Heat Pump Hot Water Heater Recommendations?

[jeffesonm]

I am currently heating DHW with a coil in a 1957 oil furnace that used ~150 gallons over the past 6 summer months, or about .83 gallons/day @ $3.59/gallon = $3/day = $90/month. In the winter I used just a tiny bit more as the wood stove provides nearly all the heat. I've only lived here a year and knew this was an inefficient way to heat water, but now that I'm doing the math, it's looking downright awful.

Based on all the info in this thread, I should look into a separate hot water heater. It's only me and the missus and we're pretty frugal in our hot water usage. Just upgraded from an insert to a freestanding stove so I hope to heat exclusively with wood this year. No natural gas here, and I plan to do a gasifier setup in the next 3-5 years as part of a more major house renovation.

I can get a $500 rebate from my utility company for a heat pump water heater and was scoping out the GE GeoSpring, currently on sale for $999. With a %10 off coupon at Lowes and the $500 rebate, it sounds about equal price wise with a regular electric unit. I read some old threads and it sounds like the few that have this HWH have been happy.

Any other recommendations?

 

[woodgeek]

For the two of you, the geospring will be a great fit, and as you said the price is right. You can figure that your DHW costs will be <$15/mo, and the unit will save you >$700/yr, which is a pretty decent ROI.

The considerations are:
1) Size....recovery is slower in HP mode, if you got one that was too small, you might set it to run hybrid mode (rather than HP only mode) cutting into your savings. In my family of 4, with two soon to be teenage girls, I got an 80 gallon unit (from AO Smith), 50 gallons should be ample in your case.
2) Noise...all the units make a bit of fan noise, more than a fridge, more like an AC unit. Locate the unit somewhere where it can breathe conditioned air, but the noise will not be an annoyance issue.
3) Heat stealing....in the winter it will pull a (pretty small) amount of heat from the conditioned space. Folks on the intertubes make a BIG deal about this and say to never get a HPWH unless you live in Florida, but they are nuts. The way it pencils out is that it is a non-issue unless your heating season is long and your space heat BTUs cost as much as electric baseboard heat....then the HPWH has the same operating cost as conventional electric DHW. In our climate, with wood heat this is a total non issue.

If you have a location for it in your house, and rebates in place....its free money.

 

[woodgeek]

Of course, your particular savings assume that you can shut down the oil boiler COLD when you are not using it. Have you down that without issues?

 

[jeffesonm]

I planned on putting it in my unconditioned basement... it's about 1000 sq ft, entirely open, uninsulated, but 80% of it is underground so the temps stay pretty stable even in the winter. I run a dehumidifier in the summer so hoping to ditch that.

As for the oil boiler, I've read you can have problems when you shut down an old boiler, so that worries me a little. Aside from backup when we're on vacation, I won't really need it, and don't see any other choice, so I'll just cross my fingers and hope for the best.

 

[woodgeek]

Since most of your oil usage is standby, if you keep it hot it will still cost you nearly the same amount every year whether you get a new DHW system or not. If you reduce the boiler temps a lot to reduce standby (I tried that) you can get condensation and a lot more sooting/plugging/CO. That said, most boilers DON'T leak when you shut them down, and IMHO, if it doesn't leak on day one, it is unlikely to start dripping later. More to the point, I think we are talking a drip, not a flood, but I would shut off the makeup water supply when it was not in use to be safe).

You could shut it down over night for a test. If you do have a leaker, then it is a $1000/yr monkey on your back, and you might want to consider some long term path to ditch it, which may involve a HPWH, or not.

 

[jeffesonm]

I will find out when I get the new hot water heater... maybe the heat pump will dehumidify enough to make up for the leaky boiler

Long term I'd like to get a gasifier with storage for heat/DHW in the winter. In the summer I will likely use HPWH for DHW. I'll need something for heat backup but haven't yet decided what that should be. No natural gas here, but about to put in a propane tank for cooking.

