I just got an AO Smith hybrid water heater installed. The 80 gallon model has an estimated annual operating cost of $190. The old style water heater that was 11 years old that it replaced had an estimated annual cost of $592. I bought the floor unit for $980, and the standard electric model was $625. The hybrid unit is going to pay for itself in less than a year! When my OWB goes in, I’m going to heat my hot water in the winter months too with it. But it’s nice knowing that the non-OWB months are only going to cost me about $13-14.
Heat pump heaters can also add some AC & dehumidification effect. Extra bonus in the summer. I had seriously misunderstood how efficient an electric water heater was, for the 17 years I was doing it with our oil boiler. Until I made the switch & observed for myself. I should have done it years ago. I did some extra things like get it on a stand with insulation underneath, and an extra layer of insulation around it everywhere else. Plus plumbed in an extra heat trap at the top. But it was costing me between 3/4 & 1 gallon of oil a day the other way.
I can definitely relate about things becoming a drag the older we get!! Our outdoor burner is currently not in service. Giving it & myself a break from feeding it. The storage of extra water sounds like a great idea although I’m not sure about best location, volume & things like that. I’m wondering if adding more water storage to my current system would reduce wood consumption and pay for itself over time. A new unit is not really in our budget till we get our daughter through college. Once again I thank everyone for all your insight on this topic!!!
Kevin, my plan is to install the Bradford-White version of that unit. I have my OWB and an Amtrol 40-gallon indirect tank, and I want to replace the indirect tank with the heat pump electric unit. I am struggling with figuring out how to hook it up, though. I can picture doing a direct swap with a simple plate exchanger on the inlet side of the water heater, the OWB will preheat the domestic water. Technically the electric unit will always be "on" but won't have to work very hard if at all. It will function as an indirect tank during OWB season and as a heat pump electric tank during the summer. Where I am lost, is how to use the electric unit as backup HEAT during the winter if I have to go away for any length of time, or I am somehow incapacitated. I am not concerned with the cost of using an electric heat pump unit for space heating, as it would only be for backup or emergencies. It would have to involve manual valve operation somehow, maybe an additional circulator pump. I just don't see how to do it.
You're talking about a DHW heater? And trying to use it to heat your house? Not exactly clear on what you posted, but I don't think that would work at all.
From reading the post above, I’m also not clear on what you’re going for- I don’t think the heat pump water unit would work for any sort of home or space heating. As far as backup water heat, it just kicks on when the OWB isn’t supplying hot water through the water/water heat exchanger, right?
That's exactly what I'm going for. I know that electric water heaters, of any kind, are not designed for space heating. However, most homes also have some kind of boiler or furnace that provides space heating in the winter. For example, my brother lives nearby and he spends most of his winters in Florida and Georgia. He has a propane boiler that keeps his house at 50° and prevents the pipes from freezing. I would need to do the same thing with my system, but use the heat pump to provide enough hot water during a short vacation (5-7 days) to keep the house from freezing. I know this can be done - whether it's a good idea or an efficient use of an electric water heater is another argument entirely. All of my heating is by circulator pumps and radiant in-floor tubing, so there has to be a way to allow the electric water heater to provide a minimum amount of hot water to the heating system to keep the house temps above 50°. Won't be any demand for domestic hot water anyway during that time. I do not want to do what has been suggested to me in the past, which is to put in an actual propane boiler (even one of the high-efficiency condensing units). I would still have to replace my indirect tank (it's got pinholes and is failing structurally) and a new propane boiler is a lot more expensive in both materials and labor. I didn't design the house to accommodate one either, so it would be a significant redesign of my mechanical room and all of the plumbing.
You are completely losing me on that idea. The HPWH is just a heat mover - it takes heat from one place, and puts it in another. When heating DHW, it takes it from the house air, and puts it in the DHW tank. Sounds like in your case, you would be taking it from the house air, and putting it into the house air. Where is the gain in heat coming from? EDIT: Unless, I guess, you mean you would use the resistance elements in the HPWH to add the heat? In that case - I'm not sure how you would do that either. I think it's a general no-no to mix DHW & heating system fluids. EDIT AGAIN: I guess a heat exchanger might help with that - but still not getting my head around how it could be done.
Nope, I want to take the hot water in the HPWH tank, and put it into the hot water manifold that supplies the radiant floor heat. In place of the wood boiler supply. In most cases, when people install an outdoor wood boiler, they are adding it as a secondary heat source - basically a way to preheat the water that is going into the house's domestic and heating systems. There is already a primary heat source in place, usually a gas or oil boiler, with an indirect tank. The primary boiler heats the water in the indirect tank for DHW, and uses a direct feed with a mixing valve to distribute hot water to heating systems. When a wood boiler is plumbed into some part of the system that allows it to take over the heating load during the winter months, you can usually take the primary boiler offline. Some people only use a wood boiler for heat, other have it set up to provide both heat and hot water, and it's usually just a variation in plumbing. In my case, it's backwards. My wood boiler is not just my primary, but my only system. I have my wood boiler feeding a plate exchanger, that in turn feeds a loop with six zones - five for heat and one for hot water. The hot water zone is fed by an indirect tank that has its' own built-in coil heat exchanger, internally. So heating system water and domestic water never mix. There is a circ pump and a mixing valve on each loop as well. I have no backup, no secondary, no nothing. Which is why I cannot leave my wood boiler unattended during the winter, why I cannot run out of firewood, why I burn 24/7/365 and have done so for 13 years. I have nothing else. What I want to do now, is use that heat pump water heater for both heating and domestic hot water during the summer and during short vacations in the winter (or an emergency). It's an odd situation. I need basically two completely separate primary systems - one for summer DHW and for winter heat backup (the HPWH) and one for winter DHW and heating (the OWB). They can be operated separately and by manual valves, or they can be tied together and operated automatically, or some combination thereof. Doesn't matter to me. What throws a wrench into my gears, is that I also need to use the HPWH as my indirect tank when the OWB is in use. Just can't figure it out.
