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Community and Q&A

Sealing Old Dryer Vent Hole in Wall

rondeaunotrondo | Posted in General Questions on

I purchased a heat pump dryer on my way to going combustion free. Got rid of a 30 year whirlpool gas dryer (still working!). What is the best way to patch the hole out of the exterior wall? It runs above the sill, old wooden shingles with vinyl on top. Zone 5, 1915 Bungalow.

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  1. PBP1 | | #1

    A heat pump dryer will to some extent increase humidity in the room (not all of the moisture goes down the drain), if it ever gets bad, you may want to consider a "reversible" solution such that you can install a humidity sensor triggered exhaust fan that uses the "old" dryer exhaust vent. Not saying it will ever be needed, but it may be in the realm of possibilities. I have two dryer exhaust vents installed per code and a heat pump dryer (nothing hooked up to other). I have stuffed the vents with wadded up packing foam (foam sheets wadded up, about the thickness of dryer sheets - noting that I do not use dryer sheets).

    1. jwasilko | | #8

      We have a Miele heat pump drier installed in a small bathroom, and it doesn't seem to increase room humidity at all.

      1. rondeaunotrondo | | #15

        We just bought the Miele W1/T1 base models. Expensive But a good amount of rebates and longevity. Going from a 30 yo dryer and 10 yo top loader made for a big difference.

  2. rondeaunotrondo | | #2

    Thanks PB for your comment, however, I also will be installing a HP water heater in the same space so they will offset each other. I also don’t want a hole in the wall. Hence, I would like a permanent solution.

    1. steve_smith | | #3

      I recently replaced my gas dryer and water heater with heat pumps. They are only a couple of feet apart in my garage. Even with this setup, the humidity increase is very noticeable. I live in a relatively mild climate and have left the vent hole open for the time being, but the idea of a humidistat controlled fan is not one that I had considered.

  3. irene3 | | #4

    I don't quite see how the dryer and the water heater (which both pull heat from the room air) would offset each other, especially as regards moisture in the air. Moisture gets added to the room air from the clothes being dried in the dryer, but the water heater doesn't absorb any of that moisture.

    The dryer offsets itself to some degree, as heat from the dried clothes dissipates and warms the air again rather than being sent outside through a vent, but it doesn't offset the cooling caused by the water heater.

    1. Expert Member
      NICK KEENAN | | #5

      The heat pump dryer introduces quite a bit of heat and some moisture to the air. The heat pump water heater removes humidity from the air and heat. Whether they balance each other out depends on how much each is used.

      1. jwasilko | | #9

        Our Miele does neither. The bathroom isn't warmer or more humid.

        1. Expert Member
          NICK KEENAN | | #10

          The energy consumed by the dryer has to go somewhere.

          1. jwasilko | | #11

            Both the hot side and cold side of the heat pump are in the air flow. The air is heated, run over the clothes, filtered and then cooled to condense the moisture out, and then heated (and the process repeats).

            The dryer is sealed, so the process air doesn't mix with the room air.

            Since you're both heating and cooling the air, there's not much opportunity for net gain.

          2. Expert Member
            BILL WICHERS | | #14

            The heat added to the room will be the amount of wattage consumed by the dryer, minus some amount that went into condensing the water out of the air. More heat will be produced than was "cooled off" by the heat pump in the dryer. What you essentially end up with is this:
            Wattage coming in->
            ->Useful work of condensing water
            ->Losses heating up the room

            That's where the energy goes. It always has to go somewhere.


          3. Expert Member
            NICK KEENAN | | #16

            Since the water enters the dryer as liquid and leaves as liquid there's no net heat flow from phase change.

            I will concede that some heat leaves the dryer in the waste water.

          4. Expert Member
            BILL WICHERS | | #18

            Interesting point DC, I hadn't considered that. The water DOES start out liquid (in the clothes), then evaporates and gets re-condensed again. I suppose that would constitute a closed system.

            I do agree regardless that the majority of the input electrical energy will leave the unit in the form of heat, which will ultimately warm up the room the dryer is in.


        2. Expert Member
          NICK KEENAN | | #13

          Every electric device releases heat exactly equal to the energy content of the electricity it uses. My understanding is that the Miele dryers use about 750 watts. It may not be noticeable but the heat is there.

  4. GBA Editor
    Kiley Jacques | | #6

    Hi Will,

    The same question was asked a while back, and this is how Martin Holladay answered it:

    Only you can decide whether you want to permanently remove the vent termination, or whether to keep it for possible future use. I would probably keep it -- a future homeowner may appreciate it.

    From the interior, you can pack the inside of the duct with fiberglass or mineral wool insulation, and then you can install an airtight interior seal (either a gasketed piece of attractive wood -- basically, a small panel -- with 4 screws, or taped drywall).

    1. rondeaunotrondo | | #7

      Thanks Kiley, I searched and couldn’t find an answer. We plan on being here a long time so I would like to permanently remove it. I can’t find any description of the detailing of this. We will be insulating the rim joist soon so I will likely do it then but not sure if the detailing outside given siding etc. I may turn it into an external electrical outlet since there are none outside.

      1. Expert Member
        BILL WICHERS | | #12

        I would propose cutting a circle of rigid foam to plug the hole, sealing the circle in place with canned foam. Use some trim board (I'd use a small piece of PVC trim) to cover the hole on the exterior and flash/caulk that into your siding to provide weatherproofing. If you ever want the hole again, it would be easy to remove this "plug", but you'd have a permanant assembly that would be fairly good in terms of insulation/air leakage too.


        1. rondeaunotrondo | | #17

          Thanks Bill. What do you think about turning this into an electrical outlet? Again, I have no need to keep it. It’s an open basement and I have moved the dryer near the washer (and drain) so it will never be used again as a vent.

          1. Expert Member
            BILL WICHERS | | #19

            I see no problem doing that. Insulate the hole as I described, then just poke a wire through and seal it with canned foam. Easy to mount a box to the exterior trim piece.


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