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Community and Q&A

Using a Heat Pump Water Heater to Dehumidify a Basement

richmass62 | Posted in Energy Efficiency and Durability on

Currently I am running a dehumidifier about half of the year in my basement, along with an electric water heater. I am currently considering a switch to a heat pump water heater. The GE model, for example, is under $1000, so this is an investment that could pay for itself by taking $150 to $200 a year off our electric bill.

I am wondering how much dehumidification I can expect with the various products now out there — the Rheem, Geyser-R, GE, AO Smith. What is the experience of those who have installed these models?

I am in a cold climate, so I will install the heater in the colder part of the basement and increase the ceiling insulation there.

(I might even set it up so that I can choose which part of the basement the unit will vent to based on the season.)

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  1. GBA Editor
    Martin Holladay | | #1

    I hope some readers who own these appliances will be able to respond.

    If you install the heater in the coldest part of the basement, it will not operate as efficiently as it would if it were located in a hot location.

  2. richmass62 | | #2

    I am also looking for real world info on how these units perform in colder temps. I assume that different units have different performance curves based on both the ambient temperature and the humidity... are we talking about a 5% performance hit, or a 25% hit? The actual numbers would be good to have and it would be great to be see if some units operate better in cold temps than others.

    If the unit won't work well in the basement than there are some outdoor options:

    EcoDAN (marketed to UK and Australia)
    EcoCute (market to Japan)

    Thanks for responding Martin. I think I will PM a couple of people on this site who reported installing these units last year.

  3. user-626934 | | #3


    I have a heat pump water heater in conditioned space, and I'm in a mixed/humid climate (Charlottesville, VA), but I can answer some of your questions.

    1) The amount of dehumidification depends on the amount of moisture in the air in your basement. The more moisture you have, the greater the latent (moisture) heat removal will be and the lower the sensible heat removal will be. Unfortunately, the manufacturers typically offer very little in terms of expanded performance specs for various dry bulb and wet bulb temperatures.

    2) The dehumidification is out of your control. You’ll only get dehumidification in proportion with the volume of hot water you use. It might not be enough for your needs.

    3) The manufacturer’s specs that I’ve seen typically show a low end operating temperature of about 40F. This is probably due to the potential for frost to form on the coil at lower temperatures.

    4) All of the integrated units on the market have various operating settings. Typically there is a “heat pump only mode”, a “hybrid” mode where the heat pump is augmented by the electric resistance heater, and a “high demand” mode where the heat pump is turned off. 

    5) I would install the water heater in the warmer part of the basement. I also wouldn’t increase the ceiling insulation just because of the water heater. 

    6) If electric water heating is the only reasonable option, an integrated heat pump water heater is a no brainer for most climates.

    7) Also to remember - they are a little bit noisy (50-60db) and their recovery time is slow when in “heat pump only” mode.

  4. wjrobinson | | #4

    These things are absolutely not for heating dominated climates. End of story.

    They absolutely ARE perfect for cooling dominated climates like Puerto Rico.

  5. richmass62 | | #5

    I haven't completely given up... AJ, I believe you have been saying good things about the Daikin AC Altherma... a unit with the compressor outdoors.

    There is also another outdoor cold weather heat pump product on the US market, the north american office is now in Toronto. This is the Aermec ANK Reversible Heat Pump ( Looking at their spec sheet, I see the following for their SMALLEST system:

    heating capacity: 37K btu
    input power: 3.12 Kwh
    water flow rate: 8.36GPM
    COP: 3.12

    The problem with this as far as I see, is that the temp of the processed water for this spec is only 45 °C / 113 ºF. For the Daikin, the maximum temp is 131 F (55 C).

    I can't tell what the maximum temp is for Aermec; I believe they are assuming the supply water will be 7 degrees C, or 45F.

    As I mentioned in another thread, we would do well with a small system as we are only providing supplemental heating (we have a relatively new gas-fired furnace). Although a larger system, if not too expensive, would allow us to change the configuration and draw more on electric heat if gas prices spike.

    I can't find any posts discussing the AIRMEC on this site, does anyone have any experience with it?

