A standard 5 bedroom, 3 bathroom home requires a peak hot water capacity of 9 GPM to support 3 simultaneous showers plus concurrent kitchen or laundry fixtures. Compare with our Tankless Sizing Chart and master Water Heater Sizing Calculator.
Your peak simultaneous hot-water demand is 6.0 GPM (22.7 L/min) with a 70°F (38.9°C) temperature rise (incoming 50°F → desired 120°F). To deliver this flow reliably, your Gas tankless heater must produce approximately 210,000 BTU/hr (61.5 kW). Ensure the chosen model provides at least 6.0 GPM at a 70°F rise.
| Temperature Rise (ΔT) | 2.0 GPM | 3.0 GPM | 4.0 GPM | 5.0 GPM | 6.0 GPM |
|---|---|---|---|---|---|
| 40°F Rise | 40k BTU (11.7 kW) | 60k BTU (17.6 kW) | 80k BTU (23.4 kW) | 100k BTU (29.3 kW) | 120k BTU (35.2 kW) |
| 50°F Rise | 50k BTU (14.7 kW) | 75k BTU (22 kW) | 100k BTU (29.3 kW) | 125k BTU (36.6 kW) | 150k BTU (44 kW) |
| 60°F Rise | 60k BTU (17.6 kW) | 90k BTU (26.4 kW) | 120k BTU (35.2 kW) | 150k BTU (44 kW) | 180k BTU (52.8 kW) |
| 70°F Rise | 70k BTU (20.5 kW) | 105k BTU (30.8 kW) | 140k BTU (41 kW) | 175k BTU (51.3 kW) | 210k BTU (61.5 kW) |
| 80°F Rise | 80k BTU (23.4 kW) | 120k BTU (35.2 kW) | 160k BTU (46.9 kW) | 200k BTU (58.6 kW) | 240k BTU (70.3 kW) |
Best for large households (3-4 simultaneous showers in cold climates).
Ideal for standard 2-3 bathroom homes with moderate to cold groundwater.
Ideal for 1-2 bathroom homes or warmer climate zones.
Cost-effective non-condensing gas solution for small-to-medium demand.
High-output gas unit supporting up to 3-4 simultaneous showers.
Efficient mid-size whole-house gas tankless for 2-3 bathrooms.
High-power whole-house electric unit (Requires 3x 40A double-pole breakers).
Compact electric unit for 1-2 bathroom apartments or warm southern climates.
Required heating capacity changes drastically depending on your local incoming groundwater temperature.
How the 9 GPM peak simultaneous flow demand is calculated for 6 - 8 People:
Explore water heater sizing calculations for different bedroom and bathroom counts.
Common questions about water heater sizing for 5 bedroom homes.
A dual-unit cascaded gas tankless system (e.g., two Rinnai or Navien units linked with a communication cable) offers built-in redundancy, handles up to 18 GPM, and ensures infinite hot water for large families.
