# Pool Heater Calculator Pool heater size calculator for gas, electric, and heat pump models. Uses the standard Hayward pool heater size calculator formula and a pool heater BTU chart. Sizes Raypak and Pentair units too. ## What this calculates Size your pool heater correctly and you save thousands over the life of the unit. Undersize and it runs 24/7 without ever catching up. This pool heater calculator uses the industry-standard formula (surface area x temperature rise x 12) that Hayward, Pentair, and Raypak use in their sizing guides. Works for gas heaters, heat pumps, and electric resistance heaters. Covers above ground pools and in-ground pools of any shape. ## Inputs - **Pool Shape** — options: Rectangle, Round / Circular, Oval, Kidney / Freeform — Use Round for most above ground pools. - **Length (or Diameter)** (ft) — min 1, max 300 — Longest dimension. Enter the diameter for round pools. - **Width** (ft) — min 0, max 200 — Ignored for round pools. - **Average Depth** (ft) — min 1, max 20 — (Shallow + deep) / 2 for sloped pools. - **Current Water Temp** (°F) — min 30, max 100 — Starting temperature of the pool water. - **Target Water Temp** (°F) — min 60, max 104 — Most swimmers prefer 78-84 F. - **Desired Heat-Up Time** (hours) — min 4, max 72 — Hours to go from current to target. 24 hours is a typical target. - **Using a Solar Cover?** — options: No cover, Yes, solar cover / blanket — A cover cuts heat loss by about 50%. ## Outputs - **Pool Surface Area** - **Pool Volume** - **Gas Heater BTU/hr** — Hayward, Pentair, and Raypak gas heater sizing - **Recommended Gas Heater Model Size** — formatted as text — Nearest standard gas heater size - **Heat Pump BTU/hr** - **Electric Heater Size** — Electric resistance heater for small / above ground pools - **One-Time Heat-Up Cost (gas)** — formatted as text — Rough gas cost to bring water to target, at $1.50/therm ## Details Pool Heater Size Formula (Gas) The industry-standard pool heater size calculator formula used by Hayward, Pentair, and Raypak is: - BTU/hr needed = Pool Surface Area (sq ft) x Temperature Rise (F) x 12 - With a solar cover, multiply by 6 instead of 12 (cover cuts evaporative loss roughly in half). Example: a 16 x 32 ft rectangular pool has 512 sq ft of surface area. To raise water 20 F in a reasonable time: 512 x 20 x 12 = 122,880 BTU/hr, so you'd pick a 150,000 BTU heater from the gas heater range. Pool Heater BTU Chart This pool heater btu chart shows the typical heater size (BTU/hr) needed for common pool surface areas and a 20 F temperature rise with no cover: | Pool Size | Surface Area | BTU/hr (no cover) | Typical Model | |---|---|---|---| | 12 x 24 ft rect | 288 sq ft | 70,000 | 100K BTU (Hayward H100) | | 14 x 28 ft rect | 392 sq ft | 95,000 | 100K BTU | | 16 x 32 ft rect | 512 sq ft | 123,000 | 150K BTU (Hayward H150) | | 18 x 36 ft rect | 648 sq ft | 155,000 | 200K BTU (Hayward H200) | | 20 x 40 ft rect | 800 sq ft | 192,000 | 200K BTU | | 24 ft round | 452 sq ft | 108,000 | 150K BTU | | 15 x 30 ft oval | 353 sq ft | 85,000 | 100K BTU | | 25 x 50 ft rect | 1,250 sq ft | 300,000 | 300K or 333K BTU | Pool Heater Size Chart by Heater Type The same temperature rise needs different heater sizes depending on the technology: - Natural gas / propane heater: BTU/hr = Surface Area x Temp Rise x 12. Fastest heat-up (24-48 hr), highest operating cost. - Heat pump: BTU/hr = Volume (gal) x 8.33 x Temp Rise / Desired Hours. Slower heat-up (2-5 days), lowest operating cost. - Electric resistance heater: kW = BTU/hr / 3412. Works only for small spas and above ground pools under 5,000 gallons. Very expensive to run on full-size pools. Hayward Pool Heater Size Calculator Notes The hayward pool heater size calculator (and pdf sizing chart) uses the same surface-area-times-rise-times-12 formula above, with an adjustment for cover use. A hayward pool heater size calculator pdf download from Hayward's technical literature matches the numbers this tool produces to within rounding. Raypak pool heater sizing calculator and pentair pool heater calculator use identical math because they all implement the same ASHRAE pool heat loss model. Above Ground Pool Heater Calculator