 

[DBoon]

Hi jeffesonm, I added a Geyser HPWH to my electric storage tank. There is only my wife and I at our house. We went from 200kWh/mo or so of usage to 100kWh/mo or so of usage - about 50% savings (<100 kWh in the peak summer months when the incoming water and basement is warmer). You'll find postings from me in the green room on this topic.

Here in Central NY, it will cool down my well-insulated basement too much in the winter, even if I run the oil boiler now and again (and throw off some waste heat) that it makes sense to just heat with electric resistance from December through March. Maybe Central NJ will be different, but if you cool your basement down to near 50 degrees in the winter (not hard by the 2nd year of running it, when you live in a cold climate), then you need to go electric resistance.

You'll get the best efficiency with 120 degree water setting - go higher than that and the efficiency drops off pretty fast.

I mostly don't have to run my dehumidifier in the summer anymore. Maybe two of the most humid weeks of the year. Otherwise, the HPWH keeps the basement pretty dry.

 

[STIHLY DAN]

Plus the $300 gov rebate. Also a mixing valve works great. I do not believe the lower temp greater efficiency. Set at 140, use mixing valve to 128. You will use less hot water.

 

[woodgeek]

Its not lower temp = greater eff, it is lower temp = lower standby. And in DHW-only apps with a tankless coil, that standby can be >80% usage. Do you believe that?

 

[georgepds]

IMO.. don't bother with the heat pump water heater.. the COP on a water heater is ~2. This compares poorly to the 3 to 8 COP from an air to air heat pump. You just will not save that much energy, and you have a much more complicated system ( compressor pump and heat exchanger, as opposed to a simple electric resistance coil). The reason for the poor performance on water heaters is that hot water is, well, hot.

The Carnot efficiency ( the best you can do) is
Hot temp/ ( hot temp- cold temp)
where temperature is absolute temp.. You can see the efficiency grows tremendously when the hot temp approaches the cold temp.. which it does for air conditioning.. but not so much for water heating

 

[woodgeek]

Maybe with cheap low-C electricity like you have I could go for that, but if the kWh are expensive and C-intensive, then I think the savings pencil out a decent savings. And if the compressor goes, the coil picks up the slack indefinitely.

And neither ASHP nor HPWH in the current generation approach the Carnot eff, which is more like 8 for the ASHP and 4 for the HPWH. Lots of room for future innovation.

 

[BoilerMan]

For 365 bucks my Nyletherm1 has surpassed my expectations by a mile! American made, and costs $15-20 to operate in our house of 3, and we take long showers. Ore electric rate is 15cents/kWh. No way oil can touch that price, unless we were back in the < $1/gal days.

TS

 

[DBoon]

I do not believe the lower temp greater efficiency. Set at 140, use mixing valve to 128. You will use less hot water.

It's ok if you don't want to believe it, but that is the reality. Efficiency drops off after 120 degrees - I've metered it and seen it.
You will use less hot water if the water is hotter, but you will not save energy in doing so since you will use more kWh to generate the same BTUs.

 

[jeffesonm]

In what was my first ever plumbing project, I installed the Geospring last night. I am pretty happy with myself... 30 some sweat connections and the only thing that leaked was a damn threaded connection... not enough tape. After a big of cursing I got that squared away and the heat pump is churning away down there. Still need to adjust the mixing valve so the water is a little hotter at the faucets. I also need to determine if the water near the now-cold boiler is actually a leak, or just leftover from the mess I made yesterday draining and refilling the DHW system.

 

[AK13]

Good call on the Geospring. I think you made a good decision. My co-worker just installed them. There are better units available but I think that the GE you bought is the best value as long as you can live with the 50 gallon tank.

Nice install! A lesser man would have just strung up a bunch of pex spaghetti.

 

[STIHLY DAN]

Nice install. Are you far enough away from that wall? I think the outlet of the fan needs 9-11 inches clearance. Did you get the built in checks on the mixing valve? Also, I listened to what DBOON had to say. I adjusted the temp to 130 on the heater, still using the mixing valve and have not noticed a difference in water temp. So I must be saving something more.

