The Meaning of ASHRAE 62.2

I have been a member of the ASHRAE 62.2 committee (the committee that establishes residential ventilation rates) for more than 15 years, but I just came to a simple understanding the other day when I was putting together a course for some wonderful weatherization folks in Pennsylvania. I don’t want you to laugh, because it seems so obvious, but it has taken me all this time to wrap my head around the meaning of the national ventilation standard. I mean there is so much fiddle-dee-dee stuff in there, it is hard to clearly see what it is all about.

It’s simple really: houses require whole dwelling ventilation.

Well, duh, you say. But it’s basic message, like many things in life, is clouded by all the ‘what-ifs’ and ‘where-fors’ and figuring things out in quadrature and a lot of fancy, scienterrific words. No, but seriously: all the air in the house is going to change naturally via cracks and holes and gaps and the wind and static pressure. Or it’s going to change mechanically because we’ve added fans, air handlers, range hoods, clothes dryers, furnaces, and water heaters. The complexities of the ASHRAE standard come from figuring out how many air changes we are going to need in order not to die because the house is too tight.

Houses are boxes of air. We have trapped a very small portion of all the air on the surface of our planet in the box that we call home. We don’t want to rebreathe the same air today that we breathed yesterday. Especially if someone is sick in the house – someone with COVID-19.

I want to point out that there is enormous amount of information – both good and bad – floating around out there about air change rates. When you see a number like 3 air changes per hour (3 ACH) that means that ALL the air in the house changes 3 times per hour! That is a huge amount of air to recondition every hour. In cold weather, that’s going to suck on your heating bill. You’re going to be wearing three sweaters and four hats. 3 ACH would be okay in a commercial building or a school. But it’s way too much for a house. What you might want in house would be 0.35 ACH or less.

So that’s what ASHRAE 62.2 is all about. It would be nice if the simple heart of things would not take 15 years to understand. We tend to obfuscate the meaning of life with folderol.