The air sealing task is more technical than most people suppose. Without the proper building science background it is really easy to cause problems. And, without the right equipment it is really hard to pinpoint the leaks and verify that you have actually accomplished the air sealing task.
Indoor Air Quality
Air sealing can have a significantly negative impact on indoor air quality. For example, if air sealing begins at the lower levels of the house, and the ceiling is left with significant amounts of leakage, a negative pressure (with respect to the outside) can be created at the lower levels of the house. Warm air is buoyant and rises to the highest point in the home. As it escapes out the ceiling, air is drawn in at the lower levels. As the house is tightened at the bottom, the house seeks out the path of least resistance. If this happens to be the furnace flue, air will be drawn down the flue—pulling the combustion gases (carbon monoxide) with it. Carbon monoxide detectors only detect large amounts of carbon monoxide and often times will not detect these lower levels. Over time, this low level of carbon monoxide can result in chronic health problems, loss of focus, and loss of short term memory.
Other indoor air quality concerns include: 1) Is there enough ventilation? 2) Is there enough combustion air? 3) When fans come on, is the combustion appliance zone under too great of a negative pressure? 4) Are negative pressures causing soil gases (radon) to be drawn up into the home?
Quantification and Efficiency
By using the blower door we can make sure that we are actually accomplishing our goals. We begin by measuring the total leakage in the home—expressed in CFM (cubic feet per minute) of air that leaves the home when the home placed under 50 pascals of negative pressure (more simply, the amount of pressure that the fan places on the home as it removes air). Next, we calculate a baseline CFM rate that is safe for your home. Then we set an air leakage reduction goal. If you are participating in the AHFC home energy rebate program, the goal will be set based upon how many steps we are trying to raise your home. Then we use the blower door to get an idea where which zones most of the leakage is coming from (i.e., garage, attic, crawl space, basement, master bedroom). The infrared camera is used to help pinpoint leakage areas. We start sealing at the top of the house and work our way down, focusing on the areas we found during our testing. Periodically we run a new leakage test to see how our work is affecting the leakage rate. After we have accomplished our goal, we run a worst case depressurization test—e.g., we turn all of the fans on and make sure that the furnace, boiler, and water heater and not under too great of a negative pressure.
This diagnostic process allows us to be very efficient, precise, and most important—safe.