- 2 elements are key for sizing and selecting a proper tankless water heater:
- Temperature of water source which varies according to location
- Demand of heated water: GPM demand depending on type and number of fixtures and appliances
- Taking this into account will prevent a lot of frustration on purchases and use
- The first support material we have available for this process is the Temperature Map:
- Note:
- The map indicates the capacity of the model units according to location
- Big difference in demand from a shower (1.5 to 2.0 GPM) and a bathtub (4.0 to 5.0 GPM)!
- The bathtub is the fixture that demands the highest GPM
- Difference in temperature of water source in the south and in the north
- Water source temperature also varies if from the city, well, tank, stream, etc. If water is exposed to air (well or tank situation) it is colder.
- The second support information is in the manual for each unit. There is a table that approximates the capacity of the water heater to raise temperature according GPM:
- Consider, the more the GPM (more water volume running through the unit) the less the temperature rise, the less the GPM the more the temperature rise
- Note tables consider a fixed temperature of water source or set temperature, so values are approximated
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Warning:
- GAS tankless water heaters do not work on high elevations/altitudes. As an industry rule of thumb, no tankless works properly above 4,000 ft. Marey units are not recommended above 2,000 ft. People use them on high elevation/altitude locations at their own risk, we do not recommend it. High altitudes do not have proper physical/environmental conditions for the combustion and exhaust processes of the units, in short, there is not enough air up there!
- Electric units are not affected by altitude