A blower door is a powerful fan that mounts into the frame of an exterior door. The fan pulls air out of the house, lowering the air pressure inside. The higher outside air pressure then flows in through all unsealed cracks and openings.
Air leakage can increase heating and cooling costs over 30% and contribute to comfort, health and safety problems. Finding hidden air leakage sites can be difficult without the use of a blower door. Blower doors have gauges which can measure the relative leakiness of a building.
One measure of a home’s leakage rate is air changes per hour (ACH), which estimates how many times in one hour the entire volume of air inside the building leaks to the outside. Leakier houses have higher ACH’s, therefore higher heating and cooling costs, and greater potential for moisture, comfort, and health problems.