10 Best In Ground Pool Heaters 2025 in the United States

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.

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.