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. Gas supply, venting and combustion air are decided by a licensed plumber or gas installer under your local code, not by a listing.
Exact listing: Ranein Natural Gas Tankless Water Heater, 8.5 GPM, 190,000 BTU, Outdoor
Listing identifier: B0GJFPX2X3. View listing source.
Title identifies the seller's listing; it is not an independent performance test. Check the selected configuration, current price and seller on Amazon.