  6. richmass62 | | #6

    I just found out that a friend of a friend installed one of the new heat pump water heaters, probably the GE, in her basement here in cold climate Massachusetts. Of course, it matters where in MA you are, as an urban location with 2 deckers spaced 10 feet from one another will have much warmer ground temps than a rural location where the homes are isolated from one another. So I will try to find out from her how the water heater is performing.

    According to a 3rd party testing report:

    the GE water heater performs much as advertised. However if the space where it is installed drops below 45 degrees F it will switch to electric resistance mode. In my location the basement currently drops below 45 for about one month, however the insulation I am putting outside the walls is very likely to increase the basement temperature so it will seldom drop below 50. 45 degrees is below ground temperature and is due to an excess of exposed fieldstone.

    Based on the testing results I linked earlier, I would expect the water heater to drop the basement temp by up to 2 or 3 degrees after a very high use period (i.e. several showers in a row). However I would also expect the basement temp to recover within a hour because of the large amt. of exposed stone. I am guessing that the efficiency rating would be close to 2.2 in the summer and would drop down as low at 1.7 in the winter.

    This is still a lot better than the efficiency I am now getting year round, which is under 1.0.

  7. wjrobinson | | #7

    Rich, if I put something in my basement that removed heat from my basement, it would drop my basement to below freezing. As it is it can drop to below 40. Now putting a pellet stove near a HPWH in my basement would work.

  8. richmass62 | | #8

    AJ, it sounds like your basement is influenced by outside air temperatures, as mine is. But I don't know... how much of your basement consists of uninsulated walls that are above grade to 2 feet below grade?

    In my case the basement has 6 foot high walls, and 129 linear feet of outside wall. That is a total of 734 square feet of outside wall. The wall has 6 sections. A little math to figure out the square footage that is going to be continually exposed to freezing (frost depth is 4 feet but I assume it only reaches that in extreme years; only top 2 ft will stay frozen for the entire month of january):

    25 ft - 1ft exposed to air, 3 ft freezing temps, 75 sq. ft.
    20 ft - 2 ft exposed to air, 4 ft freezing temp, 80 sq. ft
    6 ft - 2 ft exposed to air, 4 ft. freezing temp, 24 sq. ft
    14ft - 2.5ft exposed to air, 4.5ft freezing temp, 64 sq. ft.
    30 ft - 4 ft exposed to air, 6 ft. freezing temp, 180 sq. ft
    34 ft - 3ft exposed to air, 5 ft freezing temp, 170 sq feet

    so 593 sq. feet of the wall will be regularly exposed to 32 degrees. That is 80.1% of the wall! If I add insulation and bury more of the walls underground (the latter is needed for structural integrity of the building) then the basement is not gonna be nearly as cold!

  9. wjrobinson | | #9

    Rich. This is how I see your quest. You have decided that your cellar has excess heat that you can tap to heat your water. I see anyone doing so in our climate as absolutely delusional. Not saying I don't like you and your quest, I do. It's just not on my list of worthy experiments.

    Since you are intent upon doing so... Do so. Then let us know how all turns out. I love to see people experiment.

    My research into ground temps hear show 40s at best in winter.

    I feel superinsulation, and buildings with inner shells that are insulated are far more productive pursuits. And there are many other ways to heat a home and or domestic water.

    I just saw an ad for a 93% efficient pellet stove.... Great source of heat for me when temps fall below freezing.

  10. richmass62 | | #10

    AJ --
    I did add lots of exterior insulation myself when the ground thawed around December 17. So the north and south walls are covered with 2 or 3" of EPS, going below grade around 12 to 18". Couldn't go down 24" as originally planned due to a concrete ledge! I also hired a mason to do some prep work that included injecting mortar and concrete into voids and hollow areas. Still have to cover the very-exposed east wall, though.

    The results are significant... minimum temp was 40 degrees last year. This year it has been no lower than 46 degrees F. I am pretty sure that I can get it close to 50F once the east wall is done.

    As far as actual performance of a heat pump water heater in cold conditions, I found an interesting detailed post on another site, where the poster received detailed answers from GE:


    Q: I live in eastern Iowa (about three hours directly west of Chicago). It gets really cold here in the winters, as you can probably imagine. While I know that the GE Hybrid Water Heater will be much more efficient in the warmer months for me, I'm still concerned about the winter. The ambient air temperature in my basement this morning was in the upper 40s, possibly as high as 51 degrees (depending on which thermometer I was using). According to GE, the heat pump component of this water heater will work down to 45 degrees. But, I'm assuming that there is a rate of diminishing returns here, correct? Or am I not understanding how the technology works?