 

[jeffesonm]

Hard to tell from the photo but yes it's just over a foot from the wall. The mixing valve does have a check valve built in. Maybe I will try lowering the heater to 130... it's just the missus and I and we use very little hot water, so I don't think I'll miss the extra capacity.

Also on a side note I really enjoyed sweating pipes... looking forward to doing a gasifier install one day.

 

[BoilerMan]

Hard to tell from the photo but yes it's just over a foot from the wall. The mixing valve does have a check valve built in. Maybe I will try lowering the heater to 130... it's just the missus and I and we use very little hot water, so I don't think I'll miss the extra capacity.

Also on a side note I really enjoyed sweating pipes... looking forward to doing a gasifier install one day.

Copper work is one of my favorite pastimes. Last I counted I was approaching 500 sweat joints for the heating system. I always test any copper circuit I can with air, much easier to fix a leak before there is any water in there!

TS

 

[maple1]

For 365 bucks my Nyletherm1 has surpassed my expectations by a mile! American made, and costs $15-20 to operate in our house of 3, and we take long showers. Ore electric rate is 15cents/kWh. No way oil can touch that price, unless we were back in the < $1/gal days.

TS

Hey TS - did you plumb your Nyle right to your DHW water? I still have a HPWH bouncing around in my head for our place, but was thinking if I got one I might plumb it to my boiler/storage water so it pumps through my DHW HX, and can heat my DHW and put some meat into my storage tanks. Aw crap, second thought I guess never mind - just realized you don't have storage. But third thought, since you've had the Nyle for a while - if you had storage would you bother trying to get any heat into storage, or just stick to heating your DHW tank?

 

[BoilerMan]

I would not consider piping it into your storage, unless you have a lot of humidity you want to get rid of, or you want some A/C. I duct mine into our bedroom and bath (about 300 square feet total) and run it on a timer so it only runs at night for A/C while we sleep. It's rated at 6000 btu/hr which I think is a bit optimistic. If let run strictly off the aquastat on the water tank it runs around 7 hours every 28 hours or so, mind you I take two showers in the summer after a long hot day of working outside.

You are correct that I do not have conventional storage, just the masses of concrete. I contemplated fabbing up a water to water heat pump and cooling the slab and dumping the heat into the DHW tank, but we don't really have cooling needs, the slab is cool as it is. Poor COP.

I think having some essentially free A/C in the summer, and wood in the winter for DHW is the best of both worlds. You can just connect it with you electric tank and if it can't keep up the elements come on line.

TS

 

[Seasoned Oak]

It's ok if you don't want to believe it, but that is the reality. Efficiency drops off after 120 degrees - I've metered it and seen it.
You will use less hot water if the water is hotter, but you will not save energy in doing so since you will use more kWh to generate the same BTUs.

Exactly .You can save a bundle just by turning your regular electric DHW heater down. I have mine where i rarely need to add cold water for a shower with it and I barely notice it on my electric bill.
You have to be careful if your on a well but for city water, no problem. If it turn it up hot, my bill jumps a lot.

 

[iceguy4]

IMO.. don't bother with the heat pump water heater.. the COP on a water heater is ~2. This compares poorly to the 3 to 8 COP from an air to air heat pump. You just will not save that much energy, and you have a much more complicated system ( compressor pump and heat exchanger, as opposed to a simple electric resistance coil). The reason for the poor performance on water heaters is that hot water is, well, hot.

The Carnot efficiency ( the best you can do) is
Hot temp/ ( hot temp- cold temp)
where temperature is absolute temp.. You can see the efficiency grows tremendously when the hot temp approaches the cold temp.. which it does for air conditioning.. but not so much for water heating

I read your post and I don't fully understand . I have a 60 gal AO Smith HP heater that I use in the summer only. I had an electric 40 gallon that craped out (also used during summer only.winter ...zoned boiler mate).I LOVE it. Cant notice it on my electric bill...A bonus...no more de-humidifier( a "complicated system" eliminated)...0nly downfalls I see price,(if you can own one for under $500, not a factor) size...(big...tall) noise (same as dehumidifier)

You just will not save that much energy

for my application this is NOT true