Heat your water with a heat pump - 50% electric savings!

I have to amend my last post - they do in fact run the high (refrigerant) pressure line in your tank, dah don't know why I said otherwise. It is still an interesting concept. 2-5 year payback is not bad - then its free (if'n it don't break).

Adding the tax credit, the payback appears to be even quicker. I'm waiting to see what Mike's take is on this is before I put the trigger (thanks again Mike).

Well, I hope this works out, too. Glad to see there are so many people interested - whether for energy conservation or simply curiosity. If anyone wants any particular data (easy to get and low/no cost equipment), let me know here. Since I'm heating with wood, there are some pretty wild ambient air temperature fulctuations (anywhere from 55 F to 80 F). On top of that, I doubt that I will get the intake ductwork done right away (the plan is to take hot air from behind the wood stove).

I will most likely initially be able to give you a relative "chill factor" description where it will sit in the bathroom closet (it will be opened, of course). Once I get the kill-a-watt meter, I'll be more likely to be able to provide more useful information - like water temperature setting, inlet/outlet temperature, kWh/day, possibly run time/day. Let's keep our fingers crossed!

I too am waiting for a report. I have a basement that would be just right for this and use wood to keep the house somewhat warm. 63-68 depending on how high I keep the air adjusted.

My electric bill runs $100 or so with just 2 people that will soon be only one. Don't ask. I would like to cut it about 25% or more. I see my state of Indiana offers tax credit 2 times?

Shipper

So they got back to me - here's their response:

Interesting and reassuring stuff.

I looked at the energystar site, and...whoopie. Now my $300 tax credit is $209.70. Still a good incentive, I guess. I wonder if this "new" incentive is retroactive back to Jan. 1, or if the 30% thing starts on the day of the "stimulus".

Hate to say it, guys/gals, but I think we are all royally screwed in this whole situation. Assuming I make it through this thing and still have my house, the heat pumps/wood stoves/insulation/solar panels and everything else dealing with energy efficiency and self reliance are going to be my source of security. I guess that's why I'm investing in this sort of thing instead of the stock market. I had my reservations 15 years ago when I bought into this whole "retirement strategy"; I would have been better off buying cases of Old Milwaukee and saving the money from recycling the cans!

Mike,
Did you get it installed today?

I got the unit installed Saturday. Not any fault of the airtap, but it was initially a nightmare to install. You have to remove the hot water outlet nipple from the tank and replace it with one supplied with the unit. My new whirlpool 50-gallon tank had one installed at the factory (only extended out of the tank 1 ½”), and I ended up crushing it with a pipe wrench trying to get it out. I started thinking maybe it was tack welded or something, so I called the tech support – nope, threaded in there. I used a pipe wrench and 3’ cheater bar, so it was insanely torqued in there. I called lowes, explained the situation, and they said they’d take it back and give me a new one. I had to go with a 40-gallon tank since all of the 50s had pre-installed nipples (keep this whole thing in mind if you are considering one of these).

So after all of this, the installation went smoothly. I forgot to bring my data, but I took inlet temperature and then measured tank temperature about every half hour. The inlet was about 49 F, from what I remember. The air tap brought it up to 115 in about 3.5 hours.

It runs (so far) about 3 to 4 hours/day (say two hours of run time every 12 hours). I originally set the temp at 115 F, and when my daughter took a bath the first night, the water was only tepid. I called the tech support and was told that there is a 15 degree F temperature differential between on and off. So, I am assuming the temperature was about 100 F when my daughter took her bath, which would explain this. I have since cranked up the temperature to 125 F, so we’ll see if this solves the problem.

Other observations:

1. The manual has some text about replacing the cold water inlet with the anode rod, and putting the cold water inlet in the anode rod port. This was really unclear, and after messing with it for a while, my senses took hold and I realized there was absolutely no reason for this. When I asked tech support about this, they said sometimes the rod is in the hot water port, and interferes with installation. Something to keep in mind if you get one of these. I suggested they make this a bit more clear in the manual.
2. The manual states that you should replace the anode rod twice a year. I told them this was a pretty big operating cost, and maybe this should be stated up front. They told me this was a typo, and it should actually say “replaced every two years”. Much more acceptable.
3. Recovery rate is not nearly as fast as using the elements. Something to keep in mind.
4. You’re not supposed to keep the elements powered up, something about damaging the airtap. However, if there’s a high-demand period, they said you and unplug the airtap, and power up the elements, just not both at the same time.
5. I have a thermometer in the room with the airtap. When running, it does produce a pretty cold breeze, but it really doesn’t make much of a difference in ambient air temperature (which is about 68 F, by the way).
6. The unit is not set up to allow ducting of supply air. You can vent the exhaust, though. The exhaust vent is not a size to allow installation of a standard sized diffuser, so I’m going to have to fabricate something myself (since there’s no way I’m going to pay $78 for a $2 piece of plastic.
7. If you are bothered by noise, this might not be for you. It’s about as loud as a dehumidifier.
8. If you are looking at this to run double-duty as a dehumidifier, keep in mind that it doesn’t run based on ambient humidity. It’s a water heater. You will get supplemental dehumidification/air conditioning when it runs, though.

