Homeowner planning tool
Water heater demand calculator
Explore simultaneous fixture flow and a separate household daily-use estimate. Neither result tells you which water heater to buy.
What might run at the same time?
Example: one shower and a sink running together in a household of 3 to 4 people. Change the selections to match your home. The flows are fixed reference values.
Example calculation
Hot-water demand
- Simultaneous fixture flow
- 4
- Estimated daily household use
- 30 to 80
Gallons per minute (GPM). Reference fixture flow, not measured hot-water flow.
Gallons per day. Separate from simultaneous flow.
Check every selection before using these figures. Tankless selection needs flow at the required temperature rise. Storage selection needs a first-hour demand assessment and the equipment’s first-hour rating.
ENERGY STAR rating definitions ↗What the result means
Assumptions and limits
Fixture values are reference flows, not measurements of your home’s hot-water demand. This model does not account for mixed-water temperatures, incoming water temperature or draw duration. Daily gallons are not tank size or first-hour rating.
Water heater servicesHow this calculator works
Reference fixture flows: each shower 2 GPM; bathtub 4; dishwasher 1.5; washing machine 2.5; sink 2. Selected flows are added. Household use uses the legacy assumption of 10 to 20 gallons per person per day across the selected household bracket. For 7+ people, 70+ is an open-ended lower reference, not an upper limit.
Before you decide
What your results mean
Use the result with its assumptions and limitations.
Why is household daily use different from heater sizing?
Daily gallons do not establish peak-hour storage/recovery or simultaneous tankless flow at a temperature rise. The tool’s fixture flows and daily-use brackets are reference assumptions, not measurements of your home. Use the result to discuss busy periods and installation conditions, not select a tank capacity or tankless model.
Does adding fixture flow select a tankless heater?
No. The required flow also depends on incoming-water temperature and the desired temperature rise. The reference fixture values do not measure your actual hot-water mix.
Does estimated daily use give the tank size?
No. Storage selection compares busy-period use with capacity and recovery or first-hour performance. Daily gallons and tank gallons are different quantities.
Your next step
Discuss your home’s equipment
Bring the estimate and your questions. Equipment selection needs more information about your home than a calculator can collect.
