Opening the Window on Ventilation Facts

As a metaphor, the open window conjures so much positive imagery; namely the connection with the outside world. Because most operable windows are human-sized, it’s usually a “one-on-one” intimate connection. So it’s not hard to imagine why we love the concept of open windows.  The open window, however, fails miserably as a dependable ventilation device and building professionals (read “architects”) need to understand why windows can’t ventilate reliably. They certainly won’t ventilate economically as Ontario moves to tax carbon.

Don’t get me wrong, I live in a tight neighborhood of semi-detached, century-old, Edwardian houses without Air Conditioning (I don’t recommend that either) and we rely on the centuries-old technology of “open windows.” At the very least, the open window ensures a connection with the neighbourhood and occasionally, the cooler night-time air brings in temporary relief along with a night-time sideshow. We hear intimate conversations of late-night lovers waltzing by, raccoons arguing over food scraps, and occasionally, the melodic, eerie voice of a neighbourhood chap who sings dreamy ballads as he walks. Top that all off with the morning chirps of cardinals and robins followed by a mess of starlings and your circadian rhythm stays in lock-step with the world around you.

The bad news is that often that cool air is laden with humidity and besides the animated street-life drifting in, we get dust and pollen. Lots of pollen. Pollen that could be easily filtered by a quality ERV’s pre-filter. The really bad news about open window ventilation is that it’s very inconsistent where a few rooms get over ventilated (3rd floor) and others get under ventilated (basement).

Ask any architect, and I do almost every time I give a technical talk, “How many glasses of water does a human need a day to stay healthy?” and almost universally, they respond with “8 cups of water per day!” Bravo, we have a baseline. The follow-up question however is always met with blank stares; “How many cubic feet per minute of fresh air does a human need to feel healthy?” The guesses are wild. The follow-up questions are “How long can you live without a glass of water?” followed by “How long can you live without fresh air?” So why the short-shrift on proper ventilation in architecture school?

Here’s a Pro Tip: The architect won’t be paying your monthly utility bills, so unless they’re Passive House enthusiasts, don’t rely on them for mechanical advice and stick to your guns. Repeat after me “I want a balanced ventilation system with heat recovery, that’s fully distributed.” Thankfully, in 2017, the heat recovery part will be law in Ontario under SB-12, but you still need to ask for good controls and a dedicated distribution system.