TL;DR
A whole-house tankless water heater typically delivers 6-10 GPM at a 60-70°F temperature rise. A 2-bathroom home with 3-4 occupants needs 6-7 GPM. A 3-bathroom home with 5+ occupants needs 8-10 GPM. Sizing is determined by counting fixtures that may run simultaneously, not by household size alone.
How tankless GPM is measured
Unlike tank water heaters (sized by FHR), tankless water heaters are sized by GPM (gallons per minute) — how much hot water they can deliver on demand, at a given temperature rise. A tankless rated for 9 GPM at a 35°F rise may only deliver 6 GPM at a 65°F rise (the typical cold-to-hot temperature difference in northern US homes).
The temperature rise is critical: if your groundwater is 50°F and you want 120°F output, you need a 70°F rise. The same heater will deliver more GPM in Florida (groundwater 70°F, 50°F rise) than in Maine (groundwater 45°F, 75°F rise).
Manufacturer spec sheets always list GPM at multiple temperature rises. Use the rise that matches your climate.
Top picks for this size
EcoSmart ECO 11 Electric Tankless Water Heater, 13KW at 240 Volts with Patented Self Modulating Technology #ad
★★★★ 4.1 · 5K+ · $244
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EcoSmart ECO 27 Electric Tankless Water Heater, 27 KW at 240 Volts, 112.5 Amps with Patented Self Modulating Technology, 17 x 17 x 3.5, White #ad
★★★★☆ 4.5 · 3K+ · $475
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Ecosmart ECO 24 24 KW at 240-Volt Electric Tankless Water Heater with Patented Self Modulating Technology, 17 x 17 x 3.5 #ad
★★★★☆ 4.7 · 337+ · $501
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Rheem 18kW 240V Tankless Electric Water Heater, Gray #ad
★★★★ 4.2 · 4K+ · $438
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Rheem RTEX-24 24kW 240V Electric Tankless Water Heater, Gray #ad
★★★★ 4.1 · 4K+ · $546
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Rheem 11kW 240V Tankless Electric Water Heater #ad
★★★★☆ 4.7 · 4K+ · $255
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Rheem 240V Heating Chamber RTEX-13 Residential Tankless Water Heater, GRAY #ad
★★★★ 4.4 · 1K+ · $273
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Stiebel Eltron Tankless Water Heater – Tempra 29 Plus – Electric, 28.8kW, On Demand Hot Water, Eco, White, Made in Germany #ad
★★★★ 4.2 · 446+ · $695
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Stiebel Eltron Tankless Water Heater – Tempra 24 Trend – Electric, 24kW, On Demand Hot Water, Eco, White, Made in Germany #ad
★★★★ 4.2 · 90 · $620
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Rinnai V53DeN Natural Gas Tankless Water Heater - 5.3 GPM, Outdoor Installation #ad
★★★★ 4.2 · 230+ · $640
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Rinnai RE199iN Non-Condensing Natural Gas Tankless Water Heater, 199,000 BTU, 9.8 GPM On-Demand Hot Water, Indoor Whole House Installation #ad
★★★★ 4.2 · 39 · $1279
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EcoSmart ECOS 27 Tankless Electric Water Heater, 27 kW at 240 Volts, 112.5 Amps with Self Modulating Technology #ad
★★★★★ 5 · 13 · $420
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Rheem RTG-84XLN-3 High Efficiency Non-Condensing Outdoor Tankless Natural Gas Water Heater 8.4 GPM, 180,000 BTUs #ad
★★★★ 4.2 · 27 · $953
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Rheem RTG-70XLN-3 High Efficiency Non-Condensing Outdoor Tankless Natural Gas Water Heater, 7.0 GPM, Gray #ad
★★★★ 4.2 · 63 · $804
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Electric Tankless Water Heater SIVUATEK 24kW, 240V - On-Demand Hot Water for Whole House - ETL Certified, Self Modulating - Compact Design for Easy Installation - for 4 Point of Use Hot Water #ad
★★★★ 4.3 · 250+ · $275
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Ranein 18kW Electric Tankless Water Heater, 240V On Demand Instant Endless Water Heater with LED Temperature Display, Control Knob, Space Saving Design, Up to 4.3 GPM for Whole House Water #ad
★★★★ 4.4 · 361+ · $208
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Rheem 6.5kW 240V Point of Use Thermostatic Tankless Electric Water Heater #ad
★★★★ 4.2 · 4K+ · $189
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NEW Rinnai RX199iN Condensing Smart Sense Natural Gas or Propane Tankless Water Heater, Indoor or Outdoor Water Heater, Up to 11.1 GPM, 199,000 BTU #ad
★★★★ 4.2 · 137+ · $1533
