Room to room fan or cold air return tap in?


  #1  
Old 06-01-05, 06:49 AM
chamill
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Room to room fan or cold air return tap in?

In the summer our office (insulated, over the garage) with three computers gets very warm as the day progresses. I have adjusted the dampers in the ducting in the attic to blow more cool air in here and that has helped some, but I think that as the North Carolina summer approaches that the temp will rise again.

Our current setup:

2 registers in the ceiling of the office. These registers are fed directly from one line out of the blower box in the attic. There are no cold air returns in this room.

The upstairs cold air return is down a hallway from the office, but is directly at the top of the stairs and is surrounded by 3 bedrooms and a bathroom door closer to the return than the office. I think that this return isn't pulling enough hot air out of the office because it is pulling so much air from downstairs and the other rooms that the pressure isn't enough to pull from the office.

Here are what I think my options are:

Install a room to room fan above the door from the office to the hallway to help move the hot air. Broan seems to have a model that might work for me. I would like to only have this fan run when the blower turns on with the heat or A/C. Does anyone know if this is possible? The blower unit is directly above this location in the attic, so running wires won't be an issue.

- or -

The cold air return ducting from the air intake downstairs runs directly behind the wall between the office and the rest of the house. I've considered tapping into that through a hole towards the ceiling to the left of the office door. The trouble with that, though is that the duct is directly behind the wall and I wouldn't be able to have it run through a filter before tapping into the duct...I just don't see how I could possibly do the filter with the setup as it is. Basically I would have to put a return into the wall and somehow tap directly into the duct right there next to the return with no duct run to the cold air return. Is it ok to feed the furnace with unfiltered air? Any tips on how to tap into the cold air return when I don't think I can properly set up the return vent with ducting to the main cold air return since it is right inside the wall I want to tap in through?

Please give me some feedback and let me know what you think of these solutions or give me some other ideas if you have any. Thanks!
 
  #2  
Old 06-01-05, 05:33 PM
JohnT
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Ducts

How big is the office?

What are the duct sizes running to the two supply grills?

Do you keep the door of the office closed for the most part?

It is not a good idea to feed unfiltered air to the furnace unless the filter is at the furnace. Where are your filters?
 
  #3  
Old 06-02-05, 08:28 AM
chamill
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How big is the office? ~15' x 20'

What are the duct sizes running to the two supply grills? One 6" flex duct that splits in the ceiling to the two supply grills.

Do you keep the door of the office closed for the most part? It's open about 50% of the time, but doesn't seem to make a difference when it is open.

It is not a good idea to feed unfiltered air to the furnace unless the filter is at the furnace. Where are your filters? The filters are not in the furnace, they are in the wall downstairs and in the ceiling upstairs. I wanted to install a filtered return, but I can't figure out how to connect from the return directly into the return flex duct behind the wall since the duct is flat against where I would have to put the return.
 
  #4  
Old 06-02-05, 09:53 PM
JohnT
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Office HVAC

Well without a heat gain/loss calculation for the office it's not possible to determine what you need in the way of supply airflow needed to properly cool the room. Returns are important to assure proper airflow but it sounds like your supply ducts are a bigger problem. A 6" duct will supply about 100 cfm if the run is not too restrictive. I would hazard to guess you need at least three times that amount to properly condition the room. All the return in the world won't be able to overcome that problem.

A heat loss/gain calculation would be the right place to start, otherwise you could be just "spinning your wheels".
 
 

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