The short answer
A propane tankless heater sizes exactly like a natural gas one: fixtures at once, winter rise, flow at that rise. The difference is supply. Propane carries about 91,452 BTU per gallon (EIA), so a 150,000 BTU unit burns about 1.6 gallons an hour at full fire and a 199,000 BTU unit about 2.2. The tank, regulator and line must deliver that alongside other propane appliances.
Propane use
| Input | Gallons an hour |
|---|---|
| 80,000 BTU/h | 0.9 |
| 100,000 BTU/h | 1.1 |
| 120,000 BTU/h | 1.3 |
| 150,000 BTU/h | 1.6 |
| 199,000 BTU/h | 2.2 |
Units in the catalog
Rheem RTG-95DVELP-3 199,900 BTU Propane Tankless Water Heater, Rheem RTGH-95DVLP-3 199,900 BTU Propane Tankless Water Heater and GASLAND CE686LP 199,000 BTU Propane Tankless Water Heater.
Fuel and conversion
SafetyPropane and natural gas units are different models (or need the maker's conversion). Never connect a unit to a gas it isn't built or converted for.
Products mentioned
Propane tankless · Rheem
Rheem RTG-95DVELP-3 199,900 BTU Propane Tankless Water Heater
199,900 BTU/h · 9.5 GPM max · Propane
Propane tankless · Rheem
Rheem RTGH-95DVLP-3 199,900 BTU Propane Tankless Water Heater
199,900 BTU/h · 9.5 GPM max · Propane
Propane tankless · GASLAND
GASLAND CE686LP 199,000 BTU Propane Tankless Water Heater
199,000 BTU/h · 7.6 GPM max · Propane
Questions readers ask
How much propane does a tankless water heater use?
At full fire, input BTU ÷ 91,452 gallons an hour: about 1.6 for a 150,000 BTU unit. It burns that only while hot water runs at full demand.