If your house has an exhaust-only ventilation system, does it need passive air inlets — that is, holes in the wall to let in outdoor air? In most cases, the answer is no. Unless your house is very, very tight — close to the Passivhaus standard of 0.6 ach50 — your building’s envelope is almost certainly leaky enough to allow for the smooth operation of a bathroom exhaust fan rated at 50 cfm or 100 cfm.
What’s wrong with passive air inlets? As I wrote in my 2009 article, Designing a Good Ventilation System, these aren’t “smart holes.” They’re just holes — and they’re just as likely to let air escape from a house as they are to let air in. The forces determining whether air enters or leaves these passive air inlets (also known as trickle vents) are the stack effect and wind, not the operation of a bathroom exhaust fan.
These facts were recently confirmed by Sean Maxwell in an article called “Ventilation: The Only Way That Passive Vents Will Work” (Home Energy magazine, January / February 2016). Maxwell formerly worked as a senior energy consultant at Steven Winter Associates in Norwalk, Connecticut; he now lives in Australia.
In his article, Maxwell describes the results of a research project he was involved with that looked into the efficacy of passive air inlets in multifamily apartment buildings in the U.S. Maxwell is one of three authors of the report, “Evaluation of Ventilation Strategies in New Construction Multifamily Buildings,” describing the research project. (His co-authors were David Berger and Marc Zuluaga.) The research was funded by the National Renewable Energy Laboratory as part of the Building America program.
While the researchers focused on apartments in multifamily buildings, many of their conclusions…