Variable speed fans are used for air tightness testing. In order reach flow values as high as 6,000 cubic feet per minute (cfm) and as low as 20 cfm, restricting rings are added to the opening of the fan. As a ring is attached, the pressure measured across the fan is different for corresponding flow values. Select digital pressure gauges have all of the correlating values of pressure differential to flow embedded in the gauge. However, the gauge can’t see which ring is placed on the fan or even if there is a ring. When the ring and fan selection indicated on your digital pressure gauge does not match the ring and fan you’re using for a house test, it can result in inconsistent air tightness values for a house. If the flow value you receive is unusually high or low, it is best to look at the space you are testing as a whole, and compare the size of the house to the test you are performing. A rule of thumb is a moderately constructed house will have about 1 cfm of leakage per square foot. In other words, a house with 1,000 square feet of living space being tested will measure around 1,000 cfm.

Tip #2: Trim tubing each month for an airtight connection between the fan and gauge.

Air flow is generated through an opening when there is a difference in the pressure from one side of an opening to the other. With air tightness testing, the fan generates difference from one side of the door to the other. To transmit that difference, tubing is connected from the outside to the pressure gauge as well as from the fan to the gauge. 

When you repeatedly attach and detach tubing from pressure taps of the pressure gauge or the fan, it can cause tiny tears at the end of the tubing. This results in air leakage at the connection and can lead to issues such as your digital pressure gauge showing Lo on a larger ring, while it can’t reach 50 cfm on a smaller ring. To prevent inaccurate readings, make sure there are no leaks in the tubing leading from the fan to the gauge or from the flow sensor of the fan to the gauge. Check your tubing on a monthly basis for leaks, and if needed, trim the ends of the tubing to give it a clean connection. The simplest way to check tubing for leaks is to plug one end of the tube with your finger, and suck on the other end to see whether it sticks to your tongue. If it sticks to your tongue, the tubing is airtight. If it does not stick to your tongue, then it’s time for a trim.

Tip #3: Remember to add a pressure tube when switching from a depressurization test to a pressurization test.

House and duct air tightness testing can be performed as pressurization, adding airflow with the fan, so that air moves through the various building components and moves to the outside. Conversely, a depressurization test can be performed, moving air out of the house so that air moves from the outside and then through the various building components. In general, there is little difference in the actual value between a pressurization test and depressurization test. The critical difference in the test with regards to a house test is to have the fan referenced to the inside. With depressurization the fan sensor is already in the house. For a pressurization test the fan sensor is outside.

When an energy rater or compliance tester switches to a pressurization test, it is common to forget to add the extra pressure tube needed. Without this additional pressure tube, a pressurization test will show inaccurate readings. To ensure your air tightness tests are accurate, remember to add that additional pressure tube for pressurization tests. Energy raters can get assistance with connecting proper tubing for each type of air tightness test by using an advanced digital pressure gauge that guides them through the steps of a test.

The No. 1 goal of energy raters is consistently accurate test results; however, it’s understandable that performing air tightness tests can be a complicated process. Using the three tips in this article will help you avoid the most common, preventable problems energy raters encounter.

Frank Spevak, marketing and sales manager for The Energy Conservatory, has more than 30 years of experience in the HVACR industry with expertise in air and pressure measurement equipment. For more information, visit www.energyconservatory.com.

Publication date: 12/7/2015