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Your pool heater finally gave out. Before you buy a replacement, it's worth taking a few minutes to do your homework. The right unit can save you hundreds of dollars a year in fuel costs. The wrong one will cost more to run and wear out faster. Here's what to know before you buy.
Three Types of Pool Heaters
Pool heaters come in three types: gas, solar, and electric heat pump.
Solar heaters cost less to operate and are a smart long-term investment if you live in a sunny state with rebates available, though they heat more slowly and require a higher upfront cost.
Electric heat pumps are highly efficient and work well in warm climates. They cost more upfront and heat more slowly than gas, but they're a great fit for swimmers who want a heated pool nearly year-round.
Gas heaters are the most common choice nationwide. They heat faster than any other type, work regardless of weather or sunlight, and tend to cost less upfront. If you have an inground spa, gas is almost always the right call.
The rest of this guide focuses on gas heaters since they're what most pool owners are replacing.
How to Size Your Gas Heater
Gas heater size is measured in BTUs (British thermal units). The higher the BTU rating, the faster the heater warms your water.
BTU Guidelines by Pool Size
| Heater Size | Pool Size | Pool Surface Area |
| 100,000 -- 200,000 BTU | 1,000 -- 10,000 gallons | Up to 300 sq. ft. |
| 200,000 -- 300,000 BTU | 10,000 -- 20,000 gallons | Up to 500 sq. ft. |
| 300,000 -- 400,000 BTU | 20,000 -- 40,000 gallons | Up to 800 sq. ft. |
| 400,000+ BTU | 40,000 -- 80,000 gallons | Up to 1,200 sq. ft. |
Note: manufacturers often drop the trailing zeroes, so a "200" unit means 200,000 BTU.
Other Factors That Affect Size
A few things can push you toward a higher BTU rating:
- You heat the pool only for short periods and need fast results
- Your pool gets significant wind exposure
- You live somewhere with cool nights or low humidity
- You want to heat a spa quickly
If you heat your pool for weeks at a time or maintain a steady temperature all season, a lower BTU unit will get the job done for less money.
Not sure what size you need? A pool professional can run a sizing analysis for your specific pool. Getting this right matters: an undersized heater runs longer, burns more fuel, and wears out faster.
Efficiency Ratings and What They Cost You
Efficiency is the single biggest factor in your monthly fuel bill. Today's top gas heaters run at 90 to 95 percent efficiency. If your old unit was rated at 65 or 70 percent, upgrading will pay for itself.
Here's what switching to a 95% efficient heater saves you annually, based on $1,000 in yearly heating costs:
| Current Heater Efficiency | Annual Cost at 95% | Annual Savings |
| 55% | $580 | $420 |
| 60% | $630 | $370 |
| 65% | $685 | $315 |
| 70% | $735 | $265 |
| 75% | $790 | $210 |
| 80% | $840 | $160 |
Source: energy.gov
High-efficiency models cost more upfront, but those savings add up fast.
Features Worth Paying For
When comparing models, look for these features:
Electronic ignition eliminates a pilot light that burns gas around the clock. It's safer and cheaper.
Dual thermostat lets you heat only the spa without raising the whole pool temperature. Essential if you have a pool/spa combo.
Cupro-nickel heat exchanger holds up better in salt water pools and pools with fluctuating pH. Worth the upgrade if either applies to you.
Forced draft system counteracts wind interference so outdoor conditions don't reduce your heater's performance.
Low NOx rating meets the toughest emission standards in the country. Even if your state does not require it, Low NOx heaters are more efficient and cost less to operate.
High-altitude rating is required if you live above 2,000 feet.
Most homes run on natural gas, which is the cheaper and more widely available option. If natural gas is not available at your property, propane works the same way but typically costs more.
Ready to Replace Your Pool Heater?
Blue Haven has installed and replaced pool heaters across the country for decades. If you want help sizing a unit, comparing models, or getting a quote on installation, our team can walk you through it.
