Home’s humidity relative to area and temperature

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This article was published 05/10/2003 (8234 days ago), so information in it may no longer be current.

QUESTION — I have to ask about the humidifiers my husband and I recently had installed in our house. It’s a 10-year-old, 3,300-square-foot bungalow and the rooms have ceilings that are nine to thirteen feet high. We haven’t had problems with dryness until this winter as we’ve been absorbing the humidity from a new building, as well as the moist outside air intake for the furnaces.

We have two furnaces, one on each side of the house, both of which have fans that can be turned on to circulate the air. We also have two gas fireplaces that we burn every day in the cold weather last winter, which I assume causes the furnaces to kick in less often. We keep both thermostats set at 67 F and a humidistat device we bought reads a level of around 25 per cent in both areas.

When the humidifier installer came to do the work, he commented that the air was very dry, asking for a drink of water because he felt parched. I am suffering from a very itchy scalp and my husband and my daughter’s skin is flaky. But when we try to turn up the humidifiers, we inevitably find ice at the bottom of the windows, which melts when the sun warms, and I am worried that it will eventually damage the frames. When I called the company about this, a person told me that ice is forming because the air is saturated and can’t hold more water, but the reading is still 27 per cent. I have tried turning on the fans all day to circulate the air but it doesn’t seem to make a difference. I would appreciate your opinion as to what we should do next. We’re beginning to believe that we wasted the money on these devices that don’t work at all. I should add that the windows are Willmar heat-mirror and we have many, on the south side of the house predominantly. The installer has replaced a gauge in one of the humidifiers because it clicks barely above zero.

–Diana Baran, e-mail

ANSWER — The topic of humidity and moisture in homes is an extremely complex one and may be quite technical, but I will try to answer your question in a straightforward manner. I may not be able to offer a simple solution to your problem, but will try to explain what you are experiencing. The readings on your measurement device do not tell the whole story. The humidity in the home is "relative" as it may vary considerably due to different temperatures in specific locations. The relative humidity may be much higher in the basement or near a cool exterior wall than it is near the warm fireplaces.

Relative humidity is the percentage of the total amount of moisture that air can hold at a given temperature. The warmer the air, the more water it can hold. Once the relative humidity exceeds 100 per cent, and the air becomes saturated, condensation will occur. This can be achieved, simply by a drop in temperature. That is why you are seeing a relatively low reading from your measurement device and yet have condensation on your windows.

The device is measuring the relative humidity of the air in a warm location in the home, far away from the much cooler windows. When the warm air hits the cool window, it drops below the "dew point" and condensation occurs on the glass. It is often difficult maintaining a proper level of relative humidity within a home in the winter that is comfortable for the occupants and still healthy for the house. A comfortable level for humans may create excess moisture in the home, including the condensation seen on your windows.

In most new homes, adding moisture to the air in the heating season is not necessary due to the high level of air sealing employed by current builders. This is accomplished with good air-vapour barriers, weatherstripping, and high quality doors and windows. The windows in your home are an example of a high quality window with added components for increased energy efficiency. The problem with most new homes is normally eliminating excess moisture due to this tightly sealed environment.

The fresh air intakes you mentioned serve to bring in relatively dry outside air which helps replenish moist house air exhausted through fans, normal ventilation, and the fireplace chimneys. These will reduce the moisture in your home in winter, not increase it. Fireplace use may create areas where the relative humidity in the air appears low, due to the warm air blown from the units, but may actually be at a reasonable moisture level. Minimal or moderate use of the fireplaces will prevent localized areas of high temperature air, and may help the situation.

The humidifiers add moisture to the house through the air circulated by the furnaces. If the fans are on continuously, this may increase the amount of moisture in the air, rather than reducing it. Humidifiers are often used in older, drafty and poorly sealed homes and may not be needed in your home, at all. You may want to try altering your current heating methods for a few days, to see if improvements are seen.

Shut off the humidifiers completely, avoid using the fireplaces, set the thermostats to normal levels and leave the furnace fan on continuous low and observe the results. You may find that the window condensation is reduced, and the house has a more comfortable moisture level. If this does not help, consult an HVAC contractor or consultant that specializes in air quality control. They can do tests and measurements to determine the best use of the systems in your home or offer a better alternative.

Ari Marantz is owner/inspector of Trained Eye Home Inspection Ltd. and is the P. R. Rep. for the Canadian Association of Home & Property Inspectors- Manitoba (www.cahi.mb.ca). Questions can be e-mailed or sent to: Ask The Inspector, P. O. Box 69021, #110-2025 Corydon Ave., Winnipeg, MB. R3P 2G9. Ari can be reached at (204) 291-5358.

trainedeye@iname.com