In 2013, the U.S. Department of Energy handed down a do-or-die policy that shook up the HVAC industry: Gas-fired heaters of all types would have to meet a thermal performance efficiency of 82%.

This requirement, the agency figured, would save approximately 2.81 quadrillion British thermal units over a 30-year period. To put it into perspective, that’s how much energy 15 million American households use in a single year.

Hey, every little bit helps.

Of course, the policy also applied to pool heater manufacturers — only they were well ahead of the DOE’s mandate. Most already had at least one product, or had one in development, that met or exceeded that standard.

Today, manufacturers are still tweaking and refining in pursuit of the most efficient gas heaters. Here, we explore how these appliances are firing up pools and spas more quickly, while conserving more energy than ever before, and what advancements are on the horizon.

Explaining efficiency

When manufacturers tout “high efficiency” gas heaters, they’re talking about how effectively their appliances utilize thermal energy — not electrical energy — to heat a body of water. For example, to say a heater is 82% efficient means only 18% of heat generated will go out of the exhaust.

What has helped some manufacturers achieve greater thermal performance is a technological shift away from a form of combustion that relied on natural air to ignite a flame. Some of these atmospheric-style heaters were prone to problems. A strong gust of wind down a wall or behind the heater could create a downdraft, forcing the flame to roll out of the appliance, damaging components. The advent of fan-assisted, sealed combustion solved this by forcing air into the combustion chamber, delivering a precise mix of air and fuel to create a clean, reliable burn.

“The fan-assisted combustion process is not affected by wind and provides uninterrupted heating performance,” says Bruce Aubrey, heating product manager at Hayward Industries.

This approach can yield a higher thermal efficiency and reduce nitrogen oxide (NOx) emissions. As a result, some brands have rendered their lines of atmospheric heaters obsolete.

That isn’t to say sealed-combustion is the only answer. Raypak managed to retool the old technology to achieve a desirable thermal- and low-NOx quotient in a line of commercial pool heaters that it continues to produce.

“With high efficiency, there are so many routes you can take,” says Terry Doyle, Raypak marketing manager.

The next leap forward

Sealed combustion — neat as it is — is not the technology that’s heating pools with 90%-and-greater efficiency. Eighty-four percent is about all the juice you can squeeze out of this type of heater, which is still pretty good. In fact, units in the low- to mid-80% range account for the vast majority of residential heaters sold today.

Ultra-efficiency, however, is the new benchmark. For years, manufacturers have strived for 100% efficiency. And they’re getting close.

Darn close.

Pentair recently rolled out the ETi 400, which funnels 96% of the BTUs it creates into the pool or spa. But other companies are nipping at its heels. The Jandy Hi-E2 boasts a 95% rating and the Raypak X94 clocks in at 94%.

That leaves as little as 4% of combustion wasted.

The big breakthrough that’s helping them capture more BTUs is called a condensing heater. This technology essentially extracts so much heat from the exhaust that it no longer generates water vapor. (Have you ever put your hand over an old pool heater and felt hot moist air rising out of it? You wouldn’t feel that coming from a condensing unit.) As a result of the cooler exhaust, steam that would otherwise go out of the flue turns into condensate.

Think of it this way: The heat exchanger is working so hard that it’s sweating.

Of course, condensing heaters pose certain maintenance considerations. (See sidebar.)

The rebate debate

All this progress begs the question: Could high-efficiency, gas-fired heaters receive the same incentives that variable-speed pumps currently enjoy?

That’s a big maybe.

Some manufacturers think there are opportunities to explore this possibility for the commercial-side of the pool business, where heaters run every day for longer periods. It would behoove health clubs and hotels to upgrade to save on gas and, thus, experience a quicker return on investment. And municipal utility providers would be wise to incentivize them.

But homeowners? Not so much.

In backyard pools, heaters are used with far less frequency. A survey conducted by the California Energy Commission found that residential pool heaters only cost about $300 a year to run — not enough to justify developing a whole program around.

“I don’t see that forming the basis of a rebate program,” opines Gary Fernstrom, an energy consultant and retired executive with Pacific Gas & Electric.

Where Fernstrom does see potential is in a heater’s hydraulic performance. It takes a lot of energy on the pump’s end to push water through the heater. Anything that would ease strain on the pump could be seen as a rebate contender.

“We’ve been trying to get manufacturers to reduce friction or resistance,” Fernstrom says. “And then you could turn down the speed on a (variable speed) pump” and yield energy savings.

Zodiac is making that argument now, and it goes like this: Most homeowners only use their heater 100 hours a year. Their pool pumps, however, run 3,000 hours a year. So, for 2,900 hours a year, the pump is working harder than it needs to. That’s why the company developed a technology that allows water to essentially bypass the heater when it’s not in use.

“This is where we see utilities becoming far more interested in the heater,” says Jeff Holmquist, product manager at Zodiac Pool Systems.

Pentair, too, sees possible utility perks with its upcoming hybrid heater. This combination unit has both a condensing heater and a heat pump working in tandem. The gas-fired heater will get the pool or spa up to the desired temperature, and then the heat-pump would “maintain the temperature at much lower energy costs,” explains Azur Dzindo, Pentair’s product manager.

Looks like we might reach 100% yet.