Gas Swimming Pool Heaters

A swimming pool provides healthy, backyard entertainment for your family and friends. These aquatic playgrounds get the most use during the spring and summer months, but many owners want the option of enjoying their pool & spa as much as possible throughout the year, including in cool weather.

Fortunately, today’s gas pool heaters make it easier and more affordable to keep the fun going longer each year. Modern heating systems are more powerful, efficient, and economical than ever. In fact, when coupled with a pool cover, in some regions, a heater can make it viable to swim virtually year-round.

If your pool does not already have a heater, or if you are on the market to replace an old unit, be sure to ask the right questions to ensure you buy the right one for your pool. Then, you can keep on swimming and enjoying your pool, even on fall or winter days.

When shopping for a pool gas heater, here are some key considerations that should be on your hit list:

1. How energy-efficient is the heater? 

Hands down, energy efficiency is the single most important consideration when purchasing a gas heater for your pool. Doing so will mean achieving the lowest possible operating cost.

To compare models, look at each unit’s official thermal efficiency rating. This standardized rating is determined by certified testing, and it indicates the rate at which heat gets output in relationship to the fuel provided to it; in other words, it measures how efficient is the heater in using gas to generate a unit of heat.

The takeaway message here is this: Invest in a gas heater that has a thermal efficiency rating of 82 to 84 percent. A high number will ensure that the fuel your heater uses to warm your pool is maximized, meaning your model will be easy on both your wallet and on Mother Nature.

2. What size unit will heat your pool at a reasonable amount of time? 

Like many home- and backyard-related heating systems, the power of a residential pool gas heater is measured in a standard unit known as a BTU (British thermal unit). On pool heaters, BTU’s range from 150,000 to 400,000.

The total number of BTUs is critical, as it will determine how long the unit will take to heat a pool. For example, on a 20,000-gallon pool (a common size around much of the U.S.) with no spa, the heater size should be between 250,000 and 400,000 BTUs.

Keep in mind: Any size heater will get the job done—eventually. The real question for you and your family is how long are you willing to wait before can dive in? The relationship between time to heat and model size is key. Selecting an appropriate size is critical.

Various factors determine what size makes sense to suit your preferences and your pool’s needs. Pool size—measured in gallons—is a required factor in determining the heater size heater, and it should be the first one to answer. The reason is simple: The bigger the pool, the more water there is to heat.

Additional factors influence the BTU power needed. They include local climate; wind conditions in your yard; if your pool has a spa; how long you will use your pool throughout the year; if the pool has a cover—and what kind, and how consistently is it used; and how fast you want to be able to heat your pool (and spa).

Do note: The heater size makes all the difference in how rapidly it boosts water temperature. However, once the mercury hits the target, the size makes no appreciable difference in maintaining the temperature.

3. Does your pool have a spa that you want to heat? 

When determining the best size for a pool heater, a spa changes the entire equation. For pools with spas, the most popular size is 400,000 BTUs. And there is good reason why.

Let’s consider a typical scenario for heating a common size spa—700 gallons. (This example would change based on condition listed in #2 above). To raise the temperature from 70 to 100 degrees Fahrenheit, a 250,000-BTU heater can do it in 51 minutes, whereas a 400,000-BTU unit could in 32 minutes.

Now, if you think those 19 minutes are no big deal, make sure you imagine coming home from a rough day at work wanting to immediately plunge your aching back into a hot, bubbling spa; now, picture yourself waiting nearly an hour to do so. This is why overwhelmingly, most pool owners with spas opt for a 400 BTU unit.

4. Will you install the gas heater yourself? 

First off, let’s be clear: Installing a gas heater of any kind requires real technical ability. Only a more advanced DYI-type individual should attempt it.If that describes you (or a willing friend or family member), and you want to tackle the job, be sure to choose a model that’s easy to install.

Your backyard most likely has a gas line in place for your existing heater, and you will need to plumb the new unit to this line. Your best bet will be a model with CPVC inlet and outlet union connections that line up as closely as possible with your current heater connections.

An extra word of caution: With some manufacturers, using anyone other than a licensed installer may limit your heater warranty to parts only, vs. parts and labor.

5. What kind of metal is the unit’s heater exchanger made of?

You want your new heating investment to last. That’s why you want a system with parts and materials that will go the mile and hold up to your pool’s operating conditions.

Toward this goal, the most critical component to seek a heat exchanger made with the optimal material. Many pool heaters use copper for this principal part, which is also the most costly part to replace. However, when it comes to endurance, there is a better option: Cupro-nickel, which kicks plain copper to the curb.

This metal alloy is highly resistant to corrosion, and it offers greater durability and longevity over copper. Even in high-flow pools (such as pools with larger pumps) or those with aggressive water chemistry, Cupro-nickel simply holds up better. For this reason, using heaters with Cupro-nickel components on saltwater pools—which are tough on many metal equipment parts—is also a smart move.

Note: After a heater’s thermal efficiency rating, a Cupro-nickel heat exchanger is the most critical consideration when selecting a heater!

6. What is the heater’s cost up front, and how important to you are operating costs? 

Your goal should not be finding the best deal on a new heater; but finding the best value for your needs. Like most any electronic devices or appliance, an energy-efficient gas heater will cost less to operate. Value comes from lower monthly gas bills that save you money over the life of the heater.

When considering the upfront cost of the unit, reviewing the thermal energy-efficiency rating described in #1 above is imperative. No other factor will so directly impact what you spend on utility costs over time! Think of this efficiency rating as “how much bang for your buck” that the heater will deliver. If you plan to use your heater frequently, investing more up front for an ultra-efficient model can pay off even more.

Tip: In some areas of the country, utility companies offer cash rebates for replacing old swimming pool heaters with high-efficiency units. Check with to your local power company to see if a program exists in your area so you can save a few dollars on your purchase.

7. What does the heater warranty cover, and how long is it good for? 

With a big purchase like a gas heater for your pool, the warranty matters. Not all are created equal. 

When the installation is performed by a licensed installer, models from major manufacturers carry one-year guarantees. Terms vary, so be sure to review the written details to see if they cover parts only, or, parts and labor.

If you are replacing all of the key equipment on your pool—pump, filter, heater—there are opportunities for three-year parts and labor warranties. Some major manufacturers offer these extended terms on equipment bundles when you buy all three components in a single purchase.

Due to the initial purchase price and the ongoing operation cost, choosing the right gas pool heater is a big decision and one that you will live with for at least several years.

Do do your research to find one that will serve you well. After all, a heater shouldn’t be something you have to think about often—it should simply be there providing you with a warm, fuss-free, swim-ready environment to enjoy.