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Community and Q&A

Indoor air quality

user-234358 | Posted in GBA Pro Help on

Hello GBA!

We are looking for solutions to help with the indoor air quality of our home. We live in the Minneapolis, MN area and have switched our home from forced air to a hydronic system. This was done to enable us to remodel our home to better suit our needs. Due to this change and the tighter envelope of our house, we are experiencing the typical condensation on our windows during the winter. Are there any ideas out there that may help us control the air quality inside our home?

Thanks for the help!

Mark and Melani

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  1. SLSTech | | #1

    Control the moisture you create - cooking, washing dishes, showering - turn on the vent & leave on as needed
    If you have a ventless heater, fireplace, etc... - get it out of there
    Look for other sources of moisture & find a way to control them or stop them from entering - ground sloped away from house, sump pump, etc...
    Interior or exterior storm windows
    get a dehumidifier

  2. dickrussell | | #2

    One of the first things learned from the first superinsulated house built by pioneer Gene Leger was the need for mechanical ventilation in a super-tight house. He said as soon as they moved into the house, they found that it was like "living in a baggie," in January! Right away he realized his mistake in not providing for way to get rid of the moisture produced by human occupancy (and from building materials drying out in the first year). He bought a small air-to-air heat exchanger (today we'd call it an HRV), cut a hole in the wall, and installed the unit, much as you would an in-wall air conditioner.

    Builders often have claimed that you can't make the house too tight - "the house has to breathe." This is nonsense. The people have to breathe, and the house has to avoid moisture related issues. There is no way to build in the "correct" amount of leakiness. Any house in a heating climate will leak air the most when it's bitter cold and windy outside, which may still be inadequate in a tight house or still too leaky for energy conservation. In mild, windless weather the house won't leak air at all.

    A good job of energy conservation requires a very tight house, toward which your remodel has moved, but nothing should be done to the shell of a house without considering the impact on the rest of the shell and indoor conditions. For now, yes, you can leave the bathroom vent fan on around the clock, or at least much of the day. However, that will force fresh air to come in via the myriad cracks and holes in your building shell. Do you really want to use the walls as an air filter? Unless you have unusual moisture sources in the house, as Sean suggested, your best bet for the long haul might be to install a heat recovery ventilator and distribute the incoming air to various places here and there in the house.

  3. GBA Editor
    Martin Holladay | | #3

    Fortunately, it's fairly simple to solve the problem you describe. Just increase the home's ventilation rate. If your home has a bathroom exhaust fan, leave the fan on for 24 hours a day until you no longer see any condensation on your windows.

    I disagree with Sean. You don't need a dehumidifier during the winter. The outdoor air is (almost) always dryer than the indoor air during the winter, so all you have to do is ventilate. This will use much less energy than operating a dehumidifier.

    Once you have reduced the immediate problem, you can make a long-term plan about the best mechanical ventilation system for your home. Among your choices are an exhaust-only system or a system with an HRV. For more information on these options, see Designing a Good Ventilation System.

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