What does having a low ACH (Air Change Per Hour) mean for you?
-You can reduce energy consumption due to air leakage.
-You can avoid moisture condensation problems.
-You can avoid uncomfortable drafts caused by cold air leaking in from the outdoors.
-You can save up to 30% on your energy bill just by making necessary upgrades following a home energy assessment.
The current Georgia building code requires a new home to have a air tightness test performed and be at 7 ACH or lower to receive a Certificate of Occupancy (C/O). This same code also requires duck tightness testing under certain circumstances but this article will discuss the air tightness only.
To measure the amount of air leakage in a home we use a tool called a blower door and a manometer which measures pressure. Let’s first start off by talking a little bit about what a blower door is. A blower door is a powerful fan that mounts into the frame of an exterior door. The fan pulls air out of the home lowering the air pressure inside. The higher outside air pressure then flows in through all the unsealed cracks and openings.
Blower door tests are done to find the air infiltration rate of a building to determine how airtight your home is and to help find leaks. In addition to finding air infiltration a blower door test can also help find defects especially in conjunction with an infrared camera. The blower door will intensify the natural infiltration occurring in a house while the air outside that is forcing its way in shows up as a different color on the infrared camera. There are two types of blower doors calibrated and uncalibrated. It is important that when testing you use a calibrated door. The calibrated blower door has several gauges that measure the amount of air pulled out of the house by the fan. Uncalibrated blower doors can only locate leaks in homes and they provide no method for determining the overall tightness of a building. The calibrated blower door’s data allows the auditor to quantify the amount of air leakage and the effectiveness of any air-sealing job.
Blower door results can be expressed in a few different metrics. The most common one is air changes per hour (ACH), or how many times a house’s air is completely replaced in a given hour. Because we take our blower door measurement at 50 Pascal, most codes and standards reference the air changes at that elevated pressure, but we can also calculate the air changes under natural conditions as well. For example a code-built new home with decent air sealing might have 7 air changes per hour at 50 Pascal that means if we kept the blower door running for an hour it would pump in enough air to completely replace the home’s air 7 times. The math and metrics can get a little bit complicated so let’s put them in context. Here is a rough scale to compare your blower door test number to other standards: 10-20 ACH50 – Older homes with almost no air sealing 7-10 ACH50 – Average new home with some air sealing 7 ACH50 – OK infiltration level and the 2009 IECC energy code requirement 3-5 ACH50 – Good and achievable target for most new homes. 3 ACH50 and lower – Tight home with great air sealing, and required by the 2012 energy code first adopted in MD and coming to other jurisdictions soon. .6 ACH50 – Super tight home and the Passive House standard.
Preparing for testing:
– If you heat with wood be sure all fires are completely out this also includes hot coals before the auditor arrives.
– Remove any ashes from open fireplaces.
– Plan for a walk through of your home with the auditor.
– Be prepared to point out areas that you know are drafty.
– Expect the auditor to request access to all areas of your home this can include closets, built-in cabinets, attics, crawl spaces, and any unused rooms.
– Expect the auditor to set controls on all fossil fuel appliances to ensure that they do not fire during the test. This can include stoves, water heaters, etc.
– Expect the test to take up to an hour or more depending on the complexity of your home.
C&H Construction is a licensed general contractor and Custom Home Builder located in Blairsville,Union County Georgia serving Towns County Georgia, Fannin County Georgia, Gilmer County Georgia and the North Georgia Mountains is certified in air tightness testing.