The leading source of swimming pool heating for decades has been gas heaters, primarily due to low gas prices. However, with new technology, higher gas prices, and greater long-term efficiency with other methods, consumers have started looking at other, more affordable options for heating a pool.

A gas heater will be your best choice in certain situations. With the many methods available for heating your swimming pool, remember that different methods are better for different environments and swimming pools. When considering options, it’s not just about the features of the heater.

In this article, we’ll be looking at gas swimming pool heaters. There are two types of gas swimming pool heaters: propane pool heaters or natural gas pool heaters. You will need to have either a natural gas hook-up or a propane tank to operate these heaters. Since many homes are already hooked into natural gas, the installation will be easier and less expensive.

If you don’t have natural gas at your house, you will need a propane tank and will need to have it filled periodically. Depending on prices, propane gas can cost two and a half times more than natural gas.

Like gas-powered appliances such as a water heater, a gas water heater for pools has a combustion chamber that heats copper coils. When the pool water runs through those coils, it’s heated as it makes its return to the pool. Then the air transfers to water circulating through the exchanger.

Due to its design, a gas swimming pool heater heats water faster than any other method; on average, depending on the size of the heater, it can increase the temperature 2-5 degrees per hour. This makes these types of heaters an excellent option for pools used for a short time or sporadic use.

Unlike electric heat pumps, gas heaters are not affected by the air temperature, and unlike solar heaters, can operate on cloudy and rainy days, and even in freezing temperatures. However, gas pool heaters are expensive to run, costing anywhere from $200-$500 per month depending on temperatures, and other factors.

Compared to solar heaters with no monthly costs other than maintenance and to the cost of heat pumps in the $50-$150 range per month, gas heaters are much more expensive to operate over long periods.

One thing to keep in mind is that although most heaters are manufactured to operate at up to 2000 feet elevation, they are also available for ranges from 2000-6000 feet and 6000-9000 feet. Another thing to consider is where you live: Texas and California have emission standards, so make sure if you live in these states that you have heaters designed to meet those standards.

If you are looking for more durability, purchase a gas heater with Cupro-nickel heat exchanger and tubing. Cupro-nickel is better than standard copper units for holding up better in salt systems and in fluctuating pH levels. While ASME requires cast iron headers for commercial use, many manufacturers are using polymer/resin headers for better flow and resistance to erosion.

Two other considerations are whether your gas heater will have millivolt or electronic ignition. Millivolt means it has a pilot light that needs to stay lit all the time. Electronic ignition lights with a spark like a gas grill. The latter is more efficient regarding usage and avoids gas leaks due to the pilot light going out.

Hayward H400FDN Universal H-Series 400,000 BTU Pool and Spa Heater,...
  • Standard Cupro nickel heat exchanger for superior value and reliability
  • Patented polymer header and bypass valve design for the ultimate in hydraulic efficiency and reliability
  • Hayward Universal design for easy and versatile professional installation

Sizing a Gas Pool Heater 

There are several factors to consider when sizing a gas pool heater. Start with the surface area of the pool, then look at the difference between the average air temperature and the pool water temperature. You also want to look at humidity levels, night temperatures, and wind speed. If you have higher wind, cool nights, and low humidity, you will want to consider a larger heater.

Smaller heaters are slower to heat and will have to work harder, shifting some of the savings from purchasing it to higher running costs. Keep in mind that the larger the pool heater, the faster it will warm your water, saving on heater running costs.

When in sizing a gas heater is take into consideration whether your pool has a cover, or if you will only rarely use the heater. Installing wind blocks can reduce demands on the pool heater and can also affect the size of the heater you’ll need.

An additional consideration is whether the pool is an above ground pool heater or inground. Above ground can be in the 100K range for gas pool heaters. Above ground using heat pumps would be in the range of 50-75K BTU while inground would be in the 100-150K BTU range.

Sizing a pool heater is easier when you anticipate your usage patterns. If you only heat intermittently, like only on weekends, a quick heat up is necessary. Gas heaters add 1-2 degrees of heat per hour, so a more substantial heater would be better in this case. If you decide to maintain the temperature using a thermostat and only to increase the temperature in the evening, smaller heaters have to run more and are thus slightly less efficient.

Take these steps to get an approximate size of your gas heater:

  1. Decide on your desired pool temperature
  2. Calculate the average temperature for the coldest month you’ll be using the pool
  3. Subtract #2 from #1 to get the temperature rise you need
  4. Determine the pool surface area (in square feet)
  5. Calculate with the following formula: Temperature Rise x Pool Area x 12

As a guideline for sizing, factoring in usage patterns and other efficiency measures, here are some measurements to use for gas pool heaters (then go one more size up to be sure):

Size Sq. Ft. Surface Area Gallons
100-200 BTU up to 300 sq ft 1,000 – 10,000 gals
200-300 BTU up to 500 sq ft 10,000-20,000 gals
300-400 BTU up to 800 sq ft 20,000-40,000 gals
400 BTU up to 1200 sq ft. 40,000-80,000 gals

Gas Pool Heater Efficiency

To determine the energy efficiency of a gas pool heater, new heaters go through a standard test to find their BTU (British Thermal Unit) output. Efficiency is the ratio of energy input to usable output: what goes in and what comes out. For example, a heater that is 90% efficient uses $90 worth of heat for every $100 of fuel. The waste is 10%. In today’s market, new heaters are in the 89-95% range of efficiency.

Proper installation and regular maintenance can optimize efficiency. Follow the owner’s manual for recommendations and maintenance schedule; tune up your heater every year.

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Installing and Maintaining a Gas Pool Heater

A gas professional should make the gas connection from the meter, to the heater, and to the gas source. Place the unit on a fire-proof base and allow adequate ventilation.

With care, a gas heater can operate for 10-20 years with timely repairs. However, they can also require more maintenance than other types of heaters.

If your pool is in a cold-weather location, you are in a high electricity cost area, or you want heat fast, adequately sized gas heaters are a good option for use in any climate, year-round.

Pros and Cons of a Gas Pool Heater

One of the main advantages of a gas pool heater is its lower initial investment. Many are available for under $1,500 compared to heat pumps in the $2,000-$4,000 range. A big advantage is that gas heaters heat faster. And unlike heat pumps, gas heaters are not dependent on the air temperature.

On the downside, gas heaters are the least efficient method of heating your pool. Their lifespan is much shorter as well. Although they can last longer with regular maintenance and repairs, their average lifespan is five years. Not only are they more expensive to operate, because they emit carbon dioxide, but they also have a higher environmental footprint.

In comparison, a heat pump pool heater can save up to 40% over natural gas and 75% over propane gas. However, if you are in a northern state using an air-source electric heat pump, if the temperature drops below 50 degrees, the heat pump switches to resistive heating (heating electric coils), and in that case, will cost more to run than either gas.

Raypak 105,000 BTU Swimming Pool and Spa Heater - Natural Gas
  • Designed for easy installation on above ground pools, smaller in-ground pools, and spas
  • Standard 120v 3-prong power cord or can be easily converted to 220v
  • Simple analog thermostat dial for accurate pool and spa temperature setting

Conclusion

For certain circumstances, a gas pool heater is a good option. However, overall, they are beginning to be replaced by other options. While gas pool heaters remain popular, they are best for pools that aren’t used regularly.

One thing to consider is to have two heating systems. For example, you can install a solar system that is highly efficient to maintain a specific temperature over more extended periods, then have a gas system for those times when you want to crank the heat, or if you are in an area not conducive to heat pumps.

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