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Fri, Feb. 28

Column: Test home for energy leakage

Blower door and duct test in progress.
Courtesy photo

Blower door and duct test in progress.

Question: Help, my energy bills are very high, and my home is always cold and draughty in winter and hot and sticky in summer. What can I do?

A: All buildings continuously lose energy in the form of winter heat loss and summer heat gain, and that heat and cooling loss needs to be continuously replaced by your heating and cooling system. This primary energy loss comes from poor insulation, and outside air infiltration through holes in the homes envelope (outer walls and roof). In reality up to 40 percent of a home’s energy can be lost through air and moisture leakage.

Air leaks are driven by air movement based on air pressure and temperature differences. The earth’s atmosphere is continuously changing with low and high pressure systems building and declining. As they do, air movement equalizes pressure in the form of wind. As wind hits a building it creates a high pressure point on one side, and the opposite side becomes a low pressure point; holes in the building envelope leak air into and out of the structure, causing drafts and temperature differences.

As temperatures rise in a building the air expands, volume increases and pressure drops; as temperatures drop the reverse is true. Therefore, warm air always rises and cool air sinks. In winter warm air rises and leaks out of a building at high elevations, as it does cold air replaces the warm air through lower level leaks causing drafts. In summer the process reverses. As an example, a typical home not designed for low leakage leaks around 143 cubic feet of air a minute. This leakage represents an open window measuring approximately 14 inches by 14 inches 24 hours a day 365 days a year.

Leaks not only waste energy through air infiltration, they also allow moisture, insects, dust and pollutants to penetrate internal cavities. Moisture vapor molecules are lighter and smaller than air and can go where air cannot. In cold climates the outside air can condense in walls and the attic causing moisture damage. This moisture damage reduces the effect of insulation; it also encourages mold, mildew and fungi buildup that can create health problems for occupants.

Other effects of leakage include internal humidity changes; in cold climates excessive leakage will dry out internal air. This happens as internal warm moist air is replaced with outside cold dry air. A common effect of dry air is static electricity and personal electric shocks when touching grounded electrical appliances. When the cold incoming air is wet it creates condensation buildup on walls and in the attic causing rot and bacterial damage. In summer the opposite exists, the cool dry air is replaced by incoming warm moist air and the hot sticky humidity effect increases; putting more stress on an air conditioning system to remove the heat and the humidity.

When considering energy conservation and living comfort, the air that is being forced in and out of a home through leaks due to wind and convection should be prevented. Sealing a home effectively with an air and moisture barrier will significantly reduce both winter and summer energy loses, improve occupant comfort, significantly reduce pollutants and keep out pests and noise. A blower door and duct test will tell you how good or bad your leakage level is.

You can get these tests by contacting APS and asking for the $99 energy test package, but remember to ask the technician for the leakage test results as they don’t generally give them out without asking. The technician should be able to give you an approximate air change rate for your home. If not, you will have to make the calculation. The blower door test amplifies the leakage level to a 50 pascal pressure level, or 20 mph wind equivalent. Its result will be in cubic feet per minute (CFM50). To change this into air changes per hour, multiply the CFM by 60 minutes and divide by the house volume in cubic feet, this will give you ACH50. The 2012 IECC specifications require that new buildings in Prescott have no more than 3ACH50; however older homes will exceed that; ideally an energy efficient home will be between one and two ACH50, and a very leaky home will exceed 5ACH50.

For more information, contact Paul Scrivens, Green Home Energy Advisors, .

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