10 Best In Ground Pool Heaters 2026 in the United States

The Hayward W3H400FDN is a natural gas heater designed for in-ground pools and spas, offering a strong heating capacity of 400,000 BTUs. This makes it suitable for larger pools or those in cooler climates where quick and effective heating is important. One of its standout features is the cupro nickel heat exchanger, which is highly resistant to corrosion, helping the unit last longer even if water chemistry isn’t perfectly balanced.

It also has an efficient hydraulic design that cuts down on the pump’s run time, potentially saving money on energy bills. The heater meets low NOx emissions standards, making it better for the environment compared to some older models. Installation and maintenance are made easier thanks to front-panel access and a user-friendly control pad, so operation and servicing are straightforward.

On the downside, with a weight of 195 pounds and fairly large dimensions, it’s a heavy and bulky unit that may require professional installation. While energy savings are mentioned, natural gas heaters generally have higher ongoing fuel costs compared to some electric options. This heater is a solid choice for pool owners who want strong, reliable heating for large or in-ground pools and value durability and ease of use, but should be prepared for higher installation effort and fuel expenses.

The Aquastrong 75,000 BTU pool heat pump is a powerful choice for both above-ground and inground pools up to 21,000 gallons, making it suitable for larger pools or colder climates where quick heating is needed. It offers a dual-mode system that can heat or cool your pool water, allowing you to swim comfortably almost all year round. One of its standout features is the inverter technology, which adapts energy use dynamically, making it highly efficient—with up to 70% energy savings compared to traditional electric heaters and better efficiency than gas options. This means it can keep your pool warm without drastically increasing your energy bills. It also runs quietly, producing about 53 decibels, roughly the noise of a normal conversation, and includes an automatic defrost function to keep working well in winter. Installation is relatively easy thanks to multiple connection adapters, fitting most pool plumbing setups.

The unit is fairly heavy at 218 pounds, which might require professional help for moving and installation. The upfront cost and the need for a 220V power supply could be factors to consider if your setup isn't already compatible. Its WiFi capability and app control add convenience, letting you adjust settings remotely and monitor energy use. For those looking to extend their swim season efficiently and quietly, this heater provides a reliable solution, especially if you have a mid to large-sized pool and a climate that benefits from both heating and cooling.

The Aquastrong Inverter Swimming Pool Heat Pump is a strong choice for both above ground and inground pools up to 16,000 gallons, thanks to its 55,000 BTU heating capacity. This means it can warm large pools fairly quickly, even in cooler climates. Its dual ability to both heat and cool water allows you to set comfortable temperatures from 47°F up to 104°F, which can extend your swimming season well into spring and autumn. The inverter technology helps keep energy use low by adjusting power in real-time, promising up to 70% savings compared to traditional electric heaters and better efficiency than gas heaters, making running costs more affordable over time.

The unit operates quietly at about 50 decibels, so it won't be disruptive, and the automatic defrost feature ensures it can keep working without interruption during winter. Installation is designed to be straightforward with multiple connection options to fit most pool setups, though being a 220V system, it may require professional electrical work depending on your home. The heater also offers smart features like WiFi control and scheduling through an app, which adds convenience but might be more than some users need.

The pump is solidly built with cast iron and comes with a 3-year warranty, providing good reliability. It is fairly heavy at nearly 150 pounds, so moving or installing it will need some effort. While it is energy efficient, the initial cost and installation might be higher than simpler gas or electric heaters. For those seeking precise temperature control and energy savings for a large pool and willing to invest upfront, this model is worth considering.