What’s a “faith-based ventilation system”? It’s a ventilation system installed by a contractor who never verifies the air flow rates after the equipment is installed.
So, will this type of ventilation system work? It’s hard to say — because no one measured anything.
At last month’s BuildingEnergy 16 conference in Boston, two ventilation experts — Terry Brennan and David White — gave a presentation titled “Moving Beyond Faith-Based Ventilation.” Brennan and White explained why new homes need mechanical ventilation systems, and shared important design principles underlying these systems. They ended their presentation by providing advice on (and a demonstration of) different ways to measure airflow.
Terry Brennan is a building scientist and a member of the ASHRAE 62.2 committee (the committee responsible for the residential ventilation standard). David White is a principal at Right Environments, a New York architectural firm, and an assistant professor at Parsons.
Most builders have no idea whether the ventilation equipment they install is working properly. Many builders assume, for example, that a bathroom exhaust fan rated at 110 cfm is moving 110 cfm of air. It almost certainly isn’t, as anyone who bothers to measure their fans’ performance soon learns.
A few years ago, GBA blogger Allison Bailes recounted the tale of a builder who installed nine bathroom exhaust fans, each rated at 110 cfm. While the builder assumed that each of these fans would be able to move at least 50 cfm — less than half of their rated airflow — it turned out that only five of the nine of the fans achieved that fairly modest goal. (One fan barely limped over the finish line — it was tested at 51 cfm.)
When tested, four of the nine fans — the ones moving between 30 and 46 cfm — were particularly pathetic.
What about a kitchen range hood fan rated at 400 cfm? At high…