Do Dehumidifiers Really Help Moisture Levels?


We’ve talked about the need to maintain moisture levels in your home many times (here, here, and here) but does a dehumidifier really help? In 2009, a research study from the Canada Mortgage and Housing Corporation studied just that. The exact purpose of the study was to examine how effective dehumidifiers are at controlling the moisture in homes in different regions of Canada.

The Setup

The study took place over a period of two years with 30 homes participating from 3 regions of Canada. All of the homes chosen did not have dehumidifiers installed prior to the experiment. Furthermore, they did not have HVAC systems installed, and had not experienced flooding in recent years.

In order to track temperature and relative humidity (RH), each home had one data logger placed in the basement and one date logger placed on the main floor. The data loggers were programmed to take measurements on an hourly basis. To measure wood moisture content, moisture meters were placed at 7 locations throughout all levels of the home. In addition, infrared thermometers provided surface temperature measurements in 12 locations.

Measurements were noted on a provided log sheet by the participants on a monthly basis. The dehumidifiers used for the experiment had a capacity of approximately 65 pints per day and included a 2.64 gallon water reservoir. While being used for the experiments, the dehumidifiers were set to maintain 50% relative humidity. The units had a built in RH sensor that automatically maintained this humidity level. Once the dehumidifiers were in place participants also started tracking the volume of water that was extracted by the unit.

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The Experiment

The first year of the experiment was used to establish a baseline for measurements. None of the homes had a dehumidifier installed and the data recorded during this time was simply meant to outline normal characteristics of each home.

After year one was finished, 22 of the homes agreed to move forward with the dehumidifier phase. It was during the second year that a dehumidifier was installed in each home to determine if it could reduce moisture issues.

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The Results

Once the two year period was completed, results were gathered from 21 homes. Since results were based on participants taking data, some homes had significant lapses in data making their results unusable. After the data was examined, it was determined that 18 homes had acceptable data to be analyzed.

All of the homes that were analyzed demonstrated moisture removal once the dehumidifiers were installed. More than half of the homes showed an overall reduction in indoor humidity levels, with seven homes showing a reduction in wood moisture content. House 22 provided detailed data findings and thus, was used as an example for the results. During year 1, with no dehumidifier installed, the absolute humidity in the basement varied greatly. For instance, in February, the outdoor absolute humidity was approximately 3 g/m3 while the basement absolute humidity was approximately 5 g/m3. Conversely, in July, the absolutely humidity outside peaked at approximately 13 g/m3, while the basement absolute humidity rose to 17 g/m3.

Once a dehumidifier was installed in House 22, the indoor absolute humidity was much more consistent. In February of year 2, the basement absolute humidity was slightly lower but still around 5 g/m3. Instead of rising dramatically during the summer, however, the humidity level in July was only 8 g/m3. This data matches the dehumidifier moisture removal rate. During the winter months, no water was collected from the dehumidifier. During the summer months, when humidity levels outdoors are higher, the moisture removal rate by the dehumidifier was also at its highest.

The wood moisture content in House 22 also improved once the dehumidifier was installed. During year 1, the wood moisture content peaked at 10% between June and October. With a dehumidifier maintaining the space, the wood moisture content remained a steady 7-8% throughout the year.

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Conclusion

The study concluded that dehumidifiers were an effective way to reduce humidity levels. During the warm, humid months, while the dehumidifier was in use, the absolute humidity levels were lowered compared to year one. Furthermore, the dehumidifier helped maintain a consistent humidity level throughout the year. By reducing the indoor humidity levels, the dehumidifier also lowered wood moisture content levels and helped prevent moisture issues such as mold and pests.

While the study only examined the use of dehumidifiers in a basement, it can be concluded that a crawl space dehumidifier would yield identical results. Installing a dehumidifier in your crawl space would reduce the humidity levels in your home, as well as all of the benefits such as reduced risk of mold and pests.

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Canada . Canadian Mortgage and Housing Corporation. Effectiveness of dehumidifiers in controlling moisture in houses. Vol. 9. Ottawa: CMHC, 2009. Print. Ser. 106.