Want to add a Return in the Mechanical Room

[bad_idea]

Nothing to do with the garage, sorry. I have central heat and air using a heat pump. 2000 sq ft ranch. I have a 8'x8' mechanical room with water heater, heat pump, and server rack. The server rack is a newer addition - nothing crazy - UDM SE, 24 port switch and a couple home automation hubs. As some might expect, the temperature in the mechanical room is getting a bit high. The return for the ac goes up into the attic, routed to an intake in the hall and another in the master bedroom (opposite ends of the house). The filter is mounted on the top of the unit.

I would like to cut an intake grille into the return near the ceiling in the mechanical room. I assume that would pull the hot air out of the mechanical room and pull in cooler air into the room through a louvered door. I'm not an HVAC guy, obviously, but I have installed ductwork before. I have no idea how large of a vent to cut into the return. Looking for some advice from some HVAC folks.

 

[jblnut]

Does the mechanical room open into the garage ?

 

[bad_idea]

LOL. No. The garage is a separate building. There is an ethernet drop that runs out to the garage tied into the server rack.

 

[FullRaceMerc]

We did that on a jobsite recently. Rather than tie into a return duct we ran a homerun to the return plenum. In this case it was a 4" duct to take heat off the ceiling of a tech equipment room. It's important to filter air from any return.

 

[danski0224]

If the room is closed and if the water heater is natural draft, it isn't a good idea without transfer openings.

 

[jlv03]

What kind of water heater do you have? If it is electric, have you considered replacing with a heat pump water heater?

 

[bad_idea]

It is a fairly new electric water heater. No gas appliances in the house at all. The filter is on top of the unit, between the return plenum and the air handler.

 

[pcmeiners]

What kind of water heater do you have? If it is electric, have you considered replacing with a heat pump water heater?

If you had an HP water heater, it has the ability to act like a large air conditioning unit plus if it is truly that warm it will cost extremely little for hot water cost, almost free but unless the room is very large the room will get very cold, and the efficiency will drop considerably.
Unless the devices in the room are producing a great deal of heat, the room is too small for a HP water heater. My HPW is in my unheated unused basement which is 26'x50', the entire basement is about an average 50° at all times.

 

[Fav Onefour]

It sounds like a return is already through your mechanical room but does not have an opening. Is that correct?

Based on your summary of equipment, it's entirely possible. Ironically, the server is the one item that would benefit unless you are using the heat pump for cooling as well. Is the heat pump being used for the cooling side and if so, how is it tied to the attic AC? Line set?

I know it's a lot of questions without any real answers. I'm asking because there may be other options. Heck, you could do the HP water heater and isolate that to cool the server.
In this case, the simple solution would be to add the mechanical room into your conditioned space with a simple opening in the return. Unfortunately, I can't tell you the opening size to keep your system balanced.

 

[bad_idea]

The heat pump in the mechanical room is a heat pump / air conditioner air handler. It is the central heating / air conditioner for the house. There is no AC in the attic, the return for the heating/cooling system is routed through the attic. I am looking for advice on what size opening to cut into the return plenum within the mechanical room.

 

[PoorUB]

With an 8x8 room you shouldn't need much, I would go with a 4x12 grill with a damper so you can close it down if you want. It wouldn't hurt to add a 2x12 supply if you have room in the supply duct. If the door to the room has an inch or so under the door it might pull enough air for the room through with out the supply.

 

[bad_idea]

Thanks! The door has a gap under it of ~1". If that proves to be insufficient, then I'll replace the door with a louvered one.

 

[Fav Onefour]

With an 8x8 room you shouldn't need much, I would go with a 4x12 grill with a damper so you can close it down if you want. It wouldn't hurt to add a 2x12 supply if you have room in the supply duct. If the door to the room has an inch or so under the door it might pull enough air for the room through with out the supply.

I like that approach.
I put a damper grill in my mechanical room. The room is smaller than this situation but my damper is barely open most of the year.
Return openings close to the main really draw.