The heat pump water heaters work ok overall in the seattle area as long as they're installed correctly. Keep in mind the heat pump turns off if the outside air temp is below 20 degrees. If you see temps well below that the water heater will go back to using the backup heaters which will use a lot more power.

 

Thank you for your reply.

I have my Carrier heat pump set to shut down at 30 degrees when we switch to auxiliary heat via the LP-fired hydronic water heater.

Perhaps I am missing something but the heat pump water heater that I am considering is either an AOSmith or a Rheem. On both "hybrid" units, the compressor and evaporator are located on top of the water tank which would be located in our basement, next to the air handler and the LP-fired hydronic water heater. Should stay above 50 degrees in the basement in the winter so the heat pump should provide most of the heating (versus the 4,500 watt heating elements). Under this arrangement, are the outside temperatures relevant?

My main concern is the feasibility of "feeding" the HPWH with hot water from the LP-fired water heater in the event of a power outage as the hybrid unit cannot be connect to my generator but the LP-fired water heater will be.

 

I posted this initially in the plumbing forum but think that the Residential HVAC forum makes more sense.

I moved your posts from the plumbing forum to this duplicate thread. For future reference, when you want to change forums, just click on the small black triangle at the bottom of your post and ask to have it moved.

We would rather move it than have duplicate threads.

I deleted the thread in the Plumbing forum.

Thanks for your understanding.

 

Am I reading the question correctly? Are you asking if you can use the hydronic water heater to directly supply potable/drinking hot water by adding diversion valves to use either the hybrid or the hydronic water heater? In other words, when the need arises you will switch over and use the heated water directly from the hydronic water heater for you normal hot water needs.

No, you can not do this. Check with a master plumber if this would be allowed by code.

In a power outage situation with your size generator you should be able to add the HPWH with no problem I would think. Yes, you might have to be careful about what generator connected items you allow to run at the same time, but it is an emergency, and in those limited cases a little due diligence shutting off or not using some things why you're trying to make hot water would be an inconvenience at the most.

 

You are indeed reading the question correctly.

I appreciate the heads-up on a potential code violation - can you help me to understand the risk?

I have considered managing the draw as you suggest. My restriction may be more related to the panel capacity rather than kW capacity. I have attached a pic of my Generac panel - it appears full. You will note that my Carrier Heat Pump is not on the generator.

Perhaps some consolidation can be done as the draw from the various light fixture circuits (6, 8 & 11) is significantly less with our current LED bulbs versus the incandescent versions in use 20 years ago when the generator was installed?

 

Have you considered doing a hybrid approach? Replace the 75 gallon domestic water heater with 2 40 gallon heaters, one heat pump and one LP, piped in series with the heat pump water heater being the first in line. It'll do the bulk of the work and the LP water heater will only fire to maintain temperature because it's being fed hot water from the hp water heater. When the power goes out for an extended amount of time you'll still have the LP water heater to use because it's still tied into the generator power.

All this is assuming you have the space to have 3 water heaters in the basement.

 

The only way you could use a "heating boiler" for potable water is with a heat exchanger. Once water has been circulating through pipes and used for heating and possibly sitting in those pipes stagnant for several months or years, it needs to be kept as far away from the drinking water as possible.

Also, I don't really know a whole lot about heat pump water heaters, but 50° seems like it would be pretty close to being outside of it's normal operating envelope. I wouldn't expect it to work very well at those cold of temperatures. And as stated, it will also make the space around it colder as it's trying to suck the heat out of the room.

In your case I'd probably recommend straight electric, unless you are OK with paying all of the extra money for the heat pump one, and just planning to use it as a normal electric water heater when it gets cold outside.

 

How rural is your locale? I have a customer in rural SE Ohio who has solar panels. Several years ago the electric company told him that he was feeding too much back into their lines and they were going to stop paying him for generating excess power.
To consume that power, 6 years ago he bought a used Volt which they only use for errands around town. We made a rough calculation that his EV costs about $.03/mile. Compare that to ~$.17/mile for a gas vehicle.

 

Wow - tons of feedback. I thank you all.

Random responses...

1. The circuits that you see on my generator panel are the critical circuits - the ones that function when our power is out.

2. Our locale is very rural (Shenandoah Valley in VA). The most common vehicle around here is a pickup truck; second most common is probably a Subaru. We, of course, have an F-150 and an Outback. So, we really don't do errands around town. An EV makes sense in more urban areas but I just don't think that the rural infrastructure is there yet...maybe in 10 years. I'd love to have an F-150 Lightning - Super Cab / 6.5' bed - but they don't make that configuration. And at a cost of $75k, I can burn alot of gasoline, cheap or expensive.

3. I was concerned about the fact that the "heating boiler" is a closed-loop system...unless there is a leak somewhere, that same water has indeed been reheated for years. It makes perfect sense to keep it away from drinking water.

4. A straight electric water heater is the cheapest upfront outlay, especially if I downsize to a 50-gallon unit. Interestingly enough, the upfront cost of a 50-gallon heat pump water heater is 3X that of a straight electric water heater. At 75 gallons, the HP water heater cost increases by 50% (matching the capacity increase) but there really isn't many offerings for 75-gallon straight electric heaters. The few that I found were almost as pricey as the heat pump versions.

Given that there are just 2 of us here (when not hosting guests), I am thinking that a 50-gallon unit would be more than adequate. The straight electric version would consume the entirety of my 4 MW solar excess...but save me $1k of LP annually.

5. The idea of a putting (2) 40-gallon tanks - one LP and one HP - in series achieves my original objective but certainly in a different manner. I guess that I could keep both of my LP heaters and introduce a 40-gallon HP water heater in front the domestic water heater? That said, both LP tanks are 20 yo (as is the Generac). That seems to be an age where things start failing. An interesting concept that I need to think about.

Again, my thanks to all for your feedback.