The introduction of blower doors
to weatherization providers has greatly increased their effectiveness by allowing them to accurately locate the holes in the building envelope where outside air infiltrates indoors. (Credit: David Saum, Infiltec) |
Blower doors are variable-speed fans equipped with a frame and shroud that permit them to fit inside a variety of doorframes. The instrumentation includes pressure gauges that enable the operator to determine the flow of air through the fan as well as the pressure the fan induces on a dwelling. Since leakier houses require more airflow to induce a given pressure difference, blower doors can measure the relative leakiness of a house.
Blower doors can also reveal the location of many leaks, thus providing a clear target for air sealing. When the job is partially or fully complete, blower doors also provide technicians with quick feedback on the effectiveness of their work. In addition, blower doors can help diagnose which parts of a house do not need to be sealed. This allows weatherization crews to focus on the real problems.
Blower door technology has contributed significantly to the evolution of weatherization and building science. Before the advent of this technology and the detailed analysis of patterns of convective energy losses that it allows, most air leakage was thought to occur toward the mid-height of the conditioned building envelope, primarily through doors and windows. Accordingly, DOE and weatherization professionals advocated weatherstripping and caulking in those areas. In fact, blower doors do reveal leaks from doors and windows, although their effects are amplified, since small areas result in high-velocity air currents.
However, leakage from doors and windows represents a relatively small percentage of convective losses in most dwellings, and serious leaks tend to occur at the bottom and especially at the top of the conditioned envelope. As a result of the widespread use of blower doors, weatherization crews increasingly seal the air in attics and basements where most air infiltration into the house takes place.
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