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NEW Rinnai RXP199iN Smart Sense Condensing Tankless Water Heater, 199,000 BTU, Up to 11.1 GPM, Natural Gas or Propane, Indoor/Outdoor Installation, Built-In Recirculation Pump #ad
★★★★ 4.2 · 116+ · $1861
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Ranein Propane Gas Tankless Water Heater, Indoor Max 3.6 GPM, 80,000 BTU Instant Hot Water Heater #ad
★★★★ 4.4 · 618+ · $254
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A. O. Smith Tankless Water Heater Natural Gas - Endless Instant Hot Water up to 10 GPM - Integrated Recirculation Pump - Indoor Condensing 199,000 BTU ProLine® XE ATI-540P-N #ad
★★★★☆ 4.9 · · $1160
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A. O. Smith Tankless Water Heater - Natural Gas - 160,000 BTU - Endless Hot Water - Ultra-Low NOx - X3™ Scale Prevention - ProLine® XE ATI-240HX3-N #ad
★★★★☆ 4.9 · · $1300
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Electric Tankless Water Heater WINTEMP 27kW 240V, Whole House Hot Water Supply, On Demand Instant Endless Water Heater, with LED Temperature Display, WiFi Control, Up to 6.3 GPM, ETL Certified #ad
★★★★ 4.1 · 251+ · $340
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A. O. Smith Tankless Water Heater Natural Gas - Endless Instant Hot Water up to 10 GPM - Integrated Recirculation Pump - Indoor Condensing 199,000 BTU ProLine® XE ATI-540P-N #ad
★★★★ 4 · · $1160
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GASLAND Gasmart E 199,000 BTU Tankless Water Heater, Up to 7.6 GPM, CSA Certified Whole House Natural Gas Indoor Installation Residential On-demand Instant Hot Water Heater, CE686NG #ad
★★★★ 4.2 · 38 · $560
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Noritz GQ-C3261WX-FF US NG EZ Series Pro 11.1 GPM 199,900 BTU 120 Volt Residential Indoor/Outdoor Natural Gas Tankless Water Heater with Bluetooth Connectivity - Silver #ad
★★★★ 4.1 · 3 · $1799
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Westinghouse Tankless Water Heater Electric 14kW 240V, Instant On-Demand Hot Water, Smart WiFi, Compatible with Alexa & Google Home, ETL Certified IPX4, Space-Saving, Gray (APOLO-2.0 Upgrade) #ad
★★★★ 4.4 · 90 · $228
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Tankless Water Heater Natural Gas, 4.21 GPM 16L Indoor Instant Hot Water Heater with Digital Fahrenheit Display Multi-Protection Constant Temperature for Home & Apartment #ad
★★★★ 4.2 · 1 · $114
Amazon
These Amazon-available picks meet the calculated spec. For region-specific or licensed contractor-installed options, consult a local professional. See our Disclaimers.
GPM chart by household and simultaneous fixtures
Tankless GPM sizing by household
| Household | Typical GPM needed (60°F rise) | Tankless unit |
|---|
| 1-2 people, 1 bath | 3-5 GPM | Small point-of-use or 6 GPM whole-house |
| 3-4 people, 2 baths | 5-7 GPM | 7-8 GPM whole-house |
| 5-6 people, 3 baths | 7-9 GPM | 8-10 GPM whole-house (or two units) |
| 7+ people, 4+ baths | 9-12 GPM | Commercial-grade or two parallel units |
How to count simultaneous fixtures
Typical fixture GPM draw (with aerator):
- Shower (standard): 2.0-2.5 GPM
- Shower (low-flow): 1.5 GPM
- Kitchen faucet: 1.5-2.0 GPM
- Bathroom faucet: 0.5-1.0 GPM
- Dishwasher: 1.0-1.5 GPM
- Washing machine: 2.0-3.0 GPM (rarely runs while showering)
Add up the GPM of all fixtures that could run at the same time during your peak usage (typically: morning shower + kitchen cleanup + someone brushing teeth). That sum is your target tankless GPM, with 1-2 GPM margin.
For more on tank vs tankless tradeoffs, see our tank vs tankless comparison. Use our free water heater calculator for your specific household.
Frequently asked questions
What GPM tankless do I need for a family of 4?
A family of 4 with 2 bathrooms typically needs 6-8 GPM at a 60°F temperature rise. A 7-8 GPM whole-house tankless handles this with margin. If you live in a cold climate (groundwater below 50°F), size up to 9-10 GPM to account for the higher temperature rise.
Is 6 GPM enough for a house?
6 GPM is enough for a 1-2 bathroom, 1-3 person household. It supports one shower (2.0 GPM) plus a faucet (1.0 GPM) plus a dishwasher (1.5 GPM) = 4.5 GPM with 1.5 GPM margin. For 3+ bathrooms or 4+ people, go to 8+ GPM.
How many GPM is a typical shower?
A standard US shower head uses 2.0-2.5 GPM. Low-flow shower heads (mandatory in some states) use 1.5-1.8 GPM. Older shower heads (pre-1992) can use 3.5-5 GPM. If you're sizing a tankless, count your shower's actual GPM.