Pool Heater Sizing and Heat-Up Time
The heater a pool needs, and how long it takes to come up to temperature.
Example
You enter
- Pool volume (gallons) 20000
- Temperature rise (°F) 10
- Heater nameplate INPUT (Btu/h; a heat pump: its heat output, with efficiency 1.0) 400000
- Efficiency as a fraction (0.80 gas; 1.0 for a heat pump entered at its heat output) 0.8
You get
- Heat-up energy 1,668,000 Btu
- Hours 5.2
Checked against published worked examples from: Aquaterra Outdoors (Raypak dealer).
Details, formula, and sources
ScopeHeat-up energy Btu = gallons x 8.34 x rise, and time = energy/(output x efficiency). A 20,000 gal pool +10 F takes 5.2 h on a 400,000 Btu/h gas heater at 80%, but 11.1 h on a 150,000 Btu/h heat pump. Ignores cover/standby losses. The equipment ratings govern.
Formula or tableQ_btu = gallons x 8.34 x dT; delivered = nameplate input x eff (the output key holds the INPUT rating); hours = Q_btu / delivered.
Source and editionThe sensible water-heating relation (1 Btu raises 1 lb of water 1 F), by name.
Free accessThe water-heating energy relation and the 8.34 lb/gal constant are standard published values. The equipment ratings and site conditions govern.
What governsEstimate. AHJ and licensed professional govern.
API field namesgallons, dT_F, output, eff, Q_btu, hours
- Sensible heat Btu = gallons x 8.34 x dT; 1 Btu raises 1 lb water 1 Fthermodynamics
- Heat-up time hours = energy / (output x efficiency); for a heat pump enter its heat output in Btu/h with efficiency 1.0, not its COPequipment ratings
- No standby loss ignores cover/evaporation/standby losses; real heat-up runs longerscope of this tile