10 Best In Ground Pool Heaters 2025 in the United States

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 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 35,000 BTU Inverter Swimming Pool Heat Pump is a solid choice for both above-ground and in-ground pools up to 9,000 gallons, offering reliable heating with a 35,000 BTU capacity. Its inverter technology stands out by providing efficient energy use, delivering a high Coefficient of Performance (COP) of 15.8. This means it saves up to 70% energy compared to traditional electric heaters and even outperforms many gas heaters in efficiency, which can reduce your pool heating bills significantly.

One notable feature is its dual-mode system, allowing both heating (from 47 to 104℉) and cooling (47 to 83℉), which helps extend your swimming season by keeping water comfortable in various climates. The unit operates quietly at around 48 decibels, which is about the noise level of a quiet conversation, and includes an automatic defrost function to maintain performance during cold weather.

Installation is designed to be user-friendly, with multiple adapter options to fit most pool plumbing setups, though the unit is fairly heavy at nearly 117 pounds and made from cast iron, so some assistance might be needed during setup. The WiFi-capable timer and app control add convenience by letting you adjust settings remotely and schedule heating, a big plus for tech-savvy users or those wanting precise temperature control.

This heat pump runs on 120V electrical power, which is common but might require an appropriate circuit setup if your pool’s wiring isn’t compatible. Also, the maximum flow rate of 20 gallons per minute should be matched with your pool pump for optimal performance.

If you are looking for an energy-efficient, quiet, and flexible heat pump to keep your pool comfortable through different seasons, the Aquastrong 35,000 BTU model is a compelling option, especially for medium-sized pools. Its modern features and cost-saving operation balance well with its size and installation weight.