Column Building ScienceS Supply AHU Supply Supply Return AHU Supply Return Figure 3a Base Case. The best of the best. Ductwork and air handler inside the conditioned space with a vented attic on top with an airtight ceiling and code levels of attic insulation. It does not get better than this anywhere anytime. Figure 3b Ugly and Unfortunately Typical. This is a 30% or more energy hit on cooling and heating compared to the base case. AHU Supply AHU Supply Supply Return Supply Return Figure 3c Less Ugly. The moment you put the ductwork in the attic (while keeping the air handler inside), having this ductwork airtight (installed by John Tooley himself) with an airtight ceiling (installation watched over by me), and all penetration and boots and stuff sealed, you still have about a 10% energy hit on cooling and heating compared to the base case. This is much better than Figure 3b, but it sure ain't Figure 3a. Is there another option? Yes. Take the John Tooley option, make the ducts airtight, make the ceiling airtight and insulate the bejesus out of the ducts by covering them with lots of stuff (Figure 3e). You can cut that 10% hit to less than 5%, maybe to 3%.‡‡ Now you just can't "bury" the ducts or they will sweat. You have to insulate them with Figure 3d Ugly Beautiful. Conditioned attic. With my unvented roof, conditioned attic approach we got the ductwork completely in the conditioned space but we increased the surface area of heat gain and heat loss. This is a 10% energy hit on cooling and heating compared to the base case because of the increased surface area. And here is a "heads up": don't buy the argument that you don't need as much "R-value" when you "cathedralize" the attic. You should install "code levels" of insulation when you do conditioned attics-sloping or flat or cathedral or whatever. an impermeable layer of spray polyurethane foam and then you can bury them (Photo 2). You need to do this in all climates except in the desert. Of course, while you are in the attic with that SPF why not take the opportunity to seal all those holes that are up there? Nothing works better ‡‡ The folks at the Consortium for Advanced Residential Buildings (CARB) have done some good work on this under the Building America Program (http://tinyurl.com/lkpmukq or http://tinyurl.com/mloydg3.). 56 ASHRAE JouRnAl ashrae.org D ecem ber 2013