tapping into main HVAC to cool insulated garage space = inefficient?


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Old 01-21-06, 04:16 AM
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tapping into main HVAC to cool insulated garage space = inefficient?

My home has a detached garage. The garage and the main house are connected by covered walkway that ties into the roofline and attic. The garage has a finished room in it that I connected to the main house HVAC via an 8" line directly from the main plenum, thru the attic space above the walk way. For the return I ran a 14" duct from the celing of the garage room thru the same attic space and to the celing of the closest room in the main house where the walk way attic joins.

The house is 2400 SF single story located in Houston (hot/humid summers and mild winters). The HVAC is a 12 SEER 5 ton unit. The entire garage is finished and insulated as it once had a sales office in it and it's own separate HVAC.

I installed the ducts last winter. This past summer noticed a big jump in my electric bill. I am thinking that this was, at least partially due to the new room that I air conditioned.

My dad thinks I am getting poor return due to a lack of a positive pressure return. I have to admit that in general the house and the garage room are not really well sealed. In fact the garage has a cloths dryer and an old non-working window unit in it that are potential air leaks.

Was this whole AC endeavor a bad idea?
 
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Old 01-21-06, 04:53 AM
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raharold,

Yes, in my opinion it is a bad idea to connect a garage to your house hvac system.
Here it is not permitted.
It is a serious safety issue from a fire and exhaust fume standpoint.

I would remove the duct you have installed and heat/cool this area separately.
 
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Old 01-21-06, 03:43 PM
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Hi GregH,

Thanks for your response. I understand what you are saying and have no doubt that it would be dangerous to connect a normal garage but this is into a separate room that is physically divided by a wall from the "garage" where I park my cars. I think of it similar to a house that has a built-in garage like is common here in Houston. That said, I am thinking I'm going to disconnect it anyway due to inefficiency reasons.

Thanks,
Ross
 
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Old 01-21-06, 07:41 PM
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I agree with Greg on this.

Even tho it's not part of the house, the duct still links to the house.. If the system was turned off, and you got fumes in the garage, the wind blows the fumes into the duct, and into the home.

Here we can not do such thing as well.
 
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Old 01-21-06, 08:56 PM
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Ross,

Codes vary but it is usual for attached garages to not be connected to the ductwork of the home.
Other than fumes, there is a danger of flames being drawn into the return air if there were to be a fire. You would need to have a fire damper at the garage and house if this ductwork connection was allowed where you are.
 
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Old 01-22-06, 12:46 PM
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Thanks guys. I'm going to remove the duct. Maybe I'll get an AC window unit for the room.
 
 

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