas-fired heaters are the standard in the pool/spa industry.  Natural gas is the predominant fuel for these heaters, although propane heaters are common for regions that do not have a readily-available natural gas supply.  These are used for heating spa water on demand and for heating pools of any size, even for long-term use.  The manufacturer of each brand of heater specifies certain requirements for these, such as gas pipe sizing, clearances from windows and doors, and minimum water flow needs.  Gas-fired heaters are quite efficient, but how quickly and efficiently they heat the water depends on a couple of factors.  First and foremost is the square footage (area) of the surface of the water.  The larger the surface area, the more evaporative loss occurs.  High winds increase loss to evaporation and slow the heating process.  Ambient air temperature, sunlight, and the volume of the pool also dictate how quickly temperatures will rise.  FYI, these factors for rate of temperature rise apply to all pool/spa heaters.

The match game

Given gas-fired heaters are the most common types of pool/spa heaters, let’s focus on how they relate to your specific needs.  The sizes of these heaters range from 100,000 British Thermal Units (BTU) up to 399,000 BTU, the largest available for residential pools (anything larger becomes a boiler and is heavily regulated).  Assuming your gas pipe size is adequate or can be modified to be adequate, the following are recommendations for which size fits which desired use.

  • If you wish to heat your standard-sized spa quickly (600 gallons or larger) but cannot imagine heating your pool, we recommend nothing smaller than a 250,000 BTU heater.  If it takes longer than an hour to get it therapeutically hot, then it doesn’t really heat “on demand”.
  • If you would like to heat your pool as quickly as possible (i.e., when company is coming on short notice), you should get as large a heater as possible, typically a 399,000 BTU version.  This is also true for those who want to heat their pool for extended periods of time and who own a pool with a deep end.  In these scenarios, the larger heaters are less expensive to run.
  • Smaller heaters can work quite efficiently for those who have smaller pools and want to heat their pools consistently for extended periods of time.  Also, for those who have very small spas (600 gallons or smaller), a 200,000 BTU heater can serve for on demand as well as consistent heating.

The bottom line

So, what to do with this information overload??  First, consider your primary reason for wanting a heater and how often you might use it.  Then, call us today for an appointment.  Our highly-trained technicians have experience and training in analyzing every aspect of your pool, spa, and equipment.  If you have a heater that seems to be in fine shape but needs a tune-up, we can diagnose your problem(s) and recommend solutions to get you enjoying your pool or spa as quickly as possible.

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