New Tools, Better Results
These air leaks seldom get addressed during traditional home improvements because they're not visible from inside the conditioned space; they're concealed inside framed cavities, behind drywall or plaster. But with modern diagnostic tools, it's possible to find them and to complete an accurate, detailed heat-loss assessment of a home in just a few hours.
Using an infrared thermal camera in conjunction with a blower door, an energy auditor can identify leaks in the air envelope and insufficient or missing insulation in the thermal envelope.
On a typical job, I first set up the blower door and depressurize the house to 50 pascals, relative to the outside. This approximates the range of pressures a building would be subject to on a very windy night and helps establish a consistent benchmark for comparing the leakiness of one building with that of another.
The blower-door fan draws outside air in through penetrations in the shell and exhausts it through an entry door. The calibrated fan measures the cubic feet per minute of airflow required to maintain the 50-pascal pressure difference between inside and out. The draftier the shell, the higher the flow in cubic feet per minute. Simple math helps us convert the cfm reading to a whole-house air-exchange rate, stated in air changes per hour.
With the blower-door fan running, I make a visual inspection of the home, looking for any obvious leakage spots. A smoke pencil — a handheld device that emits a stream of chemical smoke — helps in tracing drafts.
With the blower door running, the author uses a smoke pencil to detect leaks in the house's air boundary. The leaks shown here — at a window sill.
A plumbing penetration in a base cabinet.
One of several can lights — were the result of a kitchen remodel that left the home feeling draftier than before.
After the blower has been running for a while, drawing in cold outside air, I take another tour through the house, this time using the infrared camera to scan for hidden air leaks and thermal bypass problems. The thermal image viewed through the camera reveals the radiant temperatures of the surface scanned. Since the R-values — and therefore the resulting temperatures — of an insulated bay and the adjacent wood framing members are different, it's simple to identify the framing details as well as weak spots in the insulation (Figure 3). Thermal scans often reveal areas where the insulation has settled or is not dense enough, and wall and ceiling bays that were completely missed when the insulation was installed.
The darker spots in these thermographic images indicate the presence of cold in framing cavities behind the drywall surface — areas where cold air has infiltrated or heat has been lost through conduction.
The framing around a Palladian window lacks insulation, while the ceiling area above suffers from wind-washing at the eaves.
An interior soffit is cold because the batt insulation does not make good contact with the drywall
The gap around the ceiling register is drafty. The uninsulated wall around an interior fireplace is chilled from cold attic air dropping down through the vertical chimney chase between the framing and the masonry.
Because the blower door is drawing in cold air from the exterior or attic, the scan can identify and measure areas of air infiltration, recognizable by a plumelike thermal pattern.
Wind-washing — air moving under and through the ceiling insulation at the eaves — degrades insulation performance, as is evident from the dark areas in the ceiling next to the exterior wall.
Around an exterior door show up in a typical plumelike pattern.
The scans also show areas where the wall surface has become chilly, indicating that the cold air is moving through or beneath the insulation. These spots are common on ceilings near the eaves, due to the effects of wind-washing (outside air moving into the eaves and through the fibrous insulation), but they can also show up in interior locations where you might not expect to find them.
The infrared scan revealed an unexpected cold area in this interior partition wall, which was traced to air leaking into the attic along the top plate, shown here being sealed.