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.
You’re not getting the airflow you think you’re getting
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.
Get building science and energy efficiency advice, plus special offers, in your inbox.