3. Energy Source. Fuel type, availability and cost can vary greatly depending on where you live, and the type of fuel used will affect the heater's size and energy efficiency. The two most common are fuel sources for on demand water heaters are electricity and natural gas/propane.
- Electric - Available to most everyone on grid in the United States. Often easier to install because no venting is required. May not be able to keep up with large temperature rises or high flow rates for whole house uses in colder climates.
- Natural Gas/Propane - Widely available. Requires venting, fuel tank, and fuel delivery or transportation. Can be sized for whole house use even in cold climates.
Calculating BTUs Required for On Demand Water Heater
We knew electric was out of the question, since electricity up here is expensive, and it might limit the homeowner from going off grid. Since most propane on demand water heaters are rated by BTUs, I just calculated how many BTUs would be needed. It is very simple to calculate BTUs -
1. Find Temperature Rise. Outlet Water Temperature - Inlet Water Temperature = Temperature Rise
2. Find Flow Rate. Add up all possible simulataneous points of use, results should be in GPM (gallons per minute).