Room size requirement for HVAC supply

Was wondering what the basic size requirement is for a room to have a HVAC supply vent. Have run into several powder rooms lately that are not supplied, but I think probably should be. Did some superficial research and didn’t find this. Is there a rule that one of you HVAC experts could give out. Either max SF not requiring HVAC supply or minimum SF requiring HVAC supply.


I know of no rule that states a specific room size requirements.

Okla’s SOP does not include efficiency but common sense tells me that it should.

We nowdays install registers in walk in closets that never use to be.

As an inspector If I see an area that is not receiving conditioned air or is a hot spot I will make a comment in my narrative general section. I see poor duct design all of the time very common around here.

Just had one this week that the supply duct used 3 plenum’s in supplying air to the far side of the home. Very poor design

My thoughts were along those lines Charley.

My master closet, and most I see, are supplied, and my powder room is as well. Lately I am seeing alot of powder rooms in new construction with no supply. Thought I remmebered seeing something in reading one time about a size requirement - hence why the master closets were supplied.

I mention it in general in my report as well, was just hoping for some backup to help the client get action fromt he builder.


The guideline I use for a small area is if it has a door or not. If a powder room or other small room can be closed off but has no supply register, I will metion it in my report. Otherwise, I do what Charley does and report on a “hot spot” if one exists.