So far, I’m happy with it. I am actually amazed that this thing can heat the water so high. We’ll have to see how durable it is in the long run.

Good info Mike. Did you hookup your kill-a-watt meter to it yet?

So it sounds like this might be marginal (at best) for a family of three who all shower in the evening, is this a safe assumption? Add in a load of laundry or run the dish washer and I question if it would keep up. I know they are releasing a larger version soon (12k I believe???), although the price and performance are still unknown.

I'm beginning to think the best way to run one of these things (for me anyway) might be as a preheater for a second DHW tank. This way the AirTap would be doing the bulk of the heating, but the second tank down stream could heat any additional water as demand called for it. Example, have the cold water feeding into the AirTap equipped tank with a set point of say 125°+ F., then have it feeding into a second (smaller) DHW tank with a set point of say 115° F. Since the incoming delta into the second tank would be small, I cant imagine it would cost much in additional energy to use such a system and it would certainly have a high capacity if demand actually called for it. One down side to doing this is that you would have additional tank losses.

The other option might be to plumb it into a larger volume tank so there's enough warm water for at least two or three showers. Even though the recovery would take a long time, higher demand would likely be met. But again, there's the additional tank loss with the large volume of warm water.

At least with both of these scenarios people wouldn't end up with cold showers and the bulk of the water heating could still be done using this efficient device.

With this said, I have a 50 gal. (maybe it's a 53 gal.) electric water heater and a 80 gal. SuperStor hooked to my gas boiler (indirect) configured with a valve that allows me to use whichever I chose. I also have another 40 gal indirect tank kicking around. Both the 40 and 80 gal indirect tanks are not configured like a std. electric DHW heater in their layout. I think both have the water inlet at the bottom and the outlet at the top. Could the Airtap be hooked up to one of these tanks (I don't know how the system is plumbed into a traditional electric DHW tank)? If so, what I'm thinking is I installing the 40 indirect tank on the gas boiler and installing an AirTap unit on the 80 gal indirect tank. If the AirTap on the 80 gal tank did not meet our demand needs, it could be hooked up to feed into either the 50 gal. electric tank or into the 40 gal indirect gas fired tank. Thoughts?

My other concern is dehumidification. I need to run a dehumidifier in the basement during the warmer months. Any feel for how much dehumidification you're getting out of this unit? I assume the condensate is dumped through a drain, correct? Do you think this unit would cover my needs if I was only collecting a couple of gallons a day through a traditional dehumidifier in the summer?

Thanks again for your work on this project Mike...

Don't have the kill-a-watt yet. Marginal? Not sure. I've only had it in service for a few days, and so far I'm pleased with it.
Here are my thoughts on the preheater idea: If you were to do this, what purpose would the second tank serve? You are still using resistence heating to keep that water hot during periods of non-use. During periods of heavy use, you'll just be pulling cold/cooler water straight through, and the elements aren't going to be able to keep up any better. Are you just running regular electric heater right now?

I think the larger tank options would be best. I'm thinking now maybe I should have gone with an 80-gallon tank, for the same reason as you: more storage. As far as the inlet being at the bottom, the thing mounts to the cold water inlet/hot outlet nipples to keep it in place, with adjustable rubber feet in the front for leveling. I'm sure you could rig something up to mount it to, though. It would still be attached to the hot side. You are actually replacing the 3/4" hot nipple with a new one included in the kit. The airtap heat exchanger is then fed into the hot port (it's a copper "coil" about 6' to 8' long). The thermostat bulb goes in there two. The hot water then exits out the back of this fitting through a tee.

I can't really say how much dehumidification you'll get, but if you're running your dehumidifier for two, two-hour periods each day, then this might do the trick. I would classify it as "supplemental", though. You'd probably see your full-time dehumidifier run less? Condensate flows by gravity through a tube to drain/sink/whatever.

