Replace DHW Storage Tank with HeatPump Electric Water Heater
I currently have a new Weil McLain SGO4 oil fired boiler with a tankless water heater coil insert and 40 gallon storage tank. I replaced the boiler myself with a new burner, tankless coil, and modified the plumbing as needed in September of 2020. In the year prior after buying the house I replaced the leaking wet return buried beneath basement. See post linked for more information.
With the skyrocketing cost of home heating fuel seemingly overnight I am thinking about replacing my 40 gallon glass lined storage tank with a heatpump type electric water heater. I wanted to get your input on if this is a wise decision and if you have any suggests if I were to do so.
The storage tank has a 120v aquastat set for 145° that drives a taco circulator pump while the boiler has an aquastat set for 160° to fire the boiler. The boiler is also controlled by a Nest Thermostat for the steam house heat with a probe type LWCO, pressuretrol and automatic feed.
With the cost of oil suddenly at 5.30$/gallon and rising I was thinking of installing a heat pump type water heater. A Rheem 40 gallon heat pump electric water heater would cost around between 1600 and 1900$ minus a 750$ rebate from eversource. Bringing the cost down to 900-1200$ after tax.
I was thinking that there could be two options for doing this.
1. Plumb this in series with the tankless DHW coil insert replacing the 40 gallon storage tank. I could also add a tankless coil bypass with ball valves to bypass the coil in the winter when the boiler is running
2. Plumb the heatpump water heater in parallel with the storage tank with ball valves for isolation to use one or the other.
Would there be any advantages or disadvantages for doing one or the other? Currently my cold water feed comes in and tees into the boiler tankless coil. The water then runs through the coil in the boiler and up to the top of the tank with a circulator pump. The bottom of the storage tank then tees into the cold water supply and back into cold side of the coil with a check valve in the middle. The DHW for the house then comes off the storage tank into a taco thermostatic mixing valve and out to the house.
Could I replace the storage tank with the heat pump water heater? The cold water would feed through the boiler coil and into the cold side of the heat pump water heater and then out of the hot side to the thermostatic mixing valve and into the whole house? This way in the summer the boiler could be shut off with the water just running through the coil. And in the winter the coil will preheat the water before the water enters the heatpump water heater. Or I could plumb the water with ball valves to bypass the coil and not pull BTUs out of the boiler for the house heat
Or should I abandon the tankless hot water coil all together and just plumb the heatpump hot water completely separate from the boiler for DHW production?
What else could you suggest? Just trying to get the best setup and ideas. These kind of projects are really fun and interesting to me.
I have plenty of ampacity and space for a 240v breaker in the electrical panel. So this is not an issue.
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