An above ground pool heater calculator uses the same formula, but above ground pools are usually round or oval and sit fully exposed to wind, so heat loss runs slightly higher than in-ground. For above ground pool heater size calculator results, consider adding 15-20% to the gas BTU size to handle extra wind-driven evaporation. Small above ground pools under 10,000 gallons often use a small gas heater (100K BTU Hayward H100), an electric heat pump (65K-90K BTU), or even a 5.5-11 kW electric heater for quick heat. Electric Pool Heater Size Calculator An electric pool heater size calculator gives kW, not BTU. Conversion: 1 kW = 3,412 BTU/hr. A 20,000 gallon pool needing a 20 F rise in 24 hours needs about 20,000 x 8.33 x 20 / 24 = 139,000 BTU/hr, or about 41 kW. That is a very large electric heater and realistically you'd pick a heat pump instead. Small above ground pools (under 5,000 gallons) can use 5.5-11 kW electric heaters, which run about $1-2 per hour of use at $0.15/kWh. Pentair Pool Heater Calculator & Raypak Pool Heater Sizing Calculator A pentair pool heater calculator result will match a raypak pool heater sizing calculator result for the same pool because all three major manufacturers (Hayward, Pentair, Raypak) sell heaters in the same standard BTU sizes: 100K, 150K, 200K, 250K, 300K, 333K, 400K, and 500K. Pick the next size up from what the formula returns. If you are between a 150K and 200K, go with the 200K because it heats faster and runs less often, which means longer lifespan. ## Frequently Asked Questions **Q: What formula does a pool heater size calculator use?** A: The standard pool heater size calculator formula is Surface Area (sq ft) x Temperature Rise (F) x 12 = BTU/hr. A 16 x 32 ft pool (512 sq ft) raising 20 F needs 512 x 20 x 12 = 122,880 BTU/hr, so a 150K BTU heater is the right size. With a solar cover, use 6 instead of 12 because the cover cuts evaporation in half. **Q: Is this equivalent to a hayward pool heater size calculator?** A: Yes. The hayward pool heater size calculator and the hayward pool heater size calculator pdf use the exact same surface area x rise x 12 formula this tool uses. Pick the nearest size up from Hayward's lineup: H100 (100K BTU), H150 (150K BTU), H200 (200K BTU), H250 (250K BTU), H300 (300K BTU), H400 (400K BTU), or H500 (500K BTU). **Q: How is an electric pool heater size calculator different?** A: An electric pool heater size calculator gives kW instead of BTU. 1 kW equals 3,412 BTU/hr. A 10,000 gallon above ground pool that needs 50K BTU/hr converts to about 15 kW. Small pools under 5,000 gallons can use 5.5-11 kW resistance heaters; larger pools should go with heat pumps or gas heaters because resistance electric is too costly at residential kWh rates. **Q: What about a pentair pool heater calculator or raypak pool heater sizing calculator?** A: A pentair pool heater calculator and a raypak pool heater sizing calculator return the same BTU number as Hayward because all three brands use the same ASHRAE pool heat loss model and sell heaters in the same standard sizes (100K, 150K, 200K, 250K, 300K, 333K, 400K). Pick the next standard size up from what the formula returns; oversizing by one step gives faster heat-up with no downside. **Q: How do I use an above ground pool heater size calculator?** A: An above ground pool heater calculator uses the same formula as an in-ground heater, but above ground pools are more exposed to wind so add 15-20% extra capacity. A 24 ft round above ground pool (452 sq ft) raising 20 F needs about 452 x 20 x 12 = 108,000 BTU/hr, bumped up to 125K with the wind adjustment. A 150K BTU gas heater or a 110K heat pump covers it. **Q: Gas heater vs heat pump for a 15,000 gallon pool?** A: A gas heater heats a 15,000 gallon pool 20 F in about 24 hours at a fuel cost of roughly $25-40 per heat-up. A heat pump takes 2-5 days for the same rise but costs $10-20 per degree over the season. Gas wins for weekend/vacation pools that sit cold most of the time. Heat pumps win for daily-use pools where you maintain a steady 80 F all summer. --- Source: https://vastcalc.com/calculators/everyday/pool-heater Category: Everyday Life Last updated: 2026-04-08