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Air Handler (AC only) in the attic

My 1978 Ranch house in Zone 5 (Southern NY) was constructed with the AC Air handler in the attic. He(Heating is gas fired hot water) . I am replacing windows and re-siding - adding 2" of foam to the exterior. There is no good way to move the Air Handler into conditioned space, and I do not want to create a completely unvented attic.

Can I create an insulated unvented "Room" around the Air Handler, and if so, what is the best strategy? And do I remove existing insulation in the ceiling below the Air Handler so "connect" the space to the conditioned interior?
Thanks for any thoughts!

Asked by Mark Rubinsky
Posted Thu, 02/27/2014 - 12:16

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3 Answers

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1.
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Mark,
It's possible to build your proposed room -- perhaps. You need to be sure that there is adequate access in the room for maintenance -- in other words, room for a technician to have access to as many sides of the air handler as possible, as well as an access door.

The advantage of creating an unvented, conditioned attic is that you also bring the attic ductwork inside the home's conditioned space.

It doesn't matter too much whether you leave the insulation on the attic floor or you remove it -- as long as your new room is insulated to the minimum requirements for roof insulation in your climate zone.

As with any energy retrofit project, always pay attention to airtightness and air barrier continuity.

Answered by Martin Holladay, GBA Advisor
Posted Thu, 02/27/2014 - 13:24

2.
Helpful? 1

I'm just finishing up one of these right now. Depending on the house size, it might not be a great idea. I'd evaluate the cost relative to cooling via mini-splits. If a single outdoor unit with 3-4 heads has sufficient distribution it's pretty likely that the mini-split will be a winner. If you decide to proceed, here are my observations:
1) Run a Manual J and D for the upgraded system. I'll usually fix the airflow of the system within Man J to be my best estimate of current system (usually ~400cfm/ton). Then run Man D using this airflow.
2) Most duct systems are hopeless. Yours will be no exception. So rip out all ducts except for the boots.
3) With the new ducts, install fittings to keep the ducts really low to the ceiling.
4) Build the enclosure with the ducts ripped out so that you can minimize the penetration sizes for the ducts.
5) We use a hybrid of cc SPF and Thermax for the room. By dropping the trunk ducts we're able to spray foam on the unconditioned duct-work, sealing it to the drywall.
6) Use R 8 for the branches and bury everything in cellulose.

Answered by Jesse Smith
Posted Thu, 02/27/2014 - 17:56

3.
Helpful? 0

Thanks Martin and Jesse - both very helpful answers. I figured the concept was OK, but Jesse - you bring up an excellent point about the actual value of the idea. I had thought about mini-splits, but never really did the proper research. After some more investigating and some number crunching I may be back with more questions. Thanks again.

Answered by Mark Rubinsky
Posted Fri, 02/28/2014 - 10:42

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