Compare tankless water heaters by the flow rate their listings state, the fuel they burn and the temperature rise your climate demands — documented specifications, nothing invented.
Compare indoor natural gas units
The sizing guide
Simultaneous showers, inlet water temperature and the fuel already in the house decide more purchases than any brochure GPM. Our guides walk the arithmetic in order.
A gas tankless water heater is sized by the flow it must deliver at the temperature rise your inlet water demands: read the stated maximum GPM, the BTU/h input, the fuel (natural gas or propane) and whether the unit is listed for indoor or outdoor mounting.
A gas tankless water heater is sized by the flow it must deliver at the temperature rise your inlet water demands: read the stated maximum GPM, the BTU/h input, the fuel (natural gas or propane) and whether the unit is listed for indoor or outdoor mounting.
A gas tankless water heater is sized by the flow it must deliver at the temperature rise your inlet water demands: read the stated maximum GPM, the BTU/h input, the fuel (natural gas or propane) and whether the unit is listed for indoor or outdoor mounting.
A gas tankless water heater is sized by the flow it must deliver at the temperature rise your inlet water demands: read the stated maximum GPM, the BTU/h input, the fuel (natural gas or propane) and whether the unit is listed for indoor or outdoor mounting.
Two product families at two hookup costs: gas units for high simultaneous flow with venting and fuel lines, electric units for smaller demand where the panel can carry them.
Size your flow rate
Upkeep
The service parts that matter are the ones that let a plumber flush scale out of the heat exchanger every year. Check the connection size before ordering any of them.
Listings that state a GPM and a BTU/h input for indoor natural gas, with condensing designs identified.
Compare indoor natural gas units
Wall-mounted propane units listed for outdoor installation, compared on the flow and input their listings state.
Compare outdoor propane unitsAI-generated editorial illustrations. These scenes illustrate hot-water planning; they are not photographs of listed products or evidence of hands-on testing.
Our research approach
Our comparisons read the exact Amazon listing and its public review record. They are not hands-on product tests, and they give no installation instructions.
We report what a listing documents and say plainly where it stops. Confirm current details with the manufacturer and seller, and keep every gas, venting and electrical question with a licensed installer.
