I am in the process a purchasing a fixer upper. I plan on doing some significant energy retrofitting including new windows and exterior rigid foam insulation. The water heater and furnace are Natural Gas, with the addition of central AC. I dislike NG and plan on disconnecting the furnace and HWH regardless, probably the prepper in me (they models in the home are also old and notorious for failure).

My thought is to install a Hybrid Heat Pump Electric water heater from Rheem (I will be doing this regardless, temp goes up to 150). Then I would feed hydronic coils in my air handler with water from the water heater and a small efficient pump that is set to come on when the thermostats trigger heating. I would use the old water heater (disconnected) with thick insulation blankets on it as a storage tank which would collect water from the hydronic coils in the air handler and then this tank will feed the Rheem unit. The incoming cold water line would run through the old water tank first which would passively preheat the water before going to the heat pump tank(through hot water from the return line from the hydronic coils and somewhat the air temp), increasing efficiency.

I would also like to connect a heat exchanger from Aqua Systems Inc. between the cold water intake line and the old water heater, using the AC hot line for the heat. This would reduce my water heating load in the Summer. I could set the water heater temp high in the winter and "normal" in the summer. One of the things that needs "fixed" in this home is that the homeowner moved out and failed to pay the power bill, which caused all of the copper water lines to burst when they froze. All of the lines have already been removed so I need to replumb with PEX. Mixing valve/valves will me installed on the hot water line feeding sinks/showers/tubs to prevent burns.

Lastly I would duct the air inlet of the Water Heater to the outside with a changeover valve that would allow it to draw warm air seasonally either from outside or the utility room (which is conditioned space). The air outlet (cold air) would be dual ducted with a changeover valve, allowing the cold air to be vented either to the outside or the air handler ductwork cooling the home. My home will have rooftop solar comprised of as many panels will fit on south facing aspects, approximately 15 kW.

My questions are:

1) Is this practical and will it work?

2) What will my energy usage be for space heating compared to a new air source heat pump system to replace the old furnace and central air? Bear in mind that the new air source central heat pump unit would cost at a minimum $2,000 more to install than what I have described above. Thanks for the advice ladies and gents.

Reserved

Will this work? Not likely unless your home is tiny and insulated and air sealed well above code minimums. I checked the Rheem hybrid heat pump water heater specs and all that I found only have a 4200 BTU/h rated compressor output. That is pretty small. That is less heat output than a 1500W portable electric heater (5100 BTU). Can you heat your entire home with a single 1500W electric space heater?

Also, if you duct the heat pump cold discharge air outside during the winter, then the negative pressure inside the building envelope created by that exhaust will draw in outside cold air through leaks in your building envelop thus negating some of the heat generated by the heat pump. This would not be the case if you duct both the supply and discharge outside so that the effect on the building envelop pressure is neutral. However, output of the heat pump drawing in cold outside air would be negatively affected such that it would likely be well below 4200 BTU output.

IDK if this will work...

The recirculation pumps which force flow through the coils in the air handler run at 3 GPM. With a 50 Gal tank thats 14 minutes of continuous flow with a starting temp of 150 degrees, with an 80 gallon tank thats 27 ish minutes of continuous flow. Additionally, I could add a drain water heat recovery unit would preheat the incoming water and reducing the recovery time for the Rheem unit significantly.

The home is a split level with the upper half of the basement above ground level. I will be replacing all of the windows with U 20-25 units and then placing a continuous layer of R13 rigid insulation from the bottom of the footings to the soffit/roof. Seams will be taped. Attic insulation of around R50, higher if i can fit it. The home should be well insulated and pretty airtight, dramatically reducing the demand for heating.

I suppose I could try it and then put in the heat pump unit if it doesn't work. Same plumbing and wiring.

This is something I had previously not taken into account. I will need to think about how much of an impact this would have.

Actually, after thinking about this a bit more (not sure why I didn't think of this at first), the only way this would work at all is to duct your air supply and return lines from the heat pump outside of the conditioned space, and then only marginally due to low performance of the heat pump attempting to extract heat from cold outside air in winter. If your heat pump air duct is taking in air from the conditioned space and using that to heat water, this won't work at all. Other than the small losses in the heat pump motor due to the resistance of the windings which generates a small amount of heat, a heat pump just moves heat from one point to another. If you are using the air from the conditioned space to supply the heat pump, and then using the water heated by the heat pump to heat up the air, you aren't adding any heat to the conditioned space other than the small amount of losses previously mentioned - all you are doing is moving heat from the air near the water heater to the duct work.

If you want to heat and cool your space using a heat pump for the lost cost possible, you should look into ductless mini-split heat pumps.

The hybrid heat pump water heater would provide beneficial cooling and humidification in the summer though, assuming air intake and discharge is inside the conditioned space (it moves heat from the conditioned air to the water int the tank).

The first thing you need to do is understand what your heat loss/gain will be before you attempt to install a heating/cooling system. This is called a Manual J HVAC calc. There are free and low cost programs on-line that allow you to do the calculations yourself or there are professionals that do this for a fee - google [home energy rater] or [HERS rater]. Examples: http://www.loadcalc.net/ https://www.borstengineeringconstruction.com/Heat_Loss_Analysis_Calculator.html

Not sure what all I just read in this whole post.....but I think I see a train coming.