Comments on: Can Door Undercuts Work As Return Air Pathways?

By: Deniz Erkan

Deniz Erkan — Mon, 29 Jun 2020 18:42:54 +0000

I've got a bedroom door that
I've got a bedroom door that closes itself when the air is running and it's already less than a foot agape. I've got another door that slams shut (obviously none that swing open). Not owning a manometer, how does this correlate to 3Pa vs 7Pa difference ?

By: Deniz Erkan

Deniz Erkan — Mon, 29 Jun 2020 18:21:08 +0000

In reply to abailes. Having lived in Europe, I
Having lived in Europe, I used to assume the purpose of door undercuts was childproofing-related: 1. Large enough to slide the room key underneath, because bedroom doors used to have individual keys 2. Large enough to pass a sandwich to my child who locked himself in, while waiting for alternative ways to get the door unlocked

By: carlos

carlos — Fri, 05 Jun 2020 19:26:27 +0000

What un-expensive tool can be
What un-expensive tool can be used to be able to measure pressures between rooms?

By: chuck halloran

chuck halloran — Fri, 22 Nov 2019 15:31:16 +0000

Jonathon,
Jonathon, You offer not solution other than all other replies which do as idiotic? You state the reason for having a room is to block out light and noise. I agree to this on a technical level, however, I would suggest the primary reason is comfort. Those irritant you refer to are little league matters. Noise and light are easily over come. A 8X8 grill or hallway noise sneaking into or out off are superficial at best. But, If a person is to Hot or to Cold due to their human comfort then you have a permanent because someone is blocking the path of correct airflow.

By: Jonathan

Jonathan — Fri, 22 Nov 2019 11:53:18 +0000

I dry walled right over all
I dry walled right over all of the vents above the doors of the bedrooms in this new house. They completely defeat the primary function of a room which is to block light and noise from entering. What purpose is there to having a room at all if there’s a giant vent letting all sound right through it?! May as well just not have doors. It’s the dumbest thing I’ve ever seen and there hasn’t been a single problem with the vents gone. The doors don’t slam, the rooms don’t feel any different than before, there’s no issues. If you’re designing a new house and you want to nerd it up over pressure differentials that nobody else cares about, at least do it the right way and use jump ducts or some manner of preventing sound from traveling room to room. Short of that we’d all need our own houses on the same block to live with anyone else. So idiotic.

By: David Butler

David Butler — Wed, 24 Jul 2019 19:00:34 +0000

In reply to Richard Gunkel. @Richard, I've seen
@Richard, I've seen guidelines (aka rules of thumb) for how much airflow a given size diffuser can or should have, but the reality is all over the map. So I don't recommend trying to size door undercutor transfer ductgrillebased on supply vent dimensions. In general, return paths should be sized based on room-by-room design airflow and field verified via zonal pressure testing. Anyone who operates a blower door or duct tester will have a digital manometer that can measure pressure differentials in the appropriate (i.e., minuscule) range. It only takes a few minutes. However, when testing indicates a problem, calculating the minimum return path to get to 3 Pascals requires an accurate flow hood to measure the actual supply airflow, which unfortunately is less common in the trade. Anyone who routinely does zonal pressure diagnostics should own a good flow hood, although I suspect trial-and-error is the status quo.

By: Richard Gunkel

Richard Gunkel — Tue, 23 Jul 2019 14:54:47 +0000

Could you calculate the
Could you calculate the return path vent size needed under the door by knowing the size of the vent in the room?

By: David Butler

David Butler — Tue, 30 Jan 2018 20:17:17 +0000

In reply to Thomas Dugan. Thomas wrote: "What I found
Thomas wrote: "What I found missing was any reference to what constitutes a "bedroom"? Don't we need to take into account the number of vents and flow into the space?" It's not the number of vents or the type of room but the design airflow for the room that determines the design return airflow. Also, it matters not if there's a dedicated return duct, or a passive return path to a central return as long as the return path isn't restrictive to the point that it impacts overall supply air balance.

By: Thomas Dugan

Thomas Dugan — Tue, 30 Jan 2018 14:45:51 +0000

As always, a great article.
As always, a great article. What I found missing was any reference to what constitutes a "bedroom"? Don't we need to take into account the number of vents and flow into the space? I had a problem experience with a home I built that the master bedroom was actually a master suite, consisting of a large sitting area, large walk-in closet, enclosed toilet space, and a long vanity with two sinks in addition to the area large enough for a king sized bed. There were six vents supplying this area. Their door would slam shut during the night. We had to find space for a large grill to vent into the hall. Not pretty but worked. We should have designed return vents in the ceiling or better yet, its own return duct. Lesson learned.

By: Neil Fimbel

Neil Fimbel — Tue, 30 Jan 2018 12:07:33 +0000

Thank You so much Allison for
Thank You so much Allison for this very important issue, living in Florida i deal with the hvac installers all the time on this undercut door subject, i typically tell the industry that about 30 cfm’s at best will exit trough the undercut when the door is closed (beds need on average 100 cfm)- many believe they are forced by the codes to add transfers (i hate transfers) or ducted return – they have little clue of the actual .001 engineering requirement. could we also now get a discussion about the manual T / D location for the return air pick up . see my link to paper about cooling dominant return air locations – transferring the warm moist column of air from a high wall transfer into an adjacent hall way is not the best solution (but at least we have the industry tuned to balanced return air) for a cooling dominant region as this transfer air is usually expected to be returned to a low wall return air grille in our region! pushing this air to an adjacent room is a poor choice. as most new homes require a ventilation air duct, there is also no way to balance the free draw low wall return and ventilation air duct because there is no plenum to place the volume control dampers – the path of least resistance wins every time, so no ventilation air is induced while using an open stand with a single low wall r/a……passes code official inspection every time…so our installers believe that if it passes inspection it must be engineered correctly! help Florida please, your highly respected by professional designers in our region despite FSEC missing that critical point on this subject —>white paper http://www.hvacdesigns.com/wp-content/uploads/2018/01/Ceiling-Return-Air-Grilles-for-Cooling-Dominant.pdf?bb83b9&bb83b9