Tankless Water Heater Calculator
Size on-demand water heaters for any application
Fixtures for Simultaneous Use
Select fixtures that may run at the same time
Temperature Settings
Tankless Requirements
Required Flow Rate
--
Required BTU Input
--
Temperature Rise
--
Inlet Water Temp
--
Gas Line Size
--
--
Fixture Flow Rates
| Fixture | GPM | Temp (F) |
|---|---|---|
| Shower (Standard) | 2.0 | 105 |
| Shower (High Flow/Rain) | 3.5 | 105 |
| Bathtub Fill | 4.0 | 102 |
| Kitchen Sink | 1.5 | 110 |
| Bathroom Sink | 1.0 | 105 |
| Dishwasher | 1.5 | 140 |
| Washing Machine | 2.0 | 120 |
| Utility Sink | 2.5 | 110 |
Tankless Unit Sizing Guide
Gas Units
- 120,000 BTU: 3-4 GPM @ 70F rise
- 160,000 BTU: 5-6 GPM @ 70F rise
- 199,000 BTU: 7-8 GPM @ 70F rise
- 250,000 BTU: 9-10 GPM @ 70F rise
Electric Units
- 18 kW: 2-3 GPM @ 70F rise
- 24 kW: 3-4 GPM @ 70F rise
- 27 kW: 4-5 GPM @ 70F rise
- 36 kW: 5-6 GPM @ 70F rise
Inlet Temperatures
- South: 67-77F inlet
- Central: 55-66F inlet
- North: 42-54F inlet
- Northern: 35-41F inlet
Installation Considerations
Gas Line
3/4" min typical
May need 1" for 199K+ BTU
Venting
Direct vent or power vent
Cat III or IV stainless
Electric
100-150A service
May need panel upgrade
Code
NFGC, NEC, UPC
Permit required