Gas vs Electric

BruceN34 · Dec 9, 2019

I'm almost 70 and probably will only need one more water heater. There are two of us in our house and we currently have a 65 gallon natural gas unit that's 18 years old. I considered going tankless, but I doubt the extra costs in converting to larger gas pipe plus the cost of the unit would make sense. I was just going to buy a 75-80 gallon unit since the 65 barely allows my large jacuzzi tub to fill. A gas unit of that size runs around $850. I doubt that my HWH usage is more than around $25 in a cold month. Just today my electric utility sent me an offer to convert to a Rheem heat pump water heater which would cost around the same, except that I'd get wifi control, various sensors, etc. Seems like a good deal, but the real question is whether there would be any savings in making the conversion. FWIW, the unit is in a hugely well ventilated area and I could handle running an extra electrical circuit to the heater. Your thoughts?

Diehard · Dec 9, 2019

Based on your concerns to fill your jacuzzi, have you looked at comparing the recovery rates?

BruceN34 · Dec 9, 2019

Thank you, Diehard. Asa non-pro, i wasn’t thinking recovery rates, but the large tub would struggle with the above numbers much as it struggles now (I have to crank it all the way up, then wait half an hour before I can achieve an acceptable temp). I’ll just go with a 75 gallon gas which has a better rate for the first hour and way better for subsequent hours.

Diehard · Dec 9, 2019

Not sure if you noticed but the recovery rate shown above is based on a temperature rise of 90 degrees which is higher than what the gas units typically show for temp rise.
I found this A. O. Smith guide that may be of further assistance.

fixitron · Dec 10, 2019

The heat pump water heater is by far the most energy efficient, BUT they have a very slow recovery. They take the heat from the air around it (such as your basement) so that area will get cooler. In northern climates in winter that can be a problem, but in southern climates is where they shine. They use electricity to "pump" thermal energy from the air to the water. For every unit of electrical energy that is used by the "pump" 4-5 units of energy are moved to your water as heat. When the air around the heat pump water heater gets below roughly 60 degF, then the ratio of heat "pumped" decreases.
A tankless water heater, like any combustion appliance, is not very efficient when the hot water draws are frequent and short. They shine when there is a large demand for hot water, such as for filling a jetted tub or providing hot showers for several people in a short time. Tankless, or on-demand, water heaters require a much larger gas line and must be serviced every 1-2 years. Install, parts, maintenance and repair are much more expensive than a tank style heater.
The larger tank with a gas water heater would be my choice for your scenario.