The Top Sash Test Wondering Does my house have large bypasses exhausting a lot of heated air into the attic? Preparing 1. Wait for a calm, cold day. 2. Turn off the all the exhausts and blowers. 3. Take off any curtains or blinds on the test window. Testing Find a convenient window at the highest level of the house and slide the top sash down about an inch. (You can do this test with a casement, awning, or sliding window too.) Notice the direction of the air movement and gage the flow. Smoke may help you to see the flow of air. Analyzing Gravity will always make the warm air within a house press against the top of the thermal envelope. So an open window near the top of the heated space should blow out. As the stack of warm air under the window gets higher and the outside air gets colder, air will blow out faster. What happens if the window sucks in air? The house has a large air flow into the attic. The effect of this gravity driven exhaust is so great that entire house is depressurized. That's bad. Sealing the bypasses to the attic will stop this exhaust. As the air barrier gets tighter, the negative pressure in the house diminishes. The top windows will blow out and with more air sealing, lower windows will start to blow out. This is a very good thing. |