Pool Heater Size Calculator
Calculate the right BTU heater for your pool. Compare gas, heat pump, and solar heating options with estimated operating costs.
Standard Heater Sizes
Heating Method Comparison
| Feature | Gas Heater | Heat Pump | Solar |
|---|---|---|---|
| Est. Monthly Cost | $1,868 | $325 | $0 |
| Initial Heatup Time | 17 hrs | 44 hrs | 24-72 hrs |
| Upfront Cost | $1,500 - $3,500 | $3,000 - $6,000 | $3,000 - $7,000 |
| Lifespan | 5-10 years | 10-20 years | 15-25 years |
| Best For | Quick heating, cold climates, occasional use | Regular use, mild climates, energy savings | Warm/sunny climates, eco-conscious owners |
| Energy Source | Natural gas / propane | Electricity (COP 5.0) | Sunlight (free) |
* Monthly costs assume maintaining 82°F in 70°F outdoor temp. Gas at $3.50/therm. Electricity at $0.13/kWh. Actual costs vary by location and usage.
How It Works
The heater BTU requirement is calculated based on the amount of energy needed to raise your pool's water temperature, accounting for heat loss from wind and evaporation.
- Water weight is calculated as gallons x 8.34 lbs per gallon.
- Base BTU = water weight x temperature rise (desired minus current).
- Wind exposure increases heat loss by 25% (moderate) or 50% (high).
- A pool cover reduces heat loss by approximately 25%.
- The calculation assumes a 24-hour heatup target at 80% heater efficiency.
Monthly operating costs are estimated based on maintaining the desired temperature against ongoing heat loss.
Frequently Asked Questions
What size pool heater do I need?
Heater size depends on pool volume, desired temperature rise, wind exposure, and whether you use a pool cover. As a general rule, you need about 50,000 BTU per 10,000 gallons of water for a 20-degree temperature rise. This calculator accounts for all these factors to give you an accurate recommendation.
Gas heater vs heat pump: which is better?
Gas heaters heat water faster and work in any temperature, making them ideal for occasional use or cold climates. Heat pumps are 5x more energy-efficient and cost much less to operate, but they work best when air temperature is above 50 degrees F. For regular use, a heat pump typically saves $1,000-$2,000 per year in operating costs.
How long does it take to heat a pool?
A gas heater typically raises pool temperature 1-2 degrees per hour. A heat pump raises it about 0.5-1 degree per hour. For a 20,000 gallon pool going from 60 to 82 degrees F, expect about 12-24 hours with gas or 24-48 hours with a heat pump. Using a pool cover can reduce heating time by 25-50%.
Does a pool cover really save on heating costs?
Yes, a pool cover can reduce heat loss by 50-70%, which directly translates to lower heating costs. Most heat loss occurs through evaporation from the water surface. A solar cover can even add a few degrees of heat during sunny days while preventing heat loss at night.