1 Bedrooms 1 Bathrooms Peak Flow: 3.5 GPM (13.2 L/min) 1 - 2 People

Tankless Water Heater Sizing for 1 Bedroom, 1 Bathroom Home

A standard 1 bedroom, 1 bathroom home requires a peak hot water capacity of 3.5 GPM to support 1 simultaneous shower plus concurrent kitchen or laundry fixtures. Compare with our Tankless Sizing Chart and master Water Heater Sizing Calculator.

Fuel Type Select

Brand Filter Brand

1. Groundwater & Target Temperatures ΔT = Target − Incoming

Incoming:

Winter Groundwater Temp

°F

Desired Output Temp

°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.

Occupants	Low Demand	Average Demand	High Demand
1–2 People	30 Gal (115 L)	40 Gal (150 L)	50 Gal (190 L)
3–4 People	40 Gal (150 L)	50 Gal (190 L)	65–75 Gal (245–285 L)
5+ People	50 Gal (190 L)	65–75 Gal (285 L)	80+ Gal (300+ L)

Climate Zone Sizing Matrix

1 Bed, 1 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 140,000 BTU/hr

Electric Power 20.5 kW

Recommended Unit Rating 4.5 GPM @ 35°F rise

Moderate Climate (Midwest / Mid-Atlantic)

Inlet: 55°F Rise (ΔT): 65°F

Required Gas BTU 114,000 BTU/hr

Electric Power 16.7 kW

Recommended Unit Rating 3.8 GPM @ 35°F rise

Warm Climate (South / Sunbelt)

Inlet: 70°F Rise (ΔT): 50°F

Required Gas BTU 87,500 BTU/hr

Electric Power 12.8 kW

Recommended Unit Rating 3.5 GPM @ 35°F rise

Fixture Demand Breakdown

Simultaneous Peak Load Calculation for 1 Bed, 1 Bath

How the 3.5 GPM peak simultaneous flow demand is calculated for 1 - 2 People:

1 Main Shower (2.0 GPM)
1 Kitchen Sink / Dishwasher (1.5 GPM)

Natural Gas / Propane

1/2" or 3/4" Gas Line (Up to 140,000 BTU input)

Electrical Panel

100-150 Amp main panel (Minimum 2x 40A DP breakers for 18-20 kW)

Tank Water Heater Alternative

30 Gallon Storage Tank

Home Size Navigation

Compare Other Home Layout Sizing

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

Overview Guide Complete Water Heater Sizing Chart Larger Home → 2 Bed 1 Bath Sizing

Expert FAQ Guide

1 Bed, 1 Bath Sizing FAQs

Common questions about water heater sizing for 1 bedroom homes.

2 Questions Answered

Q1 What size tankless water heater do I need for a 1 bedroom 1 bathroom home?

A 1 bed 1 bath house with 1-2 occupants needs a unit delivering at least 3.5 GPM at your local temperature rise. In cold climates, choose a 140k-160k BTU gas or 18-20 kW electric unit.

Q2 Can a 13 kW electric tankless water heater run a 1 bed 1 bath condo?

Only in warm climates (Florida, Texas, Southern CA) where ground water is 65°F+. In northern cold zones, a 13 kW unit will struggle during winter when incoming water is 40°F.

Rinnai RX199iN / RXP199iN

Rinnai RX160iN

Rinnai RX130iN

Rinnai V65iN

Rheem RTGH-95DVLN

Rheem RTGH-84DVLN

Rheem RTEX-27 (240V)

Rheem RTEX-18 (240V)

1 Bed, 1 Bath Water Heater Specs by Region

Simultaneous Peak Load Calculation for 1 Bed, 1 Bath

Compare Other Home Layout Sizing

1 Bed, 1 Bath Sizing FAQs

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