Defining Blower Door and Infiltration Testing
This is our favorite topic at Wilson Services, Inc. Why? Because infiltration is so incredibly misunderstood. When we say misunderstood, please don’t misunderstand; we acknowledge that the term blower door is not a main stream word for the average home owner. What’s so amazingly misunderstood is that there are many heating experts, news paper column writers, and energy experts that have completely missed the boat.
A blower door is a mechanical piece of equipment that temporarily occupies an outside door of your home. It takes about 5 minutes to set up the equipment. Once the house is prepared (takes a few minutes usually), the fan is turned on and the operator will ramp up the speed until we reach a certain level of negative pressure in the home, usually 25 to 50 pascals.
Lets begin with some fundamental information that doesn’t take a lot of building knowledge to understand. Our Massachusetts homes and businesses lose heat in the winter months because of heat loss. Just like you need a coat in cold weather (your body loses heat faster when its really cold out), the same holds true for buildings. Simply stated: the colder it is outdoors, the faster your house will lose heat.
There are several basic elements to heat loss: the exposed surface area of the walls, ceilings and floors (and the associated R-value), the glass (you may see the term glazing on manual J programs), and the infiltration (you may see the term air change per hour). Infiltration directly relates to how leaky or tight the home is. The calculation is dependant on the total volume of the home (high or vaulted ceilings?). There is also ventilation to consider, but that’s a different subject.
So, now that we have some basics down, why all the fuss? Where is 95% of the world going wrong when it comes to how leaky your home is? It has to do with the idea that, in general terms, not all of the leaks are coming from doors and windows. Its also coming from the basement and the attic as well. Yet, everything we read instructs us to seal up the leaky windows and doors. There is a big problem with that teaching.
The average house will breathe on its own. Its a law of physics. Otherwise, wed be living in submarines. Now, if we go buy a dozen tubes of caulk and spend the weekend squirting silicone into all the gaps at the window framing, did we slow down the infiltration? You bet! Is our house tighter? Sure is! Is it healthier? Probably not! Is it safer? Probably not!
In our example, we just plugged up the good air entering our homes. Now granted, some houses are so leaky they could stand the example were laying out here, and perhaps still be much too leaky. That’s not the idea here (to cover every possible scenario), nor does (hopefully) anyone reading this expect that.
We have to get technical here for a moment. The fact is, when we slow down the infiltration at the windows and doors, we hasten the infiltration at other areas of the house. Unless you’re familiar with all the methods that trades people utilize to build your house, you may not realize how many breaches there are between your living space and the air in the basement and attic, and other unsuspecting areas like knee-walls and bonus room challenges. What were spelling out here is that while you may have just cut your energy bill down some, the overall comfort and health may have went backwards. Breathing outdoor air is good; breathing attic and basement air is not. Remember when Katrina had caused damage to the dykes in New Orleans? The workers frantically tried plugging holes, yet when they repaired one breach the added velocity of the flood water created even more abusive destruction at other areas of the dyke. It was a fight against Mother Nature. The same is true for our homes. When we plug up the good air, its possible (or likely, too many factors for us to choose a word here) that bad air will take its place.
Home energy experts (the real ones that is) are very familiar with atmospheric combustion appliances (your heating and hot water for example), and the negative impact tightening up a home will have on these appliances. The areas where these appliances reside (usually basement in our part of the world) is referred to as the CAZ, or the Combustion Air Zone. If we mess around with the CAZs ability to get the needed air to the appliances, we now have a problem on our hands. It may go unnoticed, or it may be so noticeable all your neighbors will get the hint when they see big red trucks zooming down the street to your house with sirens on.
The blower door will give us much needed information as to exactly how much air in entering the home. It will tell us if the home is too leaky, too tight, or just right. Just because you have a newer home, don’t be fooled into thinking your home is tight. We have tested many newer homes and walked out with dismal infiltration reports. Even nicer communities like Amherst Woods have homes that are well below industry standards