gap under door for return air

[John Dirks Jr]

Consider a house with central returns. In the upstairs bedrooms, is 1/2 inch enough gap under the closed door to allow sufficient space for return air to get out? The registers are standard size.

[StevenT]

Consider a house with central returns. In the upstairs bedrooms, is 1/2 inch enough gap under the closed door to allow sufficient space for return air to get out? The registers are standard size.

IMHO I think that any room, especially a bedroom, where the return air capacity/ventilation is dependant upon a 1/2" x 34" space under a door, is suffocating. The easier the return the better the output. Under the door is understood. There should be returns on the ceiling.

[Brandon Whitmore]

My buddies heating contractor says no. My friend just had a system installed in his new house--- there's jumpers installed throughout.

Small gaps beneath doors is the standard around here.

You'll know the answer when you see or feel doors sucking shut in a house.

[StevenT]

OK, but how well does itwork? If its sucking the doors shut that the system is working harder to return the air. Don't you think for a system to work optimally, it should balanced, favoring easier input. In tall building it called "chimney effect."

[Rocon]

Consider a house with central returns. In the upstairs bedrooms, is 1/2 inch enough gap under the closed door to allow sufficient space for return air to get out? The registers are standard size.

There should be returns on the ceiling.

The clearance under the doors is inadequate.

Wow, why would you put return air on the ceiling? That seems to be the best way to short circuit the conditioned air in the heat cycle. I would never put a return on the ceiling in a residential unit.

I had a set of condos that the HVAC guys installed the return near the ceiling. The thermostat was in the work area, and by the time the heat would get comfortable in the work area the loft was over 90 degrees. I made them change out to a return at floor of work area and suddenly the whole unit was comfortable.

I bought a home that had a ceiling mounted return in the basement as well as a floor mounted return on the ground floor. The basement was always cold summer and winter. I moved the return in the basement to the floor level and again suddenly the home was comfortable year round.

[hausdok]

Hi,

I'll venture a guess that at least 90% of the new homes built around here over the past couple of decades have exactly that configuration and don't have any problems. The location of returns and the method of return isn't something we decide or design - it's something decided by the guy that installs the system. I think that it would be fair for a home inspector to call out a return intake located too close to a furnace or undersized intake openings at the walls; but I think it's notour call to decide how high that gap under the door must be - that's pretty much decided by the designer and the code guys.

I don't understand why so many folks want to play at engineer. The job is about observation and reporting; not in-depth technical analysis.

ONE TEAM - ONE FIGHT!!!

Mike

[RobC]

Hi John,

That's an absolutely GREAT question.

Here is a basic calculation I use to answer the very same question I have about basement development returns etc.

A regular register is usually 3" x 10" or 30 sq inches in area

Assuming you have only one register in the bedroom, then you'll need the same area for return.

So, if the door is 30" with 1/2" space then you have 15 sq inches or half the requirement.

You can do the same thing for homeowner basement developments if you have such a thing. Add up all the registers X 30 inches and that's what you need for the return.

[John Dirks Jr]

The report went out before I got a response to this thread. Basically, I was inquiring for future reference.

For the record, I did not write up the upstairs rooms with 1/2 inch gap at the door bottoms.

I did write up the basement rooms where the doors were snug to the carpet.

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[charlieb]

OK, but how well does itwork? If its sucking the doors shut that the system is working harder to return the air. Don't you think for a system to work optimally, it should balanced, favoring easier input. In tall building it called "chimney effect."

I comment when the door pull shut/offer any resistance to opening. I call it a symptom. I don't specify repairs.

[StevenT]

The clearance under the doors is inadequate.

Wow, why would you put return air on the ceiling? That seems to be the best way to short circuit the conditioned air in the heat cycle. I would never put a return on the ceiling in a residential unit.

When cooling, the convection makes the system work a bit easier.

Easier=better.

I agree, it would not be helpful to the heating cycle.

Maybe it's a regional thing, around here, most homes have high/higher returns. some have sepatate systems and have both.

So I guess, where and how you place the returns, has alot to do with the site. If all of the returns were low, and the problem was cooling, would you raise the return?

[StevenT]

OK, but how well does itwork? If its sucking the doors shut that the system is working harder to return the air. Don't you think for a system to work optimally, it should balanced, favoring easier input. In tall building it called "chimney effect."

I comment when the door pull shut/offer any resistance to opening. I call it a symptom. I don't specify repairs.

I agree, it is a symptom. Just like any other symptom, I would report it. If it is a symptom that has an effect, I recommend having it repaired, replaced or serviced. I don't make a habit of deferring.

If my client wishes, I am willing to do discuss different options. Do I specify repairs? Only EIFS.

[Rocon]

The clearance under the doors is inadequate.

Wow, why would you put return air on the ceiling? That seems to be the best way to short circuit the conditioned air in the heat cycle. I would never put a return on the ceiling in a residential unit.

When cooling, the convection makes the system work a bit easier.

Easier=better.

I agree, it would not be helpful to the heating cycle.

Maybe it's a regional thing, around here, most homes have high/higher returns. some have sepatate systems and have both.

So I guess, where and how you place the returns, has alot to do with the site. If all of the returns were low, and the problem was cooling, would you raise the return?

Actually the basement condition I described had an additional result. The basement was not as cold during the cooling cycle. The basement was near 60 degrees during the cooling cycle before and 70 degrees after when the thermostat was set to 72. I believe (but have no empirical data) the HVAC did work less since for the most part the temperature differential was narrower finding a thermal equilibrium. The basement being below grade was sort of a thermal well that was not used initially to cool the house.

To clarify my previous comment about the gap being inadequate. Many homes have supply to a bedroom with no return. The gap at the bottom of the door is forced to serve the return function. This is why we see dark stripes under the door caused by impaction. As a carpenter I always set the bottoms of doors 3/4" higher than finished floor height. I noticed that this allowed air to equalize when the door was opened and closed.

I also agree that there are differences between regions in what is minimally acceptable or generally accepted. I see that all the time in the southwest, contractors do not worry about making the buildings water or air tight. Where I started building if something was wrong you had one freeze thaw cycle and you knew it was an issue. In CA you could have an issue that does not appear for a couple of years. That is the gray line between design specs or optimal performance and something working for the most part.

I think John's write up was correct. He stayed away from hypothesizing.