Central AC and Closing Interior Doors

[mark_wpduet]

From the website:
Always keep all of the doors open when running central air conditioning. Central air runs off a blower fan and the system is balanced for whole-house cooling. Closing a door unbalances the system, causing pressure changes that suck hot air in from the outside and bleed cold air through leaky air ducts on the inside. Your central AC runs longer and works harder to compensate with these conditions when a door is closed.

Anyway - This leads me to this question. In my house, there is one door that we have to keep closed (it's a spare bedroom with stuff in there and the cat is not allowed in that room), but the rest of the doors are opened, except for the master bedroom closet. There is a vent in that closet, would that mean I need to keep that door open as well?

 

[yogitunes]

to a point, they are correct, and you would most likely have to keep that door open during the A/C setting....

as our unit in the country house is down on the far side of the basement, the other side doesn't get the full cooling effect, figuring on closing or tempering down rooms in order to force more air to the other side of the house....

the thing is, it threw my unit into havoc, run longer, and it would freeze up.....as the tech instructed, we opened everything back up, unit runs fine....

we could close bedroom doors at night, where the unit didn't run as much, just not something to do all day long...

I use to install those 3M Hepa filters, they worked well, but filled up fast, which slowed down air flow, this also caused the unit to freeze up....so those are saved for the winter months only......the regular blue ones work great if you spray them with Lemon Pledge or Pam cooking spray, and change them often as they will attract dust quickly....

 

[neptunebob]

But you shouldn't have to do that...

Each room in a house with forced air heat and AC should have both a supply grille and an return grille, except the bathrooms have just a supply to keep the odors away from the rest of the house. Closing door should not make any difference if there is properly installed ductwork.

 

[DADoES]

 
Typical design here is supply registers in each room (one or more depending on room size) and one central return in a hallway or some such ... not a return in each room.  Returns also depend somewhat on size and layout of the house.  I have one system, two returns -- one at each "leg" of the L-shape.

 

[appnut]

I have one air return right in the center of the house and only one air register per room.  One bedroom door stays closed most of the time because it tends to be the catch-all room. 

 

[launderess]

Responses pretty much nailed things down

Central (forced) eating or cooling for that matter in principle has not changed much since days of those huge old "Octopus" or whatever furnaces that sent hot air up into buildings. Things depend upon the free flow of air circulation. If or when that does not happen, often units can or will make their displeasure known.

Cannot say have ever seen a home or apartment with central heating and or air return registers in every room. Vents for incoming cool or hot air yes, but not other way round.

Now with through the wall or window AC, yes, you can (and maybe should) close doors to unused or whatever rooms to lessen the load. This or the opposite; use of fans to help move cooler air/improve circulation.

 

[yogitunes]

well, I do have return vents in all rooms except the bathroom, they are located up high....

my MIL has a unique setup, return vents in all rooms, but located at the ceiling and below at the floor, theres a tiny servo motor driven vent that controls where the air is pulled from......during the winter it pulls air from the floor level, during the Summer A/C mode, it pulls from the ceiling level...theres also a variable speed blower....

also a Dehumidify Mode, turning on both the heat and A/C...found this to be excellent on rainy days....

what I like too, is all levels are the same temp, keeping the basement area equal to the top floor

 

[launderess]

How interesting Yogi.

Did you add these return vents after system was installed, or did you plan things that way?

 

[washman]

FWIW

I only have 2 bedrooms however I have a supply vent in my master bathroom AND the walk in closet. I keep the doors open all year long.

 

The rest of the layout is "open floor plan" so the living room/dining/kitchen are pretty much all one area.

 

Bed 2 has 2 return air, master bed has 2 return air, hallway has 2 return air and in living area 2 large return air grills are supplied.

 

Needless to say, air circulation is quite robust with this setup.

 

[circlew]

The HVAC system in my house has return air intakes in all the bedrooms, and one large return in the hallway for the living and dining rooms.

Another thing is it depends on how many separate HVAC systems the house has. My cousins in TX lived in a house that had 5 units (it was a very large 2 story house), and they would close off the rooms upstairs, and keep them warmer in summer and cooler in winter if they weren't being used. Also, some systems are zoned with dampers.

I think it is a good idea to have the HVAC system tied into the fire, smoke & waterflow detectors, so that the air handler will shut off in case of fire. You can also get doors equipped with a release that will close them if the fire alarms are activated. This will drastically cut down on heat and smoke damage if a fire occurs.

 

[fan-of-fans]

I've noticed with a lot of newer houses, that the bedrooms have equalizer vents, either one above each door that lets the air pass through the wall back to the hallway, or one on the ceiling that is connected with a duct to another vent in the hallway.

