TanklesslyEndless hot water, sized to your fixtures.

Sizing

Tankless water heater for a three-bathroom house

Three showers at once is about 6 GPM; at a cold winter rise that takes a large condensing gas unit or two units.

By Tanklessly Editorial · Updated October 2026

The short answer

Three bathrooms rarely means three showers at once, but plan for it if mornings overlap: three 2 GPM showers is 6 GPM, plus 2 GPM if the dishwasher runs. With 47°F winter water (a 73°F rise) a 199,000 BTU condensing unit holds about 5.2 GPM, so three showers at once in winter calls for two units or a smaller set of fixtures. With 67°F water (a 53°F rise) the same unit holds about 7.1 GPM.

Electric?

A 36 kW electric unit holds about 4.6 GPM at a 53°F rise and 3.4 GPM at a 73°F rise, and draws 150 amps: workable for three bathrooms only in a mild climate with modest overlap.

Large units

Rheem RTGH-95DVLN-3 199,900 BTU Natural Gas Condensing Tankless Water Heater, Rinnai CX199iN 199,000 BTU Condensing Tankless Water Heater and Rinnai RX199iN Condensing Tankless Water Heater.

Products mentioned

Condensing gas tankless · Rheem

Rheem RTGH-95DVLN-3 199,900 BTU Natural Gas Condensing Tankless Water Heater

199,900 BTU/h · 9.5 GPM max

Rheem
Condensing gas tankless · Rinnai

Rinnai CX199iN 199,000 BTU Condensing Tankless Water Heater

199,000 BTU/h · 11.1 GPM max · Propane

Rinnai
Condensing gas tankless · Rinnai

Rinnai RX199iN Condensing Tankless Water Heater

199,000 BTU/h · 11.0 GPM max · Propane

Rinnai

Questions readers ask

What size tankless water heater for 3 bathrooms?
Plan for the showers that run together: two at once needs about 4 GPM at your winter rise, three needs 6 GPM. Large condensing gas units cover two in cold climates and three in mild ones.