Solar pool heaters: What you need to know

A swimming pool is a great way to relax, cool off, or get some exercise in warm weather. But what about when the weather starts to get just a little bit chilly? The cost of running a pool heater could have you dreading your monthly energy bill or closing the pool early for the year.

If you’re looking for a more energy efficient way to heat your pool while knocking down your monthly operating cost, solar pool heating could be a good solution.

There are two main ways to heat up your pool with solar power: with a thermal solar collector, or with a heat pump connected to solar panels. Here are their relative merits, and the potential cost savings they offer.

Solar pool heaters work by pumping water from your pool through solar collectors, sometimes called thermal solar panels. While a typical photovoltaic solar panel converts sunlight into electricity, a thermal solar panel collects heat from the sun. A solar pool heater pumps pool water through a length of tubes mounted to thermal solar panels, and the water absorbs heat as it passes through. If you’ve ever felt warm water gushing out of your garden hose on a sunny day, it’s the same principle.

A properly sized and installed solar pool heater can warm up your pool by 10 to 12 degrees F. For many people in many parts of the country, that’ll be enough of a boost to enjoy a more comfortable pool or even extend the swimming season by a month or two.

If you’re considering a solar pool heater, first determine whether you have a large enough sunny site near your pool to mount the collector panels. A general rule of thumb is that the square footage of your collector panels should be equal to 50-100% of your pool surface area. Like photovoltaic solar panels, solar collector panels can be ground or roof-mounted and work best when tilted at a moderate angle and facing south, but they can still be effective on a variety of roof pitches and east-west orientations so long as they are not shaded too much by trees or nearby structures. Your solar contractor and installer can help you find the right setup.

The big advantage of a solar pool heater is the miniscule operating cost compared to a gas heater or an electric heat pump powered by grid electricity. The sun gives you the heat for free, so you’re only paying for the electricity to run the water pump.

Annual cost to heat 1,000 sq. ft. uncovered pool to 80 F

Source: Cost estimates for gas heaters and heat pumps from the Department of Energy. Additional cost for temperature control valve and pump run time estimated at $1/day based on manufacturer and installer observations.

Another upside to solar pool heaters is how long they last. Top brands like Heliocol and FAFCO are sold with 12-year warranties and generally require little maintenance, further reducing the cost of owning a solar pool heater compared to traditional gas or electric heaters. That’s a pretty good deal considering the Department of Energy estimates that solar pool heaters begin to pay for themselves in as little as one year through energy savings.

Solar pool heaters won’t work for everyone, though. If your property has too much shade, you’re out of luck.

The cost of installation also tends to be higher than the alternatives: Most homeowners can expect to pay between $2,500 and $6,500 for their solar pool heater according to one website. Your price will depend on local installation costs, the size of the system, the efficiency of the collector panels, and whether or not you’ll need to upgrade your existing pool pump.

Finally, solar pool heaters put you at the mercy of the weather. If it’s been cloudy for a few days or if you like an early morning dip, expect a cooler pool.

If your summer forecasts tend to be more variable and you want to be sure your pool is at a consistent comfy temperature, there still may be a climate-friendly and cost-saving option for you: an electric heat pump powered by standard photovoltaic solar panels. Pool heat pumps can work without solar panels, but the benefits are bigger when they’re combined.

Heat pumps are an energy-efficient way to heat a pool because they work by transferring ambient heat in the air into your pool water. Even if you pay retail rates for grid electricity, it will often save you money on your energy bills and reduce your carbon emissions, too.

With heat pumps, you can enjoy a reliably warm pool anytime the air temperature is above 50 degrees. You’re likely to pay a bit more for a heat pump vs. a gas heater: One website claims it’s $2,000-$6,000 to install a new heat pump vs. $1,500-$4,500 for a gas unit, though the real-world costs could be higher. A heat pump also takes a bit longer to fully heat a cold pool compared to a gas heater. But you’ll save upwards of $400 per year on your pool heating bill.

Photovoltaic solar panels can help you squeeze even more value out of a heat pump pool heater. Typically, you wouldn’t install a separate solar system for your pool; you’d get solar for your entire house, with enough capacity to power the pool heater along with all of your other appliances and gadgets and electric vehicles.

A larger residential solar installation would cost more up front but offer greater energy savings and potentially qualify for a 30% tax credit through the Inflation Reduction Act. After all, that same sunny roof real estate where you could mount your solar collectors just for heating your pool water would also be the prime location for photovoltaic solar panels that could power your home year-round.

Some installers and solar designers have started to recommend electric heat pumps powered by photovoltaic solar panels over solar collectors and gas heaters because you can enjoy consistent pool (and spa) heating while still effectively netting out your energy costs with a properly sized solar system. Your solar panels will generate electricity on days when you’re not heating your pool, which can offset the energy required to heat your pool on a cloudy day.

The drawback to this system is that you’ll face higher up-front costs to install the solar panels you’ll need to power the pool heater. A standard 100,000 Btu heat pump uses about 5 kilowatts per hour, and the size and cost of your solar system will depend on how often you heat your pool, your climate, and the sun exposure of your roof.

Solar energy is capable of much more than just heating your pool during the summer—you can harness the sun's rays to heat your entire home! The best place to compare options for home solar installations is the EnergySage Marketplace. By registering your property to get solar quotes, you can compare offers side by side from qualified, pre-vetted installers near you and speak with an Energy Advisor to discuss which offer is the best for you. If you're interested in also exploring your solar pool heating options, simply make a note in your account—many PV installers also install solar pool heaters (or can recommend a reputable company to do so).