This allows the air flow to be equalized when the doors are closed. Not sure if this is a code requirement or not. Hadn't really noticed it until the last 10 years or so, although I have seen the vents above doors in mobile homes further back.

The

 

[launderess]

Don't know if this applies to current conversation

But was brought up to always sleep with bedroom doors closed (and a window cracked open) as "in case of fire) or whatever.

If you notice in old films or other media people and even children/infants are always sleeping behind closed doors for most part. If that arrangement affected airflow from central heating/cooling then something would have to give one suspects.

 

[yogitunes]

no, all this stuff was already installed....just took a while to understand how it all worked...

remember homes and/or apartments that had sort of a vent window above the doors...the front door usually was frosted, with the number of the Apt/house....all interior rooms were clear glass, never knew how they tilted, just that some were open and others closed, never thought about how these would be used for temp adjustment per room...

 

[launderess]

Yes, recall those as well.

They are called transoms and at one time were very popular for indoor doors and or above entrances into apartments or whatever.

Idea behind transoms was in days before AC one could have closed doors (interior or otherwise), but still have ventilation. More so if you opened windows.

IIRC they are outlawed in New York and most other areas by code for new construction due to being a fire hazard. Well at leas the ones which open, fixed transoms are another thing. https://en.wikipedia.org/wiki/Transom_(architectural)

Ordinarily if a door is closed (and especially if it is fire proof) it will contain a fire and good amount of smoke on the other side. OTOH if the fire is elsewhere a closed door prevents smoke (which is the main killer in a fire) from getting into a room/apartment. Transoms obviously defeat that purpose if door is closed but they are not.

You can still find transoms in some of the older buildings here in NYC (and we have plenty). Some have been painted over and or sealed, others still work as intended. These would be above interior doors only. IIRC all such devices above doors that lead into apartments or offices have long since been sealed or removed (see above).

https://law.justia.com/codes/new-yo...inistrative-code-new/adc027-2044_27-2044.html

https://govt.westlaw.com/nycrr/Docu...ype=CategoryPageItem&contextData=(sc.Default)

https://www.quora.com/Why-dont-doors-have-transoms-anymore

 

[xraytech]

My central air has 1 supply vent in each of 3 main floor bedrooms, the bathroom, kitchen, and 2 in the living room.
I have 2 return air vents, 1 in living room and 1 in hallway.

All my doors are left open, except for door 2 second floor where there are no air vents. I close the bedroom door while sleeping, and the other bedroom gets closed when receiving company as it’s the catch all room.

 

[mark_wpduet]

My house

isn't very large. It's a single story 1375 sq ft 3 bedroom 2 baths. In the middle hall, there are two (I guess they're called intakes?) One on the wall and a smaller one on the ceiling. I keep the filters super clean. That's the only intakes in the entire house. I've never lived anywhere where there were intakes in each room of the house. But closing the master bedroom door definitely is less efficient, at least during the worst parts of the day, especially if it's full sun out. It doesn't seem to matter during the night where there's no sun at all.

On very hot/humid full sun days, my AC will maintain 71, possibly jumping up to 73 if it gets past the mid-90s F. But let me close that master bedroom door during that part of the day and you can feel the house slowly warming and the Tstat will jump up as well.

 

[tolivac]

My house has two intakes in the hallway-no intakes in the rooms.Never seen that in a house-do see it in commercial office buildings.My old Lennox still chugs along!I leave all the doors open-gives best efficiency with a central system.

 

[askolover]

My house, MIL's house, parents' house, best friends house all only have one air return in the hallway.

 

[revvinkevin]

Interesting.

 

 

I had never heard of having an air "return" in each room, at least not in a residential setting anyway.

 

I did see equalizer vents between rooms in a few homes some years ago, thinking that was odd back then because I didn't get the purpose.  Now I get it.

 

My house is just under 2200 sq ft, all on one level.  When I had the central HVAC installed, I had them install two supply vents in the master bedroom rather than one, being it's a larger room with a 12 foot vaulted ceiling.   For the air returns, they wanted to put one really large one in the hallway near the bedrooms, but I asked them to split it into two and put another one towards the front of the house as well.  The idea being the HVAC would draw in return air from each end of the house. 

 

I have always slept with interior doors open, but my other half isn't comfortable with that, so now they're all closed at night.   Being there is so much air flow to the bedroom, with the running the A/C at night, I'll prop the door open 5-6 inches, with something on each side of the door so it won't move.  If I don't do that, will slam the door shut when the A/C comes on.  Obviously this can be unnerving if you're sleeping or nearly asleep.   

 

Otherwise I keep the registers and doors closed for rooms that are rarely used in an effort to reduce cooling load and costs.