I can't really say how this will work out in the long run as far as meeting our demands, but I'm convinced that it is going to save bucu bucks, so I'm determined to make it work. I feel that I might see the 40-gallon tank working fine simply by keeping the thermostat set to the higher temperature?

One more note: I wrote the company about the change in tax credits - they said if you buy a new tank or other equipment, that also counts toward the 30% tax credit, since the air tap is just one component of the hot water system. That will put me at about $300 back now.

In case anyone is still interested in this...

It's been a week since I installed the AirTap (still no kill-a-watt meter). I have turned the temperature setting up to its max (130 F). Here's the only drawback I have encountered so far.

Since the thermostat operates on a 15 degree temp differential, it is possible to not use any hot water all day and still get hot (but not 130 degree hot) water out of your tank. In other words, let's say the heat pump runs at 5 am, and is then off all day. I might come home at 6 PM to take a shower. Just as I step into the bathroom, the heatpump kicks on again, even though I have not started the hot water. This means that the water temperature has fallen throughout the day, and is now at approximately 115 F. My shower is still hot, just not as hot as it would have been with the elements keeping the temperature constant all day.

My recommendation with this thing is go with a larger tank (80-gallon) and store more hot water. I'll make due, I'm sure, but the 40-gallon tank I got will probably leave me in situations with cold water at some point.

I also was thinking that maybe placing an uninsulated tank just before the heat pump might provide some "preheating" using ambient air. If I have 48 F water coming into an uninsulated tank and I don't use a lot of water, it is possible that that tank could warm to close to the ambient temp. of 70 F prior to being heated to 130 F by the heat pump. Just a thought...

130 isn't really hot enough for us. Our oil boiler is set to 160, and even then we generally do showers with the tap on full hot. No tank or storage to speak of. I haven't read anything but page 5, so hopefully this wasn't addressed earlier.


edit: went back and read. I do like the sounds of this thing, but it seems like their marketing dept needs to do a bit of work on their website and documentation. I don't use electric hot water or even have a separate water heater from my furnace, but it seems pretty useful to those who do. Thanks for the detailed posts Mike.

160 will scald within seconds, so either:

your water has cooled a lot by the time it gets to the tap - possible but not likely

you are reading the temperature inside the boiler heat exchanger - this is effectively the temperature of the water that gets circulated around your forced hot water system. Your hot water supply gets heated to this temperature, then is mixed with cold using a thermostatic valve, usually on the side of the boiler to a safe temperature.

your thermometer is busted


I am going to bet that the second is the case - you may want to turn up the temperature on this valve, and measure the temperature coming out at the faucet - I bet you it's not 160....

I agree, 160 is scary hot. 130 is actually too hot, but I am banking on showering in the lower-range 115 (which is perfect).

160 will peel your skin off and then cook your muscles to the bone. Take some carrots, celery, onions and cabbage in there with you, too to make it a meal.

I would measure the temp at the tap to get a true temperature. If you have the hot tap full open without mixing any cold, I'll bet you're actually looking at 115 to 120.

Thank you for the update Mike. Very much looking forward to your Kill-a-watt readings when you get them. You might want to consider putting the Airtap on a timer and having it shut off from say 8PM until say 3 PM, this way it doesn't have a chance to completely reheat your tank after taking your evening shower (although still brings it up a bit should you need warm water), and then kicks on again before you come home to get your tank fully up to temp. You would save energy doing this as well since your tank losses during the night and most of the day would be less because the delta isn't as high. Obviously you would have to play around with the timing to work with your family's schedule, but it should solve your 115° water temp issues, plus save you some money in the long run.

Using two tanks would reduce the recovery time and increase the supply for more hot water on demand. Since the first tank (AirTap tank) would be feeding the second tank with hot water (until it's supply is slowly diminished), the second tank would not have to work nearly as hard to bring the water up to temp (if at all) and the recovery would be minimal unless you used a lot of hot water. In the rare event you started to deplete both tanks (very unlikely), the two would also recover much faster. Yes, you'd loose a little efficiency since you'd still be using a resistance heater in the chain and it would have to maintain the second tank temp due to tank loss (which isn't that great), but the delta would almost always be minimal, so it wouldn't be carrying much of the work load at all. Better yet, you could use two tanks, each equipped with an AirTap, but set the first at a lower temp (say 75°) to reduce tank losses, this would be more costly to initially set up, but it would be very cheap to use and would supply a lot of hot water with less tank losses.

