Air Quality – Exhaust Fan Only Do Not Work

Exhaust Fan

Exhaust Fan

There. I said it. It just does not work. OK, it works sometimes.* But it does not work in tight building enclosures and certainly not in new houses, apartments, town houses and row houses. Basically in nothing new that we are building. Because it sucks—literally. I know we were here before (“Unintended Consequences Suck,” ASHRAE Journal, June 2013), but we have to come back and deal with it again. Why? As amazing as it seems,things have gotten worse and are going to get worse. But the good news is as they become intolerably bad, we will end up finally dealing with them. Not quite there yet, but almost.

This next part should be obvious—but is apparently not to some people and is quite acceptable to others. Exhaust-only ventilation leads to depressurization in houses, town houses and row houses constructed to meet the 2015 International Residential Code and significant depressurization in apartment construction that is constructed to meet the 2015 International Building Code. In single-family detached houses, this leads to contaminants being pulled from attached garages, especially in houses with bedrooms over garages. Contaminants are also pulled from under slabs—if radon was valuable we would mine it this way—and what better way to bring soil gas, herbicides and pesticides into a home? In row houses and town houses, exhaust-only ventilation leads to air being pulled from neighboring units as well as from attached garages and from under slabs.

In apartments exhaust-only ventilation leads to air being pulled from neighboring units and corridors. In apartment construction, the corridor issue is a smoke and fire issue. You would think this might be something we ought to care about? Well, we do. In a serious way. But from a “tightness” perspective, not from a pressure perspective. We are getting good at the compartmentalization part, especially because we now test for it. But the compartmentalization makes the pressure issue way worse when we use exhaust-only ventilation. Read on…….

Excert Source: Joseph W. Lstiburek, PHD Ashrae Journal August 2016

Air Quality Exhaust Fan