Pool Heating Cost Calculator
Calculate exact monthly pool heating costs for gas, electric, or heat pump systems. See seasonal expenses and compare heating methods.
Heater Type
The type of heater installed on your pool. Gas burns natural gas; electric uses resistance heating; heat pump moves heat from the air.
The length of your pool from wall to wall.
The width of your pool from wall to wall.
The average depth — add the shallow and deep end depths and divide by 2.
The temperature you want your pool water to reach for comfortable swimming.
The typical outdoor air temperature during your swim season. Check your local weather averages.
The thermal efficiency rating of your gas heater — check the label or manual. 0.82 means 82% efficient.
The price you pay per therm of natural gas — check your utility bill.
Use a Pool Cover?
A pool cover dramatically cuts heat loss when the pool is not in use. Select yes if you cover your pool overnight or during non-swim hours.
How many months per year you heat and use your pool.
Your Pool Heating Costs
Estimate includes initial heat-up in month 1, then ongoing maintenance heating for 5 additional months.
💡About this calculator▼
Find out exactly how much it costs to heat your pool each month and across your entire swimming season. This pool heating cost calculator accounts for the energy needed to raise your water temperature plus the ongoing heat loss from your pool surface. Enter your pool dimensions, heater type, local utility costs, and whether you use a cover — the calculator shows your First Month Cost (includes initial heat-up), Ongoing Monthly Heating Cost, and Total Seasonal Heating Cost so you can budget accurately.
Whether you have a gas heater, electric resistance heater, or high-efficiency heat pump, this calculator compares real expenses side-by-side. See how much a pool cover saves you and understand exactly where your heating dollars go.
The calculator finds two things: how much energy you need to heat the pool from its current temperature to your desired temperature, and how much heat escapes every day through the pool surface.
First, it calculates Initial Heat-Up Energy in BTU (the amount of heat needed to raise the water). Then it computes Daily Heat Loss by measuring your pool's surface area and applying the physics of water evaporation and heat radiation — an uncovered outdoor pool loses roughly 12 BTU per hour per square foot for every degree your pool is warmer than the air. A pool cover cuts that loss by about 75%.
The calculator multiplies daily losses by 30 to get Monthly Energy Demand, then converts that to either therms (gas), kilowatt-hours (electric or heat pump), and multiplies by your utility rate and heater efficiency. The result: First Month Cost (heat-up plus losses), Ongoing Monthly Heating Cost (maintenance only), and Total Seasonal Heating Cost across all months you run the heater.
📐How it's calculated▼
The formula has three main steps. Step 1 calculates how much heat energy you need: multiply your pool volume in gallons by 8.34 (the weight of water in pounds per gallon) by the temperature difference you want to achieve. This gives you Initial Heat-Up Energy in BTU. Step 2 calculates ongoing losses: multiply your pool's surface area (length × width) by 12 BTU per hour per square foot per degree of temperature difference, then by 24 hours and 30 days. A pool cover multiplies this by 0.25 instead of 1.0 because it blocks 75% of losses. Step 3 converts BTU to fuel units: divide by 100,000 for gas therms, or by 3,412 for electricity kilowatt-hours. Then multiply by your utility rate and divide by your heater's efficiency.
Example: You have a 20×10 foot pool, 5 feet deep on average. You want 82°F water, the air is 65°F, and you run the heater for 6 months. Pool volume = 20 × 10 × 5 × 7.48 = 7,480 gallons. Temperature rise = 82 − 65 = 17°F. Initial heat-up = 7,480 × 8.34 × 17 = 1,062,323 BTU. Daily loss without cover = (20 × 10) × 12 × 17 × 24 = 97,920 BTU/day. Monthly loss = 97,920 × 30 = 2,937,600 BTU. If you have a gas heater at 82% efficiency costing $1.20/therm, first month therms = 1,062,323 + 2,937,600 = 3,999,923 BTU ÷ 100,000 ÷ 0.82 = 48.8 therms = $58.60. Ongoing months = 35.8 therms/month = $42.96/month. Six-month cost = $58.60 + (5 × $42.96) = $273.40.
📎Source: ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers)
🔍Finding your inputs▼
Pool Length (ft) Measure the distance from one long wall of your pool to the opposite long wall. Use feet, not meters.
Pool Width (ft) Measure the distance from one short wall to the opposite short wall, again in feet.
Average Pool Depth (ft) If your pool has a shallow end and a deep end, add those two depths and divide by 2. Use that number here.
Desired Pool Temperature (°F) Enter the water temperature you find comfortable for swimming. Most people prefer 78–82°F. Higher temperatures cost more to heat.
Average Outdoor Air Temperature (°F) Use the typical outdoor air temperature during your swim season, not the peak summer high. Check your local weather history online — take the average of daytime highs during the months you use your pool.
Heater Type Choose gas (burns natural gas), electric (resistance heating that converts electricity directly to heat), or heat pump (pulls heat from the air). Heat pumps are most efficient but perform worst in very cold climates.
Gas Heater Efficiency Find this on your heater's nameplate or manual. It shows the fraction of fuel energy that becomes pool heat. Typical values are 0.80 to 0.85. Enter as a decimal: 0.82 means 82% efficient.
Electric Heater Efficiency For standard electric resistance heaters, this is always 1.0 (100% efficient) because the electricity converts directly to heat with no losses.
