How Pool Heating Costs Are Estimated

The calculator above gives you a realistic projection based on several factors that matter in the real world. It does not just assume you heat the pool from cold once. It accounts for the fact that you maintain a temperature over weeks and months, and that heat loss happens every night.

The formula for the initial heat-up is straightforward: pool gallons × 8.34 lbs × temperature rise = BTUs needed. The cost then depends on your heater type and energy price. For daily maintenance, we apply a reheat penalty: pools typically lose 5°F overnight without a cover, but only 2°F with a good solar cover. That’s why a cover can cut your monthly bill by more than half.

Pool Heater Types Compared

What About Solar Pool Heating?

Solar heating uses panels on your roof or nearby to capture the sun’s energy and transfer it to the pool water. The ongoing fuel cost is zero because the sun is free. However, the up-front installation cost is higher, and performance depends on how sunny your location is. Solar is not included in this calculator because there is no energy bill to project, but it’s worth considering if you live in a sunny area and want the most sustainable option. Many pool owners combine solar with a small heat pump for cloudy days.

How to Lower Your Pool Heating Bill

1. Use a solar cover every night. This is the single most effective step. It stops evaporation, which is the main source of heat loss.
2. Reduce the thermostat by 2 degrees. Going from 84°F to 82°F can save 10-15% on your energy bill.
3. Heat only on days you use the pool. If you swim 3 days a week, there is no need to keep the pool at temperature on off days if you are willing to fire up the heater a few hours before use.
4. Add a windbreak. Shrubs, a fence, or a solid panel block wind that accelerates surface cooling.
5. Service your heater annually. A clean heat exchanger and proper gas pressure improve efficiency.

Understanding BTU Sizing for Pool Heaters

The output of pool heaters is measured in BTUs per hour. As a rough guide, multiply your pool surface area in square feet by 15 to get the minimum BTU/hr needed to maintain temperature, and by 20-25 if you want a fast heat-up time. A typical 400 sq ft pool calls for at least a 200,000 BTU gas heater or a 100,000 BTU heat pump (since heat pumps run longer).

Frequently Asked Questions

How much does it cost to heat a pool per month?

For a 15,000-gallon pool in the Midwest heated to 82°F with a gas heater and used 3 days a week without a cover, expect around $90-$130 per month. With a cover and a heat pump, that can drop to $30-$50. Use the calculator to get your exact projection.

Gas heater vs heat pump: which is cheaper to run?

In most areas, a heat pump costs 50-70% less to operate than a gas heater for the same temperature rise, but it heats more slowly. Over a full swim season, the savings with a heat pump can be substantial, especially if combined with a pool cover.

Does a pool cover really save money?

Absolutely. A solar cover reduces overnight heat loss from around 5°F to about 2°F. That alone cuts your reheat cost by more than half. It also reduces water evaporation and chemical loss.

How can I estimate my unheated pool temperature?

In the summer, an unheated pool in the South typically settles around 78-82°F, while in the North it may be 68-72°F. Check with a thermometer on a typical sunny day before you start heating for the season. Our regional selector sets a reasonable starting point.

What is the ideal swimming pool temperature?

For active swimming, 78-80°F is comfortable. For leisure and family use, 82-84°F is most popular. Therapy pools are often kept at 86-90°F. Every degree above 80°F adds roughly 5-8% to your heating cost.