I have both resistance and gas DHW systems in place, I'm choosing to use the electric tank now because I have some issues with my gas provider... I would prefer not to give them my money, even though it would be cheaper for me to heat the water with gas.

I like the idea of having a large storage tank, but the only real down side is the increased tank loss... which is why ideally two smaller tanks with staggered temps, both equipped with AirTaps, would be more ideal.

I don't know how well your preheating tank would work without some type of HX in/on it. It would take a long time for 40 something degree water to come up to ambient temp without some type of HX or heat sinks on the tank. Now if you could place it close to your wood stove, that might work well.


Please continue to keep us updated with your findings!


BTW, I have to agree with the guys KarriOn, it's very doubtful your DHW temp is 160°, that would cause instant burns. 140° is about the limit, and even that can burn you if you stay under the water for any period of time.

Haven't gotten to it yet, but I am going to wrap my 40-gallon tank with R-13 fiberglass insulation, and top that off with some "double bubble" foil insulation (I have lots of both insulation left over from working on the house). The only part of the tank that won't be covered is the bottom. That should help tremendouly with tank losses - this would apply to a larger tank, too. It's going to look like a component of the space shuttle when I'm done, but it should do the trick.

Thanks for the clarification. The 160 is on the adjuster for the HX, and I don't actually have a thermo that reads what the temp is. This temp very well may be only used for the radiators, and the DHW gets cooled thermostatically like you say. I do realize there's no way the water coming out of the tap is at 160.

I'm interested. I've been lurking until I actually had something to say.

I have a GSHP, woodstove in the basement, electrical resistance water heater in the basement, and need dehumidification in the summer and am dedicated to reducing our off-the-grid energy demands so this is all very interesting to me.

I guess a few questions/thoughts I have:

After reading the whole thread and from what I'd already planned I'm now considering going with solar preheat, AirTap primary heat, with a tankless unit after that for higher than normal loads and to avoid tepid water. I would probably also control time-enabling of the various components with my home automation system (x10). I'd rather not use the tankless unit, instead using the remaining resistance element in the tank the AirTap is installed in. I'd like to know more about why AirTap recommends against this. Its hard to imaging how an element separated from their high-side condenser line by a foot of water in the tank would cause problems.

I realize that this scenario is not ideal for dehumidification but that's not my primary goal. I'd take what I could get as far as dehumidification and use my current dehumidifier or GSHP to make up the difference.

Thanks Mike for keeping us posted, even the lurkers I really hope this works out well for you.

Oh, yeah, I'm also a fan of the FSM but never made the connection with your avatar.

I've installed both the Airgenerate unit and the Nyletherm.
Both have their pluses.
The Nyletherm is much more rugged, built in this country and will be re-usable if your tank fails, since it circulates water into the storage tank.
It requires 220VAC and is hard wired. Since we manufacture unpressurized tanks, we will hook it up to a larger solar tank.
I ran it with an 80 gallon tank and never ran out of hot water. That was with two people in the house. I suspect it might not keep up with a couple teenagers.

The Airgenerate is cheaper and is not as rugged. It is 110VAC and plugs in. The heat output is the same. Since it has a heat exchanger that has to be installed in the
tank, I suspect that is will be difficult to move to another tank. The heat exchanger seems fragile to me, although it went in the tank okay.
It is less expensive, but you get less for the money.

Both units have a COP of about 2. I usually run the Nyle in the summer only, since my basement is insulated with spray foam and it chills the floor too much.
The Airgenerate ran into January and frosted up. We shut it down and should turn it back on again.
Of course, this is Maine and both basements are quite small.
The Nyle lists for $1,000 and the Airgenerate is about $600. The Nyle unit is sometimes on sale or available as a refurb. (They had some control changes.)

BTW, most boilers have a mixing valve that would (usually) never allow you to run water over 120F out of the tap. Anything 130 or higher is going to be intolerable and dangerous.

Who???

As an update to this, I heard from Rob at NRT about their HPWH. Here is the response I received and there are more details on their website...

So, I was checking these out, and trying to determine if it would/could be useful to me or not.

Right now, I have an oil fired boiler that provides hot water via an indirect hot water tank (3 zones - 2 are heat exchangers for our air handlers for heat, the 3rd is the indirect hot water tank.) Once nice thing about the tank is that it is an extremely well-insulated Mega-Stor tank, and has great efficiency for these types of tanks.

