Replies

1. 
   user-477743 | Aug 07, 2015 09:42am | #1

   Heating System in Attic

   It is now widely accepted that placing your HVAC system in an unconditioned attic is a bad decision from an energy use point of view. In the Summer, all the cooled ducts will be heated by the hot attic. In the Winter, all the heated ducts will be cooled by the freezing attic.

   If you must place your HVAC system in the attic, then you should place insulation in the roof joists. This is a more expensive proposition because the angled section of the roof is longer in length than the flat attic deck where insulation is normally place. For example, if the top of the ceiling joists measure 20 feet in width, and the roof is a 6/12 angle (33 degrees), then the combined length of the roof joists would be 23.8 feet in length.

   Note: Placing the HVAC system in the attic also means you have to be extra careful about an overflow/leaking AC unit. You'll need a condesate line out to the outside plus a secondary condesate pan under the unit in case the first one gets clogged/blocked. An overflow alarm is also a good idea.

   Additionally, it is MUCH harder to place insulation overhead vs just rolling it out on the attic deck. Really, spray foam is the only option that works overhead in terms of air sealing, and that is a very expensive proposition. However, in terms of energy, you'll recoup the additional expense of foam over leaky fiberglass over the life of the house.

   It sounds like you are in the design phase of building your house. My recommendation would be either 1) bite the bullet and condition/insulate the attic and place the ducts there; 2) move the compressor away from the house (you can go up to 300' in some cases); 3) build the first floor ceiling 1 feet higher and place your ducts in that space, then insulate the attic deck conventionally.

   Regardless of what option you choose, you MUST get a Manual D calculation done so that you get the right sized AC/HVAC equipment ($300-$450). Involve an HVAC technician early in the process in regards to moving the compressor away from the house.

   Good luck.

1. 
   DanH | Aug 07, 2015 01:26pm | #2

   Furthermore, the unit needs to be supported by framing that is somehow isolated from the ceiling joists, to avoid conducting vibrations through to the ceiling.

1. 
   GregWarren | Aug 09, 2015 09:12am | #3

   Thanks for the replies. I will take them into consideration. Why do builders put the Heating and air system next to a living space wall. They make a lot of noise. Why not put it against an exterior garage wall? Also the heating ducts run throughout the attic space so I don't quite get what the first reply is addressing other than a cold heating and air system and the condensation issues. Our last production home had the system in the attic on a pedistal above the ceiling beams and we never heard it running.

1. 
   DanH | Aug 09, 2015 09:47am | #4

   Well, in our case the furnace is in the utility room in the lower level of our split entry, adjacent to our bedroom.  And none of the air ducts are in the attic.

2. 
   deadnuts | Aug 11, 2015 10:04pm | #5

   yes

   GregWarren wrote:

   Does cold/snow weather effect a heating system in the attic?

   Sure it does. To understand why, you just have to ask yourself, does it matter wearing a heavy coat while exposeing yourself to winter weather?