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 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.

The Hayward W3H250FDN Universal H-Series 250,000 BTU Natural Gas Pool and Spa Heater is a strong contender for anyone looking to heat an in-ground pool or spa. With a heating capacity of 250,000 BTUs, it is powerful enough to effectively warm large pools. This unit uses natural gas, making it an efficient option that can save on long-term energy costs. Its durable cupro nickel heat exchanger is designed to withstand corrosive conditions, which is beneficial for pools with unbalanced water chemistry.

The heater's hydraulic design aims to save energy by reducing the run time of the circulation pump, adding to its energy efficiency credentials. Additionally, it meets low NOx emissions standards, making it a more environmentally friendly choice. Installation and maintenance are simplified by its front-panel access and intuitive control pad, which users have found user-friendly. However, some may find the initial cost and weight (165 pounds) to be on the heavier and more expensive side. The product dimensions indicate it requires a fair amount of space for installation.

It’s ranked #6 in Swimming Pool Heaters, indicating it’s a popular and well-regarded choice in this category.