    GE: You are correct. The heat pump will operate down to 45F. Below 45F, the unit uses electric resistance heat elements, and the efficiency is similar to a st andard electric water heater. Above 45F , the heat pump efficiency is related to the ambient temperature. But, even at colder ambients (45-60F), the efficiency is still much better than running in standard electric mode.

    Q: If my basement were to get cold enough that this water heater had to work in Standard Electric Mode, can you tell me how efficient this water heater is in this mode? In other words, a highly efficient traditional electric water heater might have an Energy Factor of .94 or .95. How does this unit compare if operating purely in standard electric mode?

    GE: A standard electric water heater typically has an EF in the 0.88-0.90 range. The GE Hybrid water heater has an efficiency of 0.89 when running in standard electric mode. Therefore, when running in standard electric mode, the unit has an efficiency just like a standard electric water heater. As you state above, some higher efficiency electric water heaters can achieve EFs of 0.92-0.95, but these units tend to be more expensive than standard electric water heaters without providing a significant increase in efficiency.

    Q: When the Energy Factor of 2.35 was calculated, what temperature ranges were used for that calculation? Given my winter basement temperatures, I'm guessing that the Energy Factor in my situation will be significantly lower, correct?

    GE: Official EF testing is based on the Department of Energy test procedure and is run at 68F ambient temperature. As ambient increases, EF increases, and as ambient decreases, EF decreases . Based on our internal testing at GE, the GE Hybrid water heater's EF ranges from approximately 1.8 at 45F to 3.2 at 120F. A 1.8 EF means that the unit is up to 50% more efficient than a standard electric water heater. A 3.2 EF would be up to 72% more efficient than a standard electric water heater. These are NOT published values, but are provided for guidance only.

    Q: Finally, with a winter basement temperature in the upper 40s to lower 50s, can GE provide an estimate of how efficient this unit might be during the winter months?

    GE: Using the info provided in the above answer, the EF of the GE Hybrid water heater will be approximately 1.8-2.0 when ambient temps are in the upper 40s to low 50s. Therefore, at these ambient temperatures and EFs, the unit should operate between 50-55% more efficiently than a standard electric water heater that has an EF of 0.9.


    The main reason why I haven't bought one of these units so far is that they are new and not as reliable as they could be. It might be worth waiting for the "Geospring 2" model to come out, as the original units had some issues with the coils failing, needing replacement after 1 year. From what I understand, three new manufacturing plants are coming online in the US in 2012, in Louisville, KY, Bloomington, Indiana, and Decatur, Alabama and the new water heater is viewed by GE as their main product:

    AJ -- your location might be colder than me. You said you were in zone 6a. With the new USDA map released last week...

    ... I have been bumped to a warmer climate zone!


  11. wjrobinson | | #11

    Rich, keep up the good work. Just keep the Kool Aid.

    Heat pumps transfer heat from a to b. I only have 8 weeks a year when I would benefit from stealing my homes heat to heat my homes water. End of story for me.

    If I lived in Key West, It would make sense.

    Natural gas and pellet stoves and passive house are my rural cold region choices.

    Like Martin said, we need owners of these water heaters to post here to discuss this with you.

  12. user-659915 | | #12

    Rich, what I get from your original post is that whatever the performance benefits (or not) may come from the water heating aspect of the HPWW, you are expecting significant savings in your dehumidification costs, and perhaps you also hope this will compensate for the known disbenefits of HPWH in heating climates such as have been emphatically pointed out by AJ. I think this is unlikely to be the case and I would refer you back to post # 3 by John Semmelhack which offers a lot of good sense and particularly points out that any dehumidification provided by the HPWH is incidental and beyond your control. My own semi-educated guess is that your $150 - $200 a year in projected savings would be wildly optimistic.

