A new way to get hot water

woodgeek Posted By woodgeek, Apr 12, 2012 at 10:06 PM

  1. woodgeek

    Minister of Fire

    Jan 27, 2008
    SE PA
    Got my heat pump water heater installed today...an AO Smith 80 gallon unit.

    Is 7' tall and weighs 1000 lbs. I will give a report in a few days....in the meantime my
    oil boiler is shut down and disconnected, yay.

    I just found lab test report on this unit from NREL .... see attached. They like.

    Attached Files:

  2. semipro

    Minister of Fire

    Jan 12, 2009
    SW Virginia
    I like our GeoSpring HP water heater. Its worked flawlessly since we got it 15 months ago and decreased our electricity usage.
    I keep trying to think of ways to get waste heat from devices in our house down to the room where it live (fridge, electronics, etc.).
  3. DickRussell

    Burning Hunk

    Mar 1, 2011
    central NH
    There is a good discussion of air-based heat pump water heaters going on here:
    These devices aren't necessarily right for every house. It depends strongly on climate where the house is, where the HPWH is installed in the house, and how the house is heated. Particularly for climate zones 5 and higher, a HPWH is not a great idea, as the heat put into the hot water tank is partly the electricity used by the compressor and partly heat from the surrounding space, providing in effect air conditioning (cooling) for that space. If the heat removed from the air must be made up by the heating system, then the cost of heating the hot water is partly the cost of electricity and partly the cost of fuel for heating the house. In summer, at times when A/C is needed for cooling, then a HPWH has an obvious benefit.
  4. begreen

    Staff Member

    Nov 18, 2005
    South Puget Sound, WA
    We've had a couple threads on them here too. My main concern is longevity. When they are working they seem fine, but their track record is mixed. The worst are the type that have weak compressors or anode rods that can't be replaced. The other complaint I have read about is that some can be noisy. How is the AO Smith unit for noise?

    Here is a long discussion thread on the topic by folks that own them:

  5. woodgeek

    Minister of Fire

    Jan 27, 2008
    SE PA
    Both of those links make a lot of sense and jibe with my understanding (unlike a couple crazy-anti screeds you can also find on the internet). My case is pretty ideal....my climate is heating dominated, but mild, and I have an attached unconditioned two car garage (tucked under) that runs 40-80°F year round, and requires some dehumidification in the summer months. It might have to switch to coils a little in the dead of winter (the Smith has a lower T cutoff at 45°F), but I still expect to get a SCOP > 2.

    RE the noise, the compressor itself sounds a lot like my grandma's frigidaire when I was a kid (if you know what I mean), but the fan on it is 400 cfm, and sounds like and feels like a 400 cfm fan. Not unlike a 'maximally large' window unit AC on high overall.

    As for longevity....I have also read the reports on the GE geospring. I can only assume that a bad lot or two got past quality control, since there seemed to be a big flurry of 'lemons' well after launch, along with plenty of folks with no problems on similar time spans. I have not heard anything comparable on the Smiths, and they seem to have launched a couple years ago. I don't see anything deeply unreliable about the technology, mechanically the same as a 5000 BTU A/C unit.

    For those who are interested I found some great lab reports on these units (I posted a short one above, but the full report was too big to post. You can find it by searching the net for: "HPWH_Lab_Evaluation_Final_Report_20111109.pdf"

    The full report compares all the existing models....basically the Geospring, the Rheem unit and the Smith. It finds that all the units met or exceeded their stated specs, but showed significant performance differences between them based on their engineering (as well as their size). Looks like the Rheem units are the worst COP performers due to their choice of refrigerant. They said that the geospring underperformed partially because of its control logic that kicked on recovery too late, pulling down the FHR. And they thought the Smith was the best choice for high usage households due to better control logic (as well as 80 gallon size, the Smith also comes in a 60).

    They also did some fairly careful simulations of real world performance in different climate zones and installation configurations (basement/garage/attic)

    Overall I found the report to be way more informative than all the other info I found on the net put together.
  6. Seasoned Oak

    Seasoned Oak
    Minister of Fire

    Oct 17, 2008
    Eastern Central PA
    in summer you can benefit from the cool"waste" air coming off the coils.
  7. sloeffle

    Feeling the Heat

    Mar 1, 2012
    Morrow County, Ohio
    I looked into a heat pump water heater when I put new mechanicals ( geothermal furnace, hot water heater ) into my house when we added a basement. I am in climate zone 5 also. The main reason that I did not got with the HP water heater is that it is made out of steel. I have a hard time spending $1200 - $1500 on a water heater that is going to rust out in 10 years. Just to break even, you end up having to save at least 120$ a year. From the greenbuildingadvisor article, the average user saves around 40$ - 250$ a year. If you are on the low end of the savings spectrum your investment never pays off.

    Rheem Marathon has been building hot water tanks out of fiberglass for years. If they built a HP hot water heater out of fiberglass then I think they would have something that I would buy. I bought a Marathon just for this reason. Buy it once and be done with it.

  8. woodgeek

    Minister of Fire

    Jan 27, 2008
    SE PA
    I liked the marathons, and would have gotten one if I had gone conventional. Crunching the numbers, though, I am saving >$300/yr compared to conventional electric, for about $1500 additional cost.

    Edit: after utility rebate, the Smith was ~$1200 more than a Marathon, and my projected savings are ~$250/yr. Of course, I am saving $900/yr relative to my oil boiler, but I would have saved $650/yr with a marathon for lower up front.
  9. benking


    Oct 19, 2007
    Portland, Maine
    I recently installed an 80 gallon Stiebel Eltron Accelera 300. I too have shut down the oil boiler for good (with the exception of vacations in the winter). I haven't received an electric bill yet but the reading on my new smart meter indicates my usuage will be just a few KWH above the same time last year. I will report more when I get some bills. So far tons of hot water, its in the basement and the noise is easy to overlook, less noise than the old boiler firing up but it runs for more extended periods of time. I have the electric element assist nearly off and we have had no signs of luke warm water. With this unit I understand that as long as the basement stays above 41 deg it will continue to use the Heat Pump. Very cool tech, 10 year warranty, payoff calculated to be 3 or 4 years. So far so good.

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