Allison Bailes takes up the age-old debate about undercutting bedroom doors to provide adequate airflow back to the home's return air grate. It starts here:
Door undercuts typically won't allow enough air to get out of the bedroom unless you leave a gap bigger than most people want under their doors.
Which is not bad advice. Building Science Corp. and the Florida Solar Energy Center, two stalwart building-science sources lend support to the idea that door undercuts as return air pathways rarely work.
Still, a lot of HVAC contractors will dispute this, in part because installing an adequate jump duct or transfer grille is a lot more mess and expense than they are often willing to upsell to homeowners.
And while many HVAC installers are leaning only on "conventional wisdom," Bailes is persuaded by John Semmelhack, a well-respected building science consultant whose work supports the idea that many door undercuts actually do work ... or more precisely, the door undercuts and air leakage under the door can provide adequate airflow (the same amount that FSEC says is needed).
It's worth reading this blog to be sure you understand all the twists and turns, and most importantly, where they all lead. In the end, the discussion is a long-winded, but imminently readable argument for actually measuring the performance of each HVAC install - the process of commissioning that Allison (and many other respected building-science consultants) advocate.
