Sizing Your Pool Heater: Key Factors to Consider for Optimal Efficiency


Sizing Your Pool Heater: Key Factors to Consider for Optimal Efficiency

A residential swimming pool in Frisco, TX, with clear blue waters reflecting a suburban home, potentially heated for year-round comfort with a pool heater.

Installing a properly sized pool heater is one of the best ways to extend your swimming season and get the most enjoyment from your backyard pool in Frisco, Allen, McKinney, Prosper, and surrounding areas. With the Texas climate, an undersized heater will struggle to keep your pool warm enough for comfortable swimming, while an oversized unit is inefficient and wastes energy.

To make sure your pool heater is optimized for efficiency and performance, there are several key factors to consider when sizing your unit. In this blog post, we’ll go over the elements that determine the right pool heater size, help you calculate the proper BTU output, and provide tips for choosing the best heater for your pool.

Determine Your Pool Volume

The first step in sizing a pool heater is calculating the volume of water in your pool, measured in gallons. The bigger the pool, the more powerful the heating system it requires.

To determine volume, multiply the average length x width x depth x 7.5 gallons (the number of gallons in a cubic foot of water).

For example, for a rectangular pool measuring 16 ft x 32 ft with an average depth of 5 ft:

  • 16 x 32 x 5 = 2,560 cubic ft. of water
  • 2,560 cu ft x 7.5 gallons/cu ft. = 19,200 gallons

Irregularly shaped pools may need to break calculations down into sections. Calculate the volume of each distinct section separately, then add them together.

Knowing your pool’s gallons helps size the heater to adequately heat the total amount of water to the desired temperature within an acceptable timeframe.

Factor in Your Climate

The climate you live in determines how much heat you’ll need to add to maintain comfortable swimming temps. Colder regions like Frisco, Allen, McKinney and Prosper, require more powerful heaters. Summers are hot and humid, while winters are cool.

Here are average climate factors to consider:

  • Summer air temps: 83°F high/66°F low
  • Humidity: 64% avg
  • Water temps: 78°F high/70°F low
  • Swim season: May to September

These factors mean you’ll need a pool heater during the summer mainly to combat cooler early morning and nighttime temps.

Desired Temperature Rise

Most pools are kept in the 78–82°F range for comfortable swimming. To size your heater, you’ll need to know:

  • Desired pool temperature
  • Lowest expected air temperature during swimming months
  • Average groundwater temperature entering pool

Temperature rise refers to the number of degrees your pool heater must raise the water to reach your desired temp.

For example:

  • Desired pool temp: 80°F
  • Lowest air temp: 65°F
  • Groundwater temp: 70°F

Temperature rise = 80 – 70 = 10°F

Knowing your required temp rise allows properly sizing the heater.

Heating Efficiency

Heating efficiency refers to how much heat is transferred to the pool water vs. lost out the heater exhaust.

  • Gas heaters convert 80-84% of fuel into heat, with the rest lost through exhaust gasses.
  • Electric heaters are nearly 100% efficient as all energy goes directly into heating elements.

Higher efficiency means faster heating and lower operating costs. Consider efficiency when choosing gas vs electric.

Flow Rate and Sizing for Turnover

Flow rate is the gallons per minute (GPM) of water flowing through the heater.

Pool heaters work best when the entire volume of water flows through them at least once every 24 hours. This is called turnover.

To properly size, you’ll need:

  • Pool volume in gallons
  • Desired turnover period (24 hours optimal)
  • Recommended flow rate range for heater


  • Pool volume: 19,200 gal
  • Turnover goal: 24 hours
  • Flow rate range: 30-50 GPM

19,200 gal / 24 hours = 800 GPM turnover rate

Choosing heater flow rate of 40 GPM works for proper turnover. With flow rate and volume, you can ensure your pump and filter are appropriately matched.

BTU Output

BTU stands for British Thermal Unit and measures heat. One BTU raises one pound of water by 1°F.

To heat your pool efficiently, your heater’s BTU output must align with:

  • Pool volume in gallons
  • Desired temp rise
  • Regional climate factors

Here is the standard formula:

BTUs needed = Volume in gallons x temp rise x climate factor


  • 19,200-gallon pool 10°F temperature rise 65°F lowest air temp (climate factor of 1.1)
  • 19,200 x 10 x 1.1 = 211,200 BTUs

Select a pool heater with a 210,000+ BTU rating. This ensures your heater can raise 19,200 gallons the needed 10°F efficiently.

Gas vs. Electric Heaters

The two main types of pool heaters run on gas or electric power. Consider:


  • More cost-effective for heating
  • Higher heat output potential , can heat larger pools and faster
  • Natural gas or propane fuel supply required


  • Heat pump models extract ambient heat and are energy efficient
  • Better for smaller pools or modest heating needs
  • No combustion and venting required

Evaluate costs, efficiency, and maintenance when choosing gas vs electric.

RELATED: Pool Heater Types: Decision Making Guide for the Pool Owner

Top Pool Heater Brands

The leading pool heater manufacturers include:

  • Pentair: Variety of gas, electric, and heat pump model options and budget friendly. Known for reliability.
  • Hayward: Top selling gas heaters with up to 400k BTU output. Also makes heat pumps. Quality construction.
  • Rheem: Offers gas, electric, and hybrid heaters. Plus advanced touchscreen controls. Excellent performance and durability.
  • Sta-Rite: Gas and electric choices available. Max-E-Therm models offer up to 80% energy savings.

Consider warranty length, efficiency ratings, smart controls, and cost when choosing among top brands.

Maintain Efficiency with Regular Care 

To keep your pool heater running efficiently for years:

  • Inspect gas supply lines and connections annually for leaks.
  • Check and replace air filters if clogged.
  • Have a pro check heat exchangers, burners, and pilots every 2-3 years.
  • Keep water chemistry balanced. Scale buildup reduces efficiency.
  • Run heater regularly instead of just occasionally to prevent corrosion.

Get a free estimate to ensure you select the optimally sized pool heater for your backyard pool in Frisco, Allen, McKinney or Prosper. Our team provides efficient heating solutions to extend your swim season.

Properly sized heaters improve performance and save energy costs. With experience installing and maintaining various pool heating systems, we accurately assess your climate, pool size and usage to determine the right fit.

Contact us at +1 469 340 2757 or drop us an email at for your free consultation. Investing in a properly sized pool heater maximizes warmth and efficiency while minimizing energy use.

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