Looking at the setup of the current tank, it has a cold water inlet at the bottom, a hot water outlet at the top, and the boiler in/out on the side for the indirect coil. I.E. it's not gonna be easy to hook one of these units up (I was checking out the Geyser unit, and even exchanged a few e-mails with them today.)

We currently have a 50 gallon tank and 2 teenagers. 'nuff said there about what happens with the hot water. ;-) We also have an 80 gallon jacuzzi tub which, of course, we can't fill without fully draining the tank. Based on this and other things, it's clear the builder of the house wasn't thinking clearly.

Anyway, what I was thinking, is that I could possibly kill 2 birds with 1 stone here.

(1) Install second hot water tank (30-40 gallon.) Make this one electric, and install it before the existing indirect hot water tank, so that the outlet from the new tank goes to the inlet of the existing tank.
(2) Install the heat pump on the electric tank.

In theory, this should give us two benefits - a larger reservoir of hot water, and most of that hot water will be heated by the heat pump. The oil burner should only run to provide hot water when the heat of the indirect tank drops below temp, either due to being exhausted, or because the tank has been idle enough that it cooled down.

There is also a third benefit - I usually have to run a dehumidifier in the basement most of the time during the spring/summer/fall. This hot water heat pump also acts as a dehumidifier. So, in actuality, I wind up killing 3 birds with 1 stone.

I know these heat pumps are quite expensive - the Geyser is $1,199! Plus a new tank, plumbing, wiring, I'm looking at ~2K or so when all is said and done. But, I'll be burning a lot less oil (but probably have a higher electric bill - we'll have to see what the offset is.)

So, opinions?

My first take is that it will really depend on your electric rates and how bad the humidity is in your basement in the summer.

With oil at $4/gallon the previous winter, I did a back of the envelope calculation that showed that electric water heat at ~12 cents a kilowatt hour was competitive with oil. I heat my water with off-peak electricity at ~10 cents/kWh, and I was curious.

Here is the math:
3414 BTUs/kWh
140,000 BTUs/gallon of oil

Electric water heat = (3414 BTUs/kWh)/($0.10/kWh) = 34,140 BTUs/dollar (assuming 100% efficiency and ignoring tank losses)
Oil Heat = [(140,000 BTUs/gallon)/($4/gallon)]*65% efficiency = ~22,500 BTUs/dollar

So with oil at $3/gallon, it's probably the same. At $2/gallon, oil is cheaper.

BUT, with the heat pump water heater, the coefficient of performance is ~2, so the cost per BTU is halved, or the BTUs/$ = 68,000. Thus, it is competitive with oil at $1.50/gal. We probably won't see that for a while.

Whether it makes sense economically is dependent on how much water you use in a year. Before I invested in this, I would make sure that there were water saving fixtures on the showers. A front loader washer may be a good investment also, depending on how many loads of warm or hot laundry you do in a week.

One thing I haven't taken into consideration is the fact that oil burners are usually a lot more inefficient in making hot water during the summer when they are not also used for heating. This tilts it further to a replacement with the heat pump. Also, the dehumidification is a nice side benefit, and another money saver if you run a dehumidifier in the basement anyways.

If you were to do it, I would go with an 80 gallon electric tank as a pre-heater, and maybe even get ride of the oil tank completely.

I read a great article about someone who put a 20 gallon hot water tank feeding the bathroom that his teenagers used so that there was essentially a hard stop to the amount of water they would use. I would definitely do that if I had teenagers. I don't recall going through a tank of hot water when I showered as a kid.

Thanks for the reply.

Right now, in my area, it's ~$0.18/kWh for electricity (no such thing as "off-peak" on my bill ;-( ) and oil is $2.29/gallon.

We already have the front loader washing machine, shower saving devices in the showers, etc.

It's not a huge issue - one of the biggest complaints is that two people cannot take a shower at the same time without one of them running out of hot water (kids upstairs, us downstairs.)

Also, our boiler is listed as 86.2% efficient.

So, it is sounding like, economically, we are better off with the oil boiler right now.

The one thing that comes into play is the dehumidifier. We must run it a whole lot, so that is like wasted hot water we could, in theory, be getting back...

But, on the flip side, I would like to reduce my reliance on heating oil, and do my part for the environment - the more green electricity I can use instead of oil, the better I feel.

I was looking at the wood boilers, but those are outrageously priced, and you still have to feed 'em wood which costs. They are nowhere near economical, at least not right now. Maybe if oil hits $10/gallon, but if that happens, I expect wood prices to skyrocket as well.