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NORA Advanced Efficiency

National Oilheat Research Alliance 35 drawn into the building to replace the warm air that was lost through all the leaks. State-of-the- art sealed homes can have as low as one half an air change per hour. Additionally, air leaks create drafts that occupants may notice. After the heating system, finding and sealing air leaks should be the top priority. Home Performance Contractors use a device called a Blower Door to measure and find air leaks, Figure 8. It is a large, variable-speed fan they place in an open outside door. It draws enough air out of the building to make the pressure difference between indoors and outdoors 50 Pascals. By determining the cubic feet of area inside the air and thermal barriers, and the speed the blower has to run to achieve negative 50 Pascals, they can compute how big the leaks in the building are. When the building pressure is far below the outdoor pressure, the air leaks become obvious and are easy to locate. If there is a temperature difference between inside and outside, a thermal imaging camera will quickly identify gaps in the Thermal Barrier (Insulation). Heat Flow is Dominated by the Weakest Link It doesn’t matter how thick the fiberglass is piled if there are gaps and missed spots. Gaps in insulation of just 5% in an R-40 attic will triple the heat loss! The typical leaky attic hatch accounts for about 5% of the surface area of the attic floor. A bypass is a place where air escapes the building thru chimneylike leaks. The effects of a by-pass are heat loss, moisture transport, and higher negative pressure in the building (sucking in more cold air). Typical by-passes: chimney and plumbing chase, tops of partitions and exterior walls, floor-knee wall transitions, and balloon frame construction. Insulation The most common way to describe insulation performance is R-value. R-value describes a material’s resistance to conductive heat transfer. Materials with low resistance to heat transfer have low R-values: glass, steel, concrete, wood, and wallboard. Materials with higher resistance to heat transfer have higher R-values. R-values for a wall or ceiling can be added but not averaged. They are like a sandwich. Each layer has a different R-value. To determine the total R-value of a square foot of wall, add together the R-values of all its layers. USDOE minimum recommended R-values for existing homes in New England: Ceilings and attics:R-49; Sloped roof: R-38; Walls: R-19. Insulation slows heat transmission Air is a poor conductor. It is a heat sponge. It absorbs heat and carries it with it if it moves. Insulation’s job is to trap the air and not let it carry heat away. Insulation also reduces radia- Figure 8 Blower Door


NORA Advanced Efficiency
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