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Community and Q&A

Ducting Hybrid Water Heater / Heat Pump Intake Air

drewintoledo | Posted in Energy Efficiency and Durability on

Now this may not be code, but in theory would it make any sense to duct a hybrid water heater/heatpump intake air into the attic and pull the hot air out to dump into the water?    Or, how about pulling hot air from the attic to dry clothes in a clothes dryer?  It sure seems like there is a missed opportunity here.

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  1. Expert Member
    DCcontrarian | | #1

    The attic isn't always hot. How would you make sure you're only pulling air when it's hot?

    1. drewintoledo | | #4

      Schedule the heater for heating during the day. I currently have the temp turned down during the night while we sleep.

      1. Danan_S | | #9

        > I currently have the temp turned down during the night while we sleep.

        I don't know about Toledo, but around here the lowest electricity rates tend to be at night when we sleep (after midnight), so that's usually a good time to run the water heater. I'm not sure that turning the temp down nightly on a water heater has much effect on energy $ savings.

        If you have flat electricity rates (which are going extinct in many places), it makes even less sense to time shift your usage.

        1. drewintoledo | | #10

          Flat rate here, so it's more of not heating while not needing it type of thing..

          1. Danan_S | | #12

            Modern water heaters are so well insulated that I doubt that would save much energy.


        2. greenright | | #11

          In the northeast TOS rates are actually getting extinct. Eversource used to offer them- not any more. One flat rate all the time seems to be the norm. Go figure.

          And yes- I had the same idea- attic temps are high even during the winter if the sun is out. Easiest solution would be air intake for the hot water heater with a diverter/ damper controlled by simple logic- if temp in attic is over xx degrees open damper to attic. Otherwise open damper to indoor. This is very simple automation.

  2. Expert Member
    BILL WICHERS | | #2

    I don't think that will really help you all that much. It's true that you'd then be scavenging heat from slightly warmer air that was heated a bit from energy lost through your attic floor insulation, but I think you'd be better off just putting more insulation on that attic floor to cut down on the losses in the first place.

    I would NOT bring attic air down to run a clothes dryer. Attic air isn't usually air that you want to bring into your living space.


    1. drewintoledo | | #5

      I figured it would be air being heated from the roof inwards into the attic instead of heat rising. Most attics I have been in have been pretty hot, especially in summer and it was way too hot to have been heat coming through attic floor. Had to be the sun!

      1. Expert Member
        BILL WICHERS | | #7

        In the summer, that extra heat would REDUCE the efficiency of your heat pump during the cooling season. It would tend to have a high moisture content which wouldn't be helpful for your dryer. In the winter, ideally that attic air won't be much warmed than outdoor ambient, so you don't really gain much.

        As an aside, I have often wanted to use the waste heat from datacenter facilities to heat the adjacent office space. It seems pretty wasteful to pay for energy to cool one side of the wall, and pay for energy to heat the other side of the same wall! The problem is the economics of the system almost never work out, which is unfortunate. About the best I've been able to do at a somewhat large scale is to use some of the waste heat from the chillers to run a snow melt loop under the parking lot. This avoids the need for salt and plowing, so at least that waste heat is doing something useful.


        1. drewintoledo | | #8

          You talked me out of it! :)
          I'm with you on the datacenter thoughts. I've been in IT for > 30yrs so I've been around quite a few datacenters. The datacenter where I currently work is a "hot" datacenter, so cooling is minimal. I need to wear a short sleeve shirt while working otherwise I will sweat pretty bad. Heck, even standing there typing on a laptop will make you sweat in this datacenter. I know Google runs a hot datacenter too, quote "We raise the temperature to 80°F". ( That's about the temp of our DC. I imagine the electronics don't care much and the host saves plenty of money. I'm sure you're familiar with liquid cooled rack doors where the heat can be harvested? ( Also, the underwater Microsoft datacenters? (
          I digress.

        2. greenright | | #13

          Three pipe VRF solutions do just that.. move hot air from data centers to office spaces in the winter.

  3. rockies63 | | #3

    So you want dirty, filthy air from the attic blowing all over your clothes?

    As to transferring the hot attic temperature to water, an air to water heat exchanger could work.......maybe.

    1. drewintoledo | | #6

      Great question! Nope. I have a heat pump dryer as well.

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