Tankless Water Heater GPM Chart: Fixture Flow Rates by Appliance
Reference chartBased on ENERGY STAR fixture standards
Quick answer
Standard fixture GPM rates used for tankless sizing: shower 2.0 GPM (low-flow), kitchen sink 1.5 GPM, bathroom sink 1.0 GPM, dishwasher 1.0 GPM, washing machine 1.5 GPM. Sum the GPM of fixtures that might run simultaneously during peak use (typically morning). For a 4-person household, plan for 7-9 GPM total in moderate climate.
Fixture GPM Reference Table
Fixture
Standard GPM
Low-Flow GPM
Notes
Shower (standard 2.5 GPM head)
2.5 GPM
2.0 GPM
Default 2.0 GPM for tankless sizing
Shower (1.75 GPM head)
1.75 GPM
—
EPA WaterSense labeled
Kitchen sink
1.5 GPM
1.0 GPM
Aerator-restricted
Bathroom sink
1.0 GPM
0.5 GPM
Standard 1.0 GPM
Bathtub fill (standard)
5-6 GPM
—
Faster fill, but only momentary peak
Dishwasher
1.0-1.5 GPM
—
Draws during fill cycle only
Washing machine
1.5-2.0 GPM
—
Modern HE units use less
Outdoor hose bib
2.5-5 GPM
—
Cold only — doesn't count
Handheld shower
1.5-2.0 GPM
1.0 GPM
Often restricted
Standard GPM rates reflect post-1992 federal flow restrictor requirements. Some older homes have higher-flow fixtures (3-4 GPM showers); reduce to 2.0 GPM with EPA WaterSense showerheads.
Common Usage Scenarios
Scenario
Fixtures Running
Peak GPM
Recommended Tankless
1 adult morning shower
1 shower
2.0 GPM
3-4 GPM (small electric)
2 adults, sequential showers
1 shower at a time
2.0 GPM
3-4 GPM
2 adults, simultaneous showers
2 showers + bath sink
5.0 GPM
6-7 GPM gas
Family of 4, morning peak
2 showers + kitchen + bath sink
6.5-7.5 GPM
8-9 GPM gas
Family of 4 + dishwasher
2 showers + kitchen + DW
7.5-8.5 GPM
9-10 GPM gas
Family of 5+, simultaneous
3 showers + kitchen + laundry
10-11 GPM
11+ GPM or 2 units
US Climate Zone Inlet Temperatures
Cold (45°F inlet)
Northern states: Minnesota, Wisconsin, Maine, North Dakota, Michigan, New York (upstate), Vermont, New Hampshire, Massachusetts, Rhode Island, Connecticut, Pennsylvania, Ohio, Indiana, Illinois, Iowa, Nebraska, Colorado, Wyoming, Montana, Idaho, Washington (east), Oregon (east).
Moderate (55°F inlet)
Mid-Atlantic / Pacific NW: Virginia, Maryland, Delaware, New Jersey, New York (downstate), Washington (west), Oregon (west), Northern California, Kentucky, Tennessee, North Carolina (mountains).
Warm (65°F inlet)
Southern / Southwest: Florida, Georgia, South Carolina, Alabama, Mississippi, Louisiana, Texas, Arizona, New Mexico, Southern California, Nevada, Hawaii.
Cold-climate winter ground temps can be 10°F lower than summer — multiply your GPM requirement by 1.25 for safety margin in northern states.
Tankless GPM FAQ
How many GPM does a shower use?
Standard showerheads use 2.0-2.5 GPM. Low-flow (EPA WaterSense) showerheads use 1.5-1.75 GPM. For tankless sizing, use 2.0 GPM as the default per shower.
What is a typical dishwasher flow rate?
Most dishwashers use 1.0-1.5 GPM during the fill cycle only. The fill cycle lasts 30-60 seconds, so this is not a sustained draw — but it does count toward peak simultaneous demand.
How do I calculate peak GPM for my household?
Identify all fixtures that might run simultaneously during peak use (typically morning). Sum their GPM. Add 1.0 GPM safety buffer. For a 4-person household with 2 showers + kitchen: 2 + 2 + 1.5 = 5.5 GPM + 1 buffer = 6.5 GPM.
What if my inlet water is very cold?
In cold climates (inlet below 50°F), tankless units deliver less effective GPM. Derate the manufacturer's GPM by 20-30%.
Need an Exact GPM Recommendation?
Our free calculator factors in your fixture count, climate zone, and fuel type for a custom GPM and BTU/kW in 60 seconds.
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