Heat Pump Coefficient of Performance (COP) This number tells you how much heat the pump delivers per unit of electricity used. A COP of 5.0 means 5 units of heat out per 1 unit of electricity in. Check your heat pump's specification sheet. Typical values are 5.0 to 6.0 in moderate climates.
Natural Gas Cost ($/therm) Find this on your natural gas utility bill. It shows the price per therm — one therm equals 100,000 BTU. Look for the rate in the fine print or call your utility.
Electricity Cost ($/kWh) Find this on your electric utility bill. It is the rate per kilowatt-hour. This is different from any fixed monthly fee.
Use a Pool Cover? Select yes if you cover your pool overnight or during non-swimming hours. A cover cuts heat loss by roughly 75%. Select no if the pool stays uncovered year-round.
Swimming Season Length (months) Enter how many months per year you actively heat and use the pool. Six months (May–October) is common in most of North America.
⚠️Special situations▼
Desired temperature is at or below the outdoor air temperature
If your desired pool temperature equals or falls below the average outdoor air temperature, the calculator returns $0 — the sun heats the pool naturally and your heater does not run. Raise your desired temperature or choose a warmer season if you want heating costs.
Pool dimensions result in zero or negative volume
If any dimension (length, width, or depth) is zero or negative, the calculator returns an error because you cannot heat a non-existent pool. Re-enter your actual pool measurements.
Heater efficiency is set to zero
An efficiency of zero causes a division error in the calculator. Check your heater nameplate — efficiency must be between 0.50 and 0.99 for gas heaters, or 1.0 for electric. Re-enter the correct value.
Heat pump in very cold climates (below 50°F ambient air)
Heat pump efficiency (COP) drops sharply when outdoor air is below 50°F. The calculator assumes your stated COP but real performance may be much lower — perhaps 2.0 to 3.0 instead of 5.0 to 6.0. If you live where winter air regularly dips below 50°F and you heat year-round, actual costs will be higher than shown.
Electric resistance heater efficiency entered above 1.0
Electric resistance heaters cannot exceed 100% efficiency (1.0). If you entered a higher value, reduce it to 1.0. You cannot get more heat energy out than you put in as electricity.
Swimming season length is zero or negative months
If you enter zero or negative months, the calculator returns $0 seasonal cost because you do not run the heater. Enter the actual number of months you heat your pool.
Pool cover status is uncertain or used sporadically
A pool cover must be used consistently overnight and during non-swim hours to deliver the 75% loss reduction this calculator applies. If you use it only occasionally, select no and costs will be higher than reality. Invest in regular cover use for real savings.
Initial heat-up cost seems very small compared to monthly maintenance
This is normal. The initial one-time heat-up is small compared to the ongoing daily losses that accumulate month after month. For small pools or small temperature rises, the initial cost is almost invisible. For large pools or large temperature differences, initial cost becomes significant.
❓Common questions▼
Why is my first month cost so much higher than other months?
The first month includes two things: the initial energy to raise your pool water from its current cold temperature to your desired comfortable temperature, plus one month of ongoing heat losses. Once the pool reaches your desired temperature, you only need to replace the heat that escapes through the surface — that is why Ongoing Monthly Heating Cost is lower.
Think of it like filling a bathtub: the first time takes a lot of water, but keeping it full afterward takes just a little water to replace what drains out. The bigger the temperature gap between your starting water and desired temperature, the bigger that first-month jump.
How much money does a pool cover actually save?
A pool cover reduces Daily Heat Loss by about 75% — meaning your Ongoing Monthly Heating Cost drops to roughly one-quarter of what it was without a cover. For example, if a month costs $100 without a cover, it drops to around $25 with a cover.
Multiply that monthly savings by 6 months and you save about $450 per season on a typical pool. The cover itself costs $100–$300 and lasts 3–5 years, so it pays for itself many times over. Savings are largest when there is the biggest temperature difference between your pool and the air — typically in spring and fall.
Should I get a heat pump or stick with my gas heater?
Heat pumps have a much higher COP (often 5.0–6.0) than the efficiency of gas heaters (typically 0.80–0.85), which sounds amazing. But the comparison depends on your local electricity and gas prices and your climate.
Run the calculator twice — once with your current gas heater settings and once with a heat pump — using your actual utility rates. If electricity is cheap and your outdoor air stays above 50°F during your season, heat pumps win. If electricity is very expensive or you live in a cold climate where heat pumps weaken, gas may be cheaper. Also consider installation cost — heat pumps cost more upfront.
What if I do not know my heater's efficiency rating?
Check your heater's nameplate (stamped metal tag) or owner's manual — efficiency is usually listed as a percentage or decimal. If you cannot find it, typical values are gas heaters 0.80–0.85, electric resistance 1.0 (always), and heat pumps 5.0–6.0 COP.
If you are still stuck, call your heater manufacturer with the model number or contact a local pool service company. Do not guess — efficiency has a huge impact on your Total Seasonal Heating Cost. A 10% difference in efficiency changes your annual bill by hundreds of dollars.
Why does outdoor air temperature matter so much?
Heat always flows from warm to cold. The bigger the difference between your warm pool and the cold air around it, the faster heat escapes. If your pool is 82°F and the air is 50°F, there is a 32-degree gap and you lose heat very quickly. If the air is 75°F, that gap is only 7 degrees and losses are much smaller.
Daily Heat Loss uses this temperature difference in its calculation — a 10-degree difference means 10 times less loss than a 100-degree difference. Use your average outdoor temperature for the months you heat, not the record high or low. Check historical weather data for your region online.