Adding a return vent to a hot office

Question

I have an office with a significant amount of computer equipment in it that generates quite a bit of heat and is regularly 3-12 degrees warmer than the rest of the house when I'm working in there with the doors closed. (My house is a pretty large 5-bedroom house, so I'm not too worried about this affecting any large-scale balance.) Unfortunately, this room has no air intake vent. It does have a register from the HVAC. The room regulates its temperature fairly well with the doors open and I can feel a draft blowing out through the cracks in the doors when they're closed, so I think an air return is needed.

It's a squarish room with the HVAC register (4" x 10") under the window on the floor and the doors are on the opposite side of the room next to an air retrun vent in the hallway (it's quite close to the furnace and seems like a rather large cavity, not a long run so minimal friction). I've added a (bad) drawing of my office and what's on the outside walls. There is a basement below and a bedroom above this office, so neither the ceiling nor floor are really accessible.

Office Layout (the office is surrounded by black lines, the grey lines just show the outside rooms/areas, red show existing HVAC things):

Other than right around the door area, most of the walls are fairly off-limits due to what's on the other side (obviously not punching a hole into the garage, the bathroom is already too small, not making it smaller, and don't want to add anything to the foyer area for aesthetic reasons). I think the two areas that provide the most opportunity for adding an air return vent are either tapping directly into the air return cavity (shared with the hallway) or just opening up a new return pseudo-duct over the doors from the office to the hallway.

My concerns (I'm an engineer but no HVAC guy):

1. Because I largely want to remove heat year-round, I think the return vent should be on the wall near the ceiling (this is fortunate if I go over the door into the hall).
2. I'm concerned about noise transfer from the hall to the office or office to hall (I have a 3yr old, nuff said)
3. I'm not sure what HVAC codes & permits might be needed in this area of Indiana (Carmel). I think I might need a permit of some sort if I do HVAC duct work.
4. Something in my gut tells me I shouldn't tap into that air return cavity directly with the hallway having a large vent right there at the same spot on the other side of the cavity.
5. I understand this might not be 100% perfect with the heat generation in the office, but I'd like a large improvement and I think this will do it. Adding additional air conditioning into this room is likely too costly of a solution.

My questions:

1. Is there an obvious answer here? Is it bad to just vent the hot air into the hallway next to that air return vent out there?
2. If I go above the door, should I punch one hole in my office as high as possible with the second hole in the hallway as low as possible to maximize hot air going out while minimizing noise transfer?
3. How large should the holes be? If I go above the doors, should just 1 work or should I put 2 in, one over each door?
4. Should I use a "register booster" or other powered device to help push air through the return vent that I'm adding?
5. If I cut a hole into the existing cavity, how do I keep all of that drywall dust from going into my furnace (filter)? Or do I just do that and swap the filter out when I'm all done?
6. Is there something else I should be asking? I can definitely cut some holes into drywall but this is all new to me.

Answer 1

You could add a transom window above the door to let out the hot air passively since it rises.

It would probably look nicer too than sawing off the bottom of your door. Especially if you happen to have hollow core doors.

Answer 2

We’ve had several similar problems. We’ve solved them by 1) undercut the door, 2) through wall grille,3) through wall grille with sound baffles,

You’re right, you can’t “push” more air into the room without providing an air relief. (It’s the old straw example...you can’t blow into it if you have your finger over the other end. )

1) The simplest and quickest is to cut about 3/4” off the bottom of the door. We’ve done this several times and it works well, except you’ll loose a lot of your sound control. (The 3/4” will about the area of your grille.)

2) providing a through-the-wall grille above the door is also simple and you will also loose some sound control. This option has never turned out good for us. The grille is up near your ears so passerby’s can hear everything better.

3) We added a grille above a company’s presidents office door with sound baffles and it worked great. We cut the grille in just above the door header on the office side, then extended a duct with sound baffles up the stud space to a grille on the hall side near the ceiling.

The studs were 16” on center and we used the whole stud space. The duct was about 20” long and had 4 baffles. The baffles are made of strips of duct board mounted perpendicular in the stud space and about 4” apart alternating from side to side. This makes the air travel back and forth through the space. (We often use this design on large supply ducts to trap the sound of the motor noise coming on and going off on the supply side of heating/ac systems.)

It sounds like you have enough air when the doors are open...it’s just a problem when the doors are closed. (The straw example.) So, providing a “relief” vent seems like it will solve your problem. You’ll be “pushing” air out so it should not affect the house return air grille located close by.

Answer 3

Additional options you might consider:

1) Installing a small louver in one or both doors. If that doesn't work for some reason, you only have to replace the door(s).

2) Cut a small register in the existing return duct, then run a new small duct in the return air cavity to the wall. Perhaps a 4x6 or 3x12.

3) If the air return cavity is roomy enough(?) Cut a small return vent in the existing return duct, relocate some of the heat producing equipment into the space, and put a louvered access panel or a short door to provide easier access to the equipment. Obviously a printer would not work well in there, but a router, NAS, UPS could work quite well--IF there is enough space.