Pool Heater & Spa Calculators
Estimate how long your heater takes to warm the pool, and how often to change spa water.
HEATER & SPA
Heater Warm-Up Time
Not sure? Use the pool volume calculator.
How many degrees you want to raise the water.
From the heater label. Common gas heaters: 250k–400k BTU.
Gas heaters run ~80%. Heat pumps differ and slow down in cold air.
Estimated Heating Time
-- hours
To raise the water that much
Estimate only. Real warm-up time runs longer with wind, cold air, or an uncovered pool;
a solar cover cuts heat loss a lot. Heat pumps in particular slow down as the air gets colder.
Spa Water-Change Frequency
Suggested Change Interval
-- days
Between full water changes
Rule of thumb: a common guide is spa volume ÷ (3 × daily bathers) days, and most
spas get a full change every 3–4 months regardless. Change sooner if the water won't balance or stay clear.
For educational purposes only — full disclaimer ↓