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Old 10-18-2019, 06:25 PM   #1
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Need help with adding air return for one room


Hey guys,

I installed a home-network server rack in my laundry room. It contains a bunch of hardware that generates plenty of heat. The rack is ventilated with a fan on-top of the rack and pumps the hot air into the room.

The room has an incoming air supply (connected to a 6" flexible duct in the attic). Cold air is coming in, but the hot air has no place to go. The room is at around 86 F while the thermostat and the rest of the house is at 75 F.

Obviously I need a air return vent.

For the entire house there is only one existing air return box. It is located in the living room. All bed rooms have jumper air returns into the living room area.

Now, for the hot air in my laundry room I do not want another passive jumper air return, but have this ventilated directly from the server rack into the HVAC return. The existing air return is a 16" flexible duct.

I did some research and it looks like that in almost all case they make use of a dedicated air return box in the attic. Now, since I'm only going to add one return for one room, I'd much rather splice a Wye duct into the 16" flexible return duct. Wye ducts are - as far as I know - only used to supply cold air, but not for returns.

Below is a photo of the wye duct. In my opinion a wye shaped duct has less air resistance than a square return box, hence is favorable for my case.

I added a few photos of my situation.

What do you guys think? Air return box, or wye duct, or something else (I won't install another AC for this)?
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Need help with adding air return for one room-img_2802.jpg   Need help with adding air return for one room-duct.png   Need help with adding air return for one room-img_2801.jpg  

Last edited by McCarthy; 10-18-2019 at 06:28 PM.
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Old 10-18-2019, 06:59 PM   #2
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Re: Need help with adding air return for one room


Rather than returning this hot air to your system, is there a way to vent it outside. You could have non return baffles to keep cold/hot air from returning. Just thinking.
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Old 10-18-2019, 07:18 PM   #3
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Re: Need help with adding air return for one room


Problem with exhausting the hot air is you will create a negative pressure in the rest of the house and you will pull unconditioned air in from wherever it can get in. Cut a wye or tee into your 16" return. Does your server room have a door? If so you may need a transfer grill or undercut the door. You will need to run the fan all the time. Best thing for your situation would be a ductless split.

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Old 10-18-2019, 07:22 PM   #4
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Re: Need help with adding air return for one room


Quote:
Originally Posted by chandler48 View Post
Rather than returning this hot air to your system, is there a way to vent it outside. You could have non return baffles to keep cold/hot air from returning. Just thinking.

As spitz1234 said, this will create a negative pressure, and not only suck unconditioned air in, but also contaminated air from the attic. The last thing we want is the dust from the blow in insulation in our living spaces.

I want to stay within the HVAC envelope.
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Old 10-18-2019, 07:36 PM   #5
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Re: Need help with adding air return for one room


Quote:
Originally Posted by spitz1234 View Post
Problem with exhausting the hot air is you will create a negative pressure in the rest of the house and you will pull unconditioned air in from wherever it can get in. Cut a wye or tee into your 16" return. Does your server room have a door? If so you may need a transfer grill or undercut the door. You will need to run the fan all the time. Best thing for your situation would be a ductless split.

Sent from my SM-G960U using Tapatalk

Thank you for confirming my idea. The room does have a door, and there is about a gap of half an inch at the floor. Problem is that the heat stays further up and not much gets pumped out.

I will create an airtight seal all the way from the 6" collar in the ceiling and down to the server rack housing. The fan on the rack will stay in place and be running 24/7. The fan can be regulated as well.

If my AC unit runs out of steam in the next summer I will consider a ductless split. Meanwhile I will remove some kinks in the existing flexible ducts and make room for a bit more efficiency.

Any ideas what to use for the transition through the ceiling? I will need a collar on both sides for a proper seal against the attic?
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Old 10-18-2019, 08:20 PM   #6
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Re: Need help with adding air return for one room


Use a hard pipe thru the ceiling for better fit and easier to seal.

https://www.amazon.ca/Ideal-Air-7364...91060510&psc=1
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Old 11-09-2019, 06:24 PM   #7
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Re: Need help with adding air return for one room


Just put a filtered 12"X12" return air duct in the ceiling with a 6"-8" plenum and run a duct to any return duct or to the return side of plenum on your furnace. It will make your heating/cooling system work better and it will not make any difference if the door is open or not.
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Old 11-12-2019, 10:13 PM   #8
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Re: Need help with adding air return for one room


You may want to run a 8" Return to that room, it will put the room at a very small negative pressure to help get that hot air out. The door being undercut will help bring air from other parts of the house into that room.

I would install a 12"x12" RA grill with a 12"x12"x8" box on the top of it, connect the flex to the 8" round on the box and then put a 16"x8" Tee in the return main.
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Old 11-14-2019, 06:47 PM   #9
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Re: Need help with adding air return for one room


So you will use the power of the fan on top of the servers to push the air up a new duct into the main return duct? Otherwise you are counting on the (periodic) suction from the HVAC unit to pull the air out, which might not be running for long periods.
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Old 11-14-2019, 08:56 PM   #10
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Re: Need help with adding air return for one room


[QUOTE=puttster;5980585]So you will use the power of the fan on top of the servers to push the air up a new duct into the main return duct? Otherwise you are counting on the (periodic) suction from the HVAC unit to pull the air out, which might not be running for long periods.[/QUOT

With some T-stats, he can set his furnace fan to run at other times while the furnace is off. Not an ideal situation but he said he wants to hook it to the RA....
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Old 11-15-2019, 06:46 AM   #11
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Re: Need help with adding air return for one room


A couple points to ponder:
- When the HVAC idles, the server fan will then be pushing (although small cfm) into the return duct. Depending on how far the main return grill is, you may also hear that.
- Laundry rooms do have a lot of lint dust floating. Make sure you seal the dryer exhaust and empty the lint trap outside this room.
- Piggybacking on the house cooling is one method. What about when you're heating in winter? You can close the vent off but you'll still be generating lots of heat (not to mention when the dryer is running as well).
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