heat pump water heater

can't your electric company do this?

I could do it if I knew approximately how much electricity my old one is using, but I don't.

On Sat, 21 Jun 2014 01:08:33 -0400, Judson McCranie wrote in

If you use a lot of hot water you are going to hate the HP heater. It has a long recovery time and reverts to resistance heating when there is a large HW demand. I estimate less than 5% reduction in electricity use, but that is just a guess.

Additionally, your locale is important.

Viz: In the Chicago area it would be pretty useless in the Winter.

In Phoenix it would make sense.

On Sat, 21 Jun 2014 05:10:21 -0500, philo  wrote in

BTW, the OP mentions $250 the utility will "give". Is that a rebate or credit against your electric bill? Or are the giving you the WH free plus a $250 credit?

Bottom line for me is that if they gave me the HPWH free plus a $250 credit, I still wouldn't take it.

Agreed, 17-y.o. appliances are not labelled to indicate consumption. But there now are many conservation organizations (some governmental, some voluntary) that ought to be able to tell you how much energy your old heater uses (per 100 gallons to 40 deg. C.): and there are even cheap meters you can interconnect between one appliance and the main supply.

ote

I'm sure there must be resources, articles, etc on the internet that discuss the advantages/disadvantages of a heat pump approach. I agree with the poster that said climate is going to make a big difference too. What works in Miami isn't going to work as well in MN. Given the increased cost of the more complex system, I'd be skeptical about the payback too. If they were a great idea, you'd see them a lot. I haven't seen one here in NJ.

Also, I assume nat gas isn't available, but if it was, it would be my first choice.

What cheap meter do you use to record the energy used by a

Your old one uses exactly 1 btu to heat 1 lb of water 1 degree F. Being electric you can consider it to be 100% efficient. Figure 3.4 BTU per watt. Figure 7.48 US gallons per cu ft/ and 62.6 lb per cu ft.

IF you have a 40 gallon heater and inlet temperature is 45 Deg F and thermostat is set at 140F, you are heating 5.34 cu ft of water by 95 F degrees, so you are using 5.34X95x62.6=31757 BTUs to heat the tank - aprox .935KwH of power if you take an hour to heat the water.

That's a rough calculation of the amount of electricity required to heat a tank of water.

Now I know someon's going to shoot holes through my calculations - that's a cast-in-stone and gold plated foregon conclusion.

What is important is the efficiency of the heat pump - or it's conversion factor - there is also another name for it that I can't remember - but basically how many watts of heat it puts out for every watt of electricity consumed. IF it is 140% efficient, you save 40% of the cost of heating your water. If it is 110% you save 10%. Then you need to figure out how long that heat-pump water heater needs to run between breakdowns in order for it to pay for itself in electricity cost savings. I hope you are under 50.

.935Kwh is .935kwh whether it takes an hour or 24 hours. And that would be a 935 watt heater running for an hour, which a quick reality check says isn't going to heat

Glad to oblige, but your process was correct, just a math mistake.

COP

IF it is 140% efficient, you save 40%

Looks like the COP for a WH is around 2+.

I'm actually surprised, I would have thought it would be at least 3.

So, bottom line you'd be heating for about 1/2 the cost. That assumes that the other side of the heat pump is somewhere like an unheated basement, where it doesn't matter if it cools it off or not.

Lowes has them for as little as $1000. Seems like it could have a reasonable payback period, depending of course on how much you use it, the electric rates. If they give you some big govt/utility rebate, it might make it very attractive.

philo  posted for all of us...

And I know how to SNIP

I believe the heat pump is mounted directly on top of the heater and uses surrounding air. No outside parts.

Seems to me I heard that GE now makes those water heaters. There must be a reasonable demand for them or GE wouldn't be in the marketplace.

I believe you are right.

Still...I would think they'd function better in Arizona where they are usually installed in a hot garage...than in a Northern location where they'd be in a cool basement.