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4 Bedrooms 3 Bathrooms Peak Flow: 8.5 GPM (32.2 L/min) 5 - 7 People

Tankless Water Heater Sizing for 4 Bedroom, 3 Bathroom Home

A standard 4 bedroom, 3 bathroom home requires a peak hot water capacity of 8.5 GPM to support 3 simultaneous showers plus concurrent kitchen or laundry fixtures. Compare with our Tankless Sizing Chart and master Water Heater Sizing Calculator.

1. Groundwater & Target Temperatures ΔT = Target − Incoming
Incoming:
°F
°F (120°F Code Standard)
2. Peak Hot Water Fixture Demand Select fixtures operating concurrently during morning rush
Active Fixture Type Qty Flow (GPM)
Standard Shower (2.0 GPM)
Bathroom Sink Faucet (1.0 GPM)
Kitchen Sink Faucet (1.5 GPM)
Bathtub Filler (4.0 GPM)
Dishwasher (1.5 GPM)
Clothes Washer (2.0 GPM)
Required Peak Tankless Flow Rate
6.0 GPM at 70°F Rise
Metric Equivalent: 22.7 L/min at 38.9°C Rise
Required Heating Power 210,000 BTU/hr 61.5 kW Power
Groundwater Temperature Rise 70°F 50°F in → 120°F out
Estimated Electrical Draw 256 Amps 240V Dedicated Electrical Service
Total Connected Fixture Capacity 15.0 GPM If all home fixtures opened simultaneously

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.

Dynamic Flow vs. Temperature Rise Matrix Required BTU/hr (kW)
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)
Highlighted cell indicates your exact calculated demand requirement.
Recommended Compatible Water Heater Models Matches Your Exact Load
RINNAI

Rinnai RX199iN / RXP199iN

SENSEI® RX Series (Condensing)
5.5 GPM at 70°F Rise (11.1 GPM max)
199,000 BTU/hr 0.98 UEF GAS

Best for large households (3-4 simultaneous showers in cold climates).

RINNAI

Rinnai RX160iN

SENSEI® RX Series (Condensing)
4.4 GPM at 70°F Rise (9 GPM max)
160,000 BTU/hr 0.97 UEF GAS

Ideal for standard 2-3 bathroom homes with moderate to cold groundwater.

RINNAI

Rinnai RX130iN

SENSEI® RX Series (Condensing)
3.6 GPM at 70°F Rise (7 GPM max)
130,000 BTU/hr 0.96 UEF GAS

Ideal for 1-2 bathroom homes or warmer climate zones.

RINNAI

Rinnai V65iN

High Efficiency Plus (Non-Condensing)
3.8 GPM at 70°F Rise (6.5 GPM max)
150,000 BTU/hr 0.82 UEF GAS

Cost-effective non-condensing gas solution for small-to-medium demand.

RHEEM

Rheem RTGH-95DVLN

Performance Platinum® Condensing Gas
5.3 GPM at 70°F Rise (9.5 GPM max)
199,900 BTU/hr 0.93 UEF GAS

High-output gas unit supporting up to 3-4 simultaneous showers.

RHEEM

Rheem RTGH-84DVLN

Performance Platinum® Condensing Gas
4.7 GPM at 70°F Rise (8.4 GPM max)
180,000 BTU/hr 0.93 UEF GAS

Efficient mid-size whole-house gas tankless for 2-3 bathrooms.

RHEEM

Rheem RTEX-27 (240V)

Performance® Electric Tankless
2.6 GPM at 70°F Rise (6.6 GPM max)
27.0 kW (112.5A) 0.99 Energy Factor ELECTRIC

High-power whole-house electric unit (Requires 3x 40A double-pole breakers).

RHEEM

Rheem RTEX-18 (240V)

Performance® Electric Tankless
1.8 GPM at 70°F Rise (4.4 GPM max)
18.0 kW (75A) 0.99 Energy Factor ELECTRIC

Compact electric unit for 1-2 bathroom apartments or warm southern climates.

Climate Zone Sizing Matrix

4 Bed, 3 Bath Water Heater Specs by Region

Required heating capacity changes drastically depending on your local incoming groundwater temperature.

Cold Climate (North / Canada)
Inlet: 40°F Rise (ΔT): 80°F
Required Gas BTU 250,000 BTU/hr
Electric Power 45 kW
Recommended Unit Rating 11 GPM @ 35°F rise
Moderate Climate (Midwest / Mid-Atlantic)
Inlet: 55°F Rise (ΔT): 65°F
Required Gas BTU 199,900 BTU/hr
Electric Power 40.5 kW
Recommended Unit Rating 9.5 GPM @ 35°F rise
Warm Climate (South / Sunbelt)
Inlet: 70°F Rise (ΔT): 50°F
Required Gas BTU 199,000 BTU/hr
Electric Power 31.1 kW
Recommended Unit Rating 8.5 GPM @ 35°F rise
Fixture Demand Breakdown

Simultaneous Peak Load Calculation for 4 Bed, 3 Bath

How the 8.5 GPM peak simultaneous flow demand is calculated for 5 - 7 People:

  • 3 Simultaneous Showers (6.0 GPM)
  • 1 Kitchen Sink (1.5 GPM)
  • 1 Dishwasher (1.0 GPM)
Total Combined Simultaneous Flow: 8.5 Gallons Per Minute (32.2 L/min)
Natural Gas / Propane
1" Gas Line or Cascaded Dual 3/4" Lines (199k - 250k BTU)
Electrical Panel
300-400 Amp service (Dual 24 kW electric units or commercial gas)
Tank Water Heater Alternative
75 Gallon Storage Tank
Home Size Navigation

Compare Other Home Layout Sizing

Explore water heater sizing calculations for different bedroom and bathroom counts.

← Smaller Home 4 Bed 2.5 Bath Sizing Overview Guide Complete Water Heater Sizing Chart Larger Home → 5 Bed 3 Bath Sizing
Expert FAQ Guide

4 Bed, 3 Bath Sizing FAQs

Common questions about water heater sizing for 4 bedroom homes.

1 Questions Answered
Q1 Can one tankless water heater run 3 showers at once?

In warm climates (inlet 65°F+), a single 199k BTU condensing gas heater (9.5-11 GPM) can support 3 simultaneous showers. In northern cold climates, running 3 showers requires either dual cascaded 160k-199k BTU units or a commercial-grade 250k+ BTU unit.

Water Heater Suite

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Quick visual sizing tables matching groundwater temperature zones with GPM fixture loads.

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