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Community and Q&A

Humidity control other than plug in De/humidifier

Terry Sharpe | Posted in GBA Pro Help on

Hi All,
I was wondering if there are any methods for controlling extreme humidity in the summer and extremely dry conditions in the winter that could be automatically implemented (other than just plugging in a humidifier or a dehumidifier).

I have a ground source heat pump in my 180 yr old stone house (uninsulated, because stone), and the humidity levels are extremely high in central Ontario in the summer (like, slippery floor level humidity) and extremely dry in the winter (furniture crackingly dry).

Is my problem as simple as ‘just go talk to a HVAC guy and get him to install a full humidification system’, and if so what sorts of things do i need to be aware of? Are there things i should be steering clear of or will a standard system just plug and play? What is this going to set me back and are there alternate ways of doing it? I’ve tried plug in dehumidifiers and humidifiers and they do pretty much nothing.


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  1. Alan B | | #1

    Its likely your house it not anywhere near airtight, which would allow high summer humidity, and high air exchange in winter lowering your humidity rapidly and keeping it low.

  2. Nate G | | #2

    …Of course, once you make your house airtight, you then need to poke some holes in it for ventilation. An ERV will address the moisture concerns ordinarily associated with ventilation and air leakage.

  3. GBA Editor
    Martin Holladay | | #3

    Alan is correct: Your house has the symptoms you describe because it leaks a lot of air. The solution is to do the best job you can of air sealing your home's envelope (floors, walls, and ceiling).

    The best way to do this work is to hire a weatherization crew or a home performance contractor familiar with blower-door-directed air sealing.

    For information on some of the required steps, see these two articles:

    Air Sealing an Attic

    Air-Sealing a Basement

    Until you reduce your home's air leakage rate, it's going to be impossible to try to control your home's indoor humidity levels.

    There will be an important side benefit to performing this air sealing work: in addition to helping you control your indoor humidity levels, you will lower your energy bills.

    Unlike Nate, I wouldn't worry too much right now about the need for a mechanical ventilation system. It sounds to me that your house is so leaky that you have a long, long ways to go down the air sealing road before you have to consider Nate's concern.

  4. Terry Sharpe | | #4

    Thanks for the responses guys. I agree that my house leaks like a sieve, but I think that was part of the design intent at the time and it’s hard to change now, and possibly not entirely beneficial. Allow me to explain before you have apoplexy. :)

    Wall construction is plaster over 18” of stone in one half, and the ‘addition’ (circa 1900 or earlier) is plaster over stackboard (which if you are unfamiliar with bizarre lumber town techniques of the turn of the century, is essentially true 2x4’s laid horizontally with about ½” chinking in between them, sort of like a log cabin. No need for lathe for your plaster though! it just goes straight onto the wall).

    Basically there is no place for vapour barriered insulation other than inside the walls, which is not an appealing option in the stone half due to lost living space, and while possible in the stackboard half, leaves a strong possibility of mold in the walls. I’m left with slowing down the air, rather than stopping it with vapour barrier, as plaster breathes readily and is designed to do so.

    Looking at the articles I don’t know if those apply to my situation either. The house is a story and a half, which means the second floor looks like it has a knee wall, except the vertical and the slanted ceilings are both exterior facing, with only the horizontal ceiling with something on the other side of it (the attic crawlspace). That has loose fill cellulose insulation on it, but most of the info there just doesn’t and couldn’t apply. The basement is stone, and I’ve re-pointed the mortar to seal it up, inside and out, and used expanding foam to stop any other air gaps. But my ‘rim joists’ are 12”x12” beams, and insulation on stone walls is at best a recipe for mold and is generally not done.

    I’ve done blower door tests and stopped any merry little breezes (it 'passes' the test at least), but essentially I’m left with the fact that the entire house is a giant lung. There’s no punctures in it but it still breathes regardless, and if you stop that function entirely it dies. Conventional wisdom just doesn't really work as far as I can tell.

    Am I just screwed for humidity control or are there options that can at least slow it down? I don’t expect hard stop solutions but will be happy with soft ones, things that can help if not solve. Will a humidity solution at least help? Like it’s not like the house can’t be heated or cooled at all so I’m not just pouring it into the great outdoors – is humidity something I can find a half measure for as well?


  5. GBA Editor
    Martin Holladay | | #5

    It's hard to control either the temperature or the humidity levels in a house like the one your describe. While you are sure that it's impossible to perform air sealing work in a house like yours, I can assure you that weatherization crews have seen homes like yours before.

    You are correct that some homes are more difficult to air seal than others. But air sealing work won't cause your house to rot. I suggest that you try to tighten up your house.

    If you don't want to take that path, the choice is yours. But it's very hard to try to dehumidify or humidify the great outdoors.

  6. Terry Sharpe | | #6

    Fair enough. I'll look into the weatherization and see what's possible.

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