gas on demand vs electric on demand

[Obie]

"Obie neglected to tell you that he's a raw-fooder and he only showers once a month."

It helps that my shower head is mounted about 3 ft from my heater outside.

And I'm a gear head grease monkey and require frequent showers.

[dobanion]

Oh yay, I get to geek out a bit on this one. I'm a engineer by trade, and efficiency and energy calculations are my idea of fun.

Almost every version of heat from electricity is really simple, running electric current through a circuit that turns that current directly into heat. Heat pumps are the exception, nearly everything else fits this description. Using heat in this way is technically "efficient" in that none of the energy is wasted, so it's 100% efficient. But you are taking high quality energy (electricity) and turning it into low quality energy (heat). You are essentially undoing the process that was done at the power plant, which was turning chemical energy (diesel), into mechanical energy (a engine), then finally turning a generator to make electrical energy. This process is probably 30-40% efficient, in that 30-40% of the CHEMICAL energy in the fuel at the start successfully turned into ELECTRICAL energy at the end. Then, somebody turns on a electric heater and undoes the process.

You can do the math to turn electricity into BTUs (a measure of energy), I think a kilowatt/hour (kWh) is 3414 BTUs. A gallon of propane is about 90,000 BTUs. You can do the deep dive, but I promise, a propane BTU is gonna be somewhere around half the cost of a electrical BTU. So, a propane heater is gonna be cheaper than a electric heater over time.

Notice I said heat pumps were the exception. You aren't taking the electricity and turning it into heat, rather, you are using electricity to create mechanical energy (a compressor), and that process allows you to "pump" heat out of the air, and discharge that heat elsewhere. You can discharge that heat into water if you want, in which case we call it a "heat pump water heater." You end up netting more heat this way. You may see a rating of EER on heat pumps, this is the ratio of how much more heat you get using a heat pump rather than just turning it electricity directly into heat. A typical ERR of 3 means I can get 3x as much heat from a pump than a space heater with the same electricity.

Oh, and the higher the temperature of the air, the easier it is for you to pump the heat out of it, and the ERR tends to get a little better. For these reasons, if you can swing the initial cost, a heat pump water heater makes a lot of sense in Hawaii.

[terracore]

When they changed the rules in Hawaii so no more resistance tank heaters could be used in new homes most of the new construction seemed to be solar hot water. Now all I see is heat pump. I'm guessing it's the up-front cost to the builder.

The heat pump variety has to vent the cold air somewhere. Depending on how you configure one you could probably push that into your living space, so you could get some collateral climate control with your hot water.

[Obie]

They also dehumidify the air. I would install it in a good sized closet or in a louvered door closet in the bedroom.