    I'd also question why your dehumidifier is costing that much to run. Here in North Carolina I can operate my whole-house a/c system through a long, very humid summer for less than that. I'll confess I have no experience of the particular conditions in your part of the country but perhaps you should spend a little money on upgrading the air-sealing of the enclosure rather than continuing to bail what appears to be a rather leaky boat.

  13. richmass62 | | #13

    AJ -- we won't be robbing heat from the house if we insulate the basement ceiling. now there are 3 full inches of wood flooring layers on the 1st floor and no insulation.

    James -- the heat pump water heater is just one option. The other option is solar thermal -- which has fantastic rebates just in MA.

    And we are updating the thermal envelope... see my other threads on that!


  14. hotwaterbob | | #14

    Hi Rich
    I live in Maine and have had a Geyser hot water heat pump for 11 years and here is what I do know.

    -My Geyser is connected to my 80 gallon hot water storage tank with t valves and the Geyser has an aquastat to determine when it needs to come on. I turn the unit on and switch the valves after I get my FHW furnace cleaned in the beginning of May each year and run it until I need to turn the furnace on for heat. When the furnace is used for heating, my hot water is set up just like another zone so the incremental cost for winter hot water doesn't seem so bad. Also in the winter, the air is dry in the basement and unless I keep the heat up, the efficiency is pretty low so I just turn it off for the 6-7 months when the heat is likely to be on. Also when the air is really dry, it sometimes freezes up and has to go through a thaw cycle that just doesn't seem very efficient to me.

    -It takes about 12 hours to recover 60-80 gallons of hot water so my Geyser is running at least half of every day and giving me free de-humidification in a 1000 square foot basement (partially finished). My basement is bone dry and about 65 degrees all summer. You can see in the picture that I duct the majority of the cool dry air into my finished portion of the basement. I do have a de-humidifier on a WEMO switch that is set to run each morning from 6-9 when the Geyser is not likely to be running and when we are away and not making any hot water, I set up rules so that it runs about 12 hours a day.

    -If we have a lot of company, I sometimes switch it back to the furnace as the recovery is much quicker but it kills me to do that in the summer.

    -I paid $1100 for my Geyser and got back State and Federal rebates that totaled about $600 back in 2010. We used to use about 250 gallons of oil to heat hot water in the summer (May to October when the furnace was not needed for heat) and in 2010 I was paying $3.00 or so a gallon for oil so I broke even and then some in the first season I used it and have probably saved 2500 gallons of heating oil since (approximately $7500!)

    -Do it. I'm thrilled with this and only wish I had done it sooner and will absolutely replicate what I have when it is time to replace it.

    1. Expert Member
      Dana Dorsett | | #18

      You realize Rich posted that more than nine years ago, right?

  15. Expert Member
    NICK KEENAN | | #15

    I run a dehumidifier and a HP water heater. The dehu kicks in when the HPWH doesn't remove enough humidity. All of the latent heat from the humidity that is removed by the dehu is put into the room and available for the HPWH. The basement is the most comfortable room in the house, 68F and 45% RH. I find this an excellent combination for basements where the latent load is higher than the sensible load.

    1. jvidamins | | #21

      This is exactly what I was thinking of doing. Definitely going with a HPWH and thinking of adding a dehumidifier into the same basement utility room as the it creates heat and the HPWH works eats heat. Sounds like the perfect combo and the utility room will no longer be the coldest room in the house (like it would be without the dehum).

  16. Jon_R | | #16

    Data I've seen shows that the amount of dehumidification provided by a heat pump water heater is minimal (like < 1 liter/day).

    1. hotwaterbob | | #17

      I haven’t measured the condensate as it goes directly into a sump hole, but I can tell you is the RH is about 45% when my HP is running in the summer.

  17. Expert Member
    Dana Dorsett | | #19

    The amount of dehumidification depends a lot on the amount of hot water used. The heat pump has to be running to provide any dehumidification benefit.

    The heat pump doesn't run (much) when no hot water is being used, but would run quite a bit in homes where a full flow shower runs an hour or more every day.

    1. Expert Member
      NICK KEENAN | | #20

      It also depends on how humid the basement is and what temperature it is. Anecdotally I once had a HPWH where I couldn't install a drain right away so I had it drain into a 5 gallon bucket. That bucket needed to be emptied every few days.

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