Your household heating system’s equipment is only part of the equation. The efficiency of the building envelope (outer walls, floor, ceiling or roof) also requires attention. A heating system provides heat and the house uses (or wastes) it, in exact balance.

The heating equipment takes about 15¢ from every dollar of energy cost to operate itself. The house takes the remaining 85¢. While increasing heating equipment energy efficiency is worthwhile, the major saving is found in controlling heat loss from your house.

To increase the economy of heating, most homeowners automatically assume that insulation is the answer. However, insulation is not the whole story. Actually, in most homes air leakage is the biggest robber of heating dollars.

Houses leak air because of the difference between indoor and outdoor air pressure. Imagine your house as a hot air balloon. The biggest pressure differences are high and low in a building. Holes in these areas typically leak more air than holes in the middle. Warm air rises and leaks out any unsealed areas at the top of the building. Leaks inward tend to be at the bottom of the structure, pulling in cool air.

"Airtight" homes are more economical and more comfortable to occupy, if proper ventilation is provided. There are no drafts, only controlled air flow. They are more durable, too. In leaky houses, moist, heated air escapes into cooler areas, such as insulated walls and ceilings. There, the vapor condenses, which can cause mold, mildew, rot and other moisture-related problems. In Western North Carolina, this is the number one maintenance problem the homeowner faces. It is also a major source of allergy symptoms.

In the past, finding air leaks in a house was a hit or miss proposition. Now we have an objective three-step process to find and fix leaks in houses. They are: 1) Finding air leaks, 2) Fixing the problem areas, and 3) Verifying that the leaks have been sealed.

A blower door is used to both find and measure air leakage. The number of air changes per hour (the complete replacement of the indoor air volume of the house in an hour) at a standard pressure differential (pressure inside the house minus pressure outside the house, measured in Pascals) tells us how the house is performing, and where problems are.

The blower door test places a home under a known pressure and then measures how much airflow is required to maintain the pressure difference between indoors and outdoors. The tighter the house, the less air the blower door must move to maintain a given pressure. Besides measuring the airtightness of the house, it also helps to pinpoint specific air leaks.

Five air changes per hour at 50 Pascals differential pressure (5 ACH50) is a reasonable performance standard for our area. Older homes commonly have 10 to 15 ACH50; newer homes may have 5 to 10 ACH50; homes built for low air leakage range from 1 to 3 ACH50. By comparison, the Swedish standard for new single-family homes is 0.5 ACH50. The Canadian program for energy-efficient new residential construction has a maximum leakage standard of 1.5 ACH50.

To conduct a blower door test, technicians close all openings within the heated area of the house. They then seal a special, powerful fan within an exterior-door opening. The fan pulls air from the house. Gauges measure the difference between indoor and outdoor air pressures, as well as the air flow through the fan. The technicians adjust the fan to maintain a constant pressure differential and take readings, which they use to calculate the leakage rate.

During the test, outdoor pressure forces air through openings in the building envelope. It is easy to feel these leaks with bare hands. The technicians may also use squeeze bottles containing a chemical that combines with air to produce a puff of smoke. Leaks are unmistakable. The technicians record the exact locations of problem areas and give a report to the homeowner. This report will be very useful in the next stage of the process.

The homeowner or contractor seals the identified leaks with materials that include foam, acrylic adhesive tape commonly used to tape air barriers, acoustical sealant, polyurethane caulk, polyethylene sheet, and rigid foam.

The final phase is verification. After leaks are sealed, the blower door test can be repeated to measure improvement on the airtightness of the home. It may point out an area or two that needs more sealing, or it may confirm that the job has been done well.

The blower door test is a proven, objective means to identify air leaks in a home. It removes the guesswork of weatherizing and improving a building’s efficiency and comfort. Thus it is an invaluable ally to both homeowners and contractors.