Yes but [again ] - the heat pump doesn't make heat. It just moves it around. So you would have it in one place in your house, taking heat out of the air, and eventually that heat would show back up in another place in your house - which sounds like the in floor heat. So the house won't be getting heated. No new heat is being made.
A heat pump water heater pulls heat from the air and puts it into the water. If you are using the hot water to take a shower, great. But if you are going to use it to heat the house, then all you've done is gone in a big loop (as in dog chasing tail) unless the load is high enough that the electric resistance coils had to kick on to keep up...then there has been some new heat added to the system/loop...otherwise its air to water, water to air, air to water, water to air...all you've accomplished is run your electric bill up...and the house has actually gotten colder in the meantime. From what I have read on HPWH, if they are in an unheated basement, it will make the basement even colder (and drier) When my electric heater pops I'd like to try a HPWH...I think it would work out well with the heat of the wood furnace down there...and I run a de-humidifier all summer anyways so...
Oh, I get what you guys are saying. Yes I understand that the heat pump pulls heat from the air and puts it in the water. This will be of great benefit in the summer because it will cool my basement and dehumidify it as well. However, in the winter, I will have to switch the HPWH over to use the electric resistance coils in the unit, if I ever need it for heating or hot water. It would be manually switched over to function as a standard water heater. They all are set up to do that. That's when the electric bill goes up a bit, but remember I am only planning on using this for a few days or a week at most during heating season. The rest of the time, the HPWH will just function as an indirect hot water tank. If I were ever to sell my house, or somehow become unable to operate my wood boiler, that's when it all gets removed and we just install a high-efficiency condensing boiler and be done with it. That may happen anyway in 10-15 years when the heat pump unit decides to quit.
If you wanted to use electric for backup hear, I would likely just plumb in a small electric boiler. That's what I have. Take up very little space & pretty easy to install. Mine is an 18kw. I ended up with that one because I found it used at a good price. I could likely get away with a 9kw unit. I don't think I would try to do it with a DHW heater. There are some around here that are using them to keep their garage warm (barely above freezing) all winter but that's all they're used for. And it's likely taxing their limits at that. It's also expensive business fuel wise. I figure ours runs around $25-30/day to keep our house warm. It only gets used a couple days a year. If I needed backup that was used more frequently, I'd likely need to add an oil boiler. Or if I already had propane here, it would be that.
Since you’re looking for a solution that would only be needed at most for a few days a year, and not for serious heat but just to keep the place from freezing up in the winter, I wonder if a rocket mass heater might be a viable alternative...heat it up, and according to what I read it can release heat that has been stored in the mass for (up to) several days. Maybe BrianK could chime in on this one?
I talked to a dealer and he said he sells the same old style units and you just tell him its for your "business." What you hook it up to after you buy it is your own business. some laws were written with enough loopholes that they changed nothing. Buts that's none of my business.
How are you going to set it up to be heated by your OWB? Im curious about this, it would be a great setup for me as well. Right now my OWB heats my hot water all winter...my OWB just simply loops between the boiler and a heat exchanger, and my hot water tank just acts as a "zone" essentially...when it needs heat it kicks its circulator pump on and circulates through the heat exchanger picking up heat (as do all the zones in the house). In summer I open/close a few valves and the propane boiler is now circulating through the heat exchanger and all the zones (hot water tank included) just pull heat that way. I'd love to have one of these heat pump hybrids that runs on an efficient heat pump system all summer, then swap to my OWB in winter. At that point I'd officially be using zero propane (except for cooking and a standby generator).
It sounds like you already have as close to a “plug and play” setup as you can get. I’m going to do the same thing as you where the OWB will go to the water to air heat exchanger at the furnace, and then a water to water heat exchanger at the water heater. Since the water will be heated from the OWB, the unit at the top of my water heater won’t kick on. When the time of year comes to shut down the boiler, I’ll close the valve off and it’ll be back to business as usual where the heat pump on the water heater takes over again to heat the domestic hot water.
It would work much better if you recirculate the DHW side of the heat exchanger thru the DHW tank as needed. To charge up the DHW tank. Otherwise, hot water will only enter the DHW tank, when hot water is being used. If much is being used at a time or if it is a while between uses, the DHW might not get heated enough for what is being used or might not keep up. That might be what you're planning, not sure. It might also be possible not recirculating might work good enough but it might be marginal & you'd likely not know for sure without trying it.
