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Is there a ventless / heat pump option for bathroom exhaust?

Phil Dennis | Posted in Mechanicals on

Hello.

I am designing / building my first passive house. I am located in Nova Scotia, currently working out the details for my HRV/ERV system, and evidently confronted with the issue of bathroom exhaust fans.

I have been offered the same advice as most; from controlling the humidity peaks with the HRV/ERV system to traditional venting directly outside.

I am not keen on the idea of relying on my HRV/ERV to handle bathroom humidity (not to say it cannot work if designed correctly), and I am not interested in compromising my air barrier with the traditional approach.

Does anyone have any experience with a whole-house bathroom humidity control system with a heat pump? A closed-system, entirely inside the building envelope, and independent from the HRV/ERV? Perhaps similar to the concept of a heat pump dryer.

I am unsure as to how this would affect the HRV/ERV system-balance when active, and also if there would be any issues with the local building code.

I am open to any ideas or feedback.

Thank you.

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Replies

  1. Charlie Sullivan | | #1

    A heat pump based closed-system humidity control system inside the building envelope, similar to the concept of a heat pump dryer, is commercially available. It is called a dehumidifier. I have heard of people using stand-alone dehumidifiers as a makeshift approach to controlling humidity in bathrooms that are lacking vents. There are central ducted dehumidifiers available, and you could certainly use one for that purpose. Dehumidifiers add heat to the space that they deliver the dried air to, so that makes it a reasonable use of energy in winter. If the ducting is done well and independently, if would not affect the HRV balance. You could possibly share ducting with the HRV, but that would require a lot of careful design work and perhaps oversized ducts to make sure it works.

    But overall, that sounds like an expensive and complex way to deal with bathroom humidity.

    Venting bathrooms is not only for humidity control. It's not generally discussed in polite company, but unpleasant odors are sometimes generated in bathrooms. So having HRV/ERV exhaust from bathrooms is still a good idea.

    If you've got HRV exhaust from bathrooms already, that's likely to be sufficient for humidity control. If you are worried about it, you can get a modestly oversized HRV system with ECM fans. You can run them at low speed most of the time and set them to high speed when you want to clear out moisture from the bathroom quickly. The result would be very high electrical and heat recovery efficiency in normal operation, at a lower cost than adding a separate dehumidification loop.

  2. Donald Endsley | | #2

    Sure it's called a dehumidifier. You probably need to rig up a system to pull the air from the ceiling area where water vapor will accumulate first, and reintroduce the dried air at about floor level. That will create a thermal and mechanical push or draw through the dehumidifier. You will still need some form of powered vent to help deal with the stinky times, and likely easier code compliance, but you won't have to use it all that much.

    The size of the dehumidifier I can't really help you with. I'd bet Martin or Dana have a pretty decent Idea on how much water vapor a typical 120ºF Shower at 2.5 gpm puts out. Of course showering habits, water temperature, and actual shower head water flow will affect that.

    There may very well also be a health reason not to. The bathroom typically has a fairly high load of Fecal Coliform and E. coli bacteria, and this may help spread those in the bathroom, My gut (and knowledge of how they travel and grow) tells me this shouldn't be a problem, but I'm not comfortable saying that it really isn't going to be one until I see some test results.

  3. Stephen Sheehy | | #3

    My HRV on boost does a fine job exhausting bathroom humidity and odors.

  4. Phil Dennis | | #4

    All good answers. Thank you for your feedback.

  5. Expert Member
    Malcolm Taylor | | #5

    Phil,
    It's worth seeing hat your code says before going much further.I don't know if Nova Scotia enacted the same energy amendments as BC, but we are required to have mechanical ventilation in all bathrooms and can not rely on alternatives such as operable windows or dehumidifiers.

  6. Phil Dennis | | #6

    Good point Malcolm.

  7. Jon R | | #7

    My concern would be that a typical dehumidifier can't keep up with shower moisture in real-time. So condensation running down the bathroom walls. Maybe OK with help from a HRV.

    You could ventilate the bathroom to the house interior - might be code compliant if the bathroom has a window or a HRV intake.

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