The Undercut and the Airflow

Spring is here, and in Phoenix, that means closing our windows and turning the air conditioner on. That means now is the time to talk about the airflow in your home.

Since school will be out soon, and the kids will be home, it’s essential to understand how the airflow in your home works, mainly if you have a teenager or budding teenager, who has strategically locked themselves in their room.

Well, that closed door has a small crack underneath it, doesn’t it? Let’s digress on that crack for a moment.


The undercut

The crack is known as the door undercut. The door undercut has long been a tool for small children to make a social connection with their mothers, in particular,  mothers who are in the bathroom. Whether it’s tiny, wriggling fingers, toys or other small objects shoved beneath the door, or, with the little head bent to be heard, their lips to the crack to murmur a tentative, “Mommy? What are you doing in there?”

What does the door undercut have to do with an HVAC? It’s crucial, as it turns out.

The cycle

Consider the cycle of air in your home for a moment. Starting at the filter, the air makes its way through the air return grill and filter, where it is warmed or cooled and blown through the ducts and registers. Some of that air flows into your teen’s room and stops, because the supplied air flow hits the closed door, substantially cutting off the return air flow. The primary way for the air to escape is from the door undercut, and if there is carpeting in the teen’s room, it may be inhibiting the circulation by slowing the returning air.


The airflow

Good air flow involves uninhibited air circulation. A closed door isn’t conducive to uninhibited air flow, which can create pockets of uneven temperature in the home. Poor air circulation can create a stagnant air odor and promote poor air quality in your home. Since people need fresh air to maintain health, poor air circulation can promote allergies and respiratory issues.

The door grille

A door grille solves the privacy issue and still allows airflow.

A door grille solves the privacy issue and still allows airflow.

While we aren’t telling you to pry your kid’s door open, it will help you understand if your HVAC suddenly isn’t performing optimally.  It’s correctable with a wall grille or door grille. They come in a vast range of sizes, styles, colors, and materials. Placement of a wall or door grille in rooms where the size of the door undercut is inadequate can improve airflow remarkably. If the occupant wants to have their door closed, they can do so without inhibiting the air flow to other rooms in the home.


Whether or not the undercuts in your home are adequate depends on a number of factors. We know that cold air will force itself out of the room in some other ways, including the sides and top of the door.  The problem is when a home seems to have odd spots of reduced air flow. If you have concerns about the circulation in your home, an HVAC expert can help diagnose and correct air flow issues.

Call us at King Plumbing, Heating & A/C if you need plumbing installation, plumbing repairs, rooter services or AC and heating service in the Phoenix Valley area at 480-907-0226.