Garbage bags can be pretty handy components of an HVAC contractor’s tool kit, research in 2003 at Lawrence Berkeley National Laboratory (LBNL) (see “Air Flow Measurements in the Bag,”HE Sept/Oct ‘02 p. 8).Toting around a laundry basket is also a good idea. Indeed, contractors can often diagnose HVAC system pressures more accurately by using these common household objects than they can using commercially available flow hoods.

We researched the use of garbage bags as a measurement tool for two main reasons. First, bag filling has the advantage that it gives a direct volumetric flow without relying on flow measurement techniques that only sample part of the flow or assume a degree of flow uniformity, as almost all of the other techniques do. Second, as a demonstration of high or low flows to homeowners—or builders and HVAC contractors—bag filling has a direct visual element that is
very appealing.

See: "Garbage Bags and Laundry Baskets" by Iain Walker, Home Energy, Nov/Dec, 2003