Get It Inside!
No matter what part of the country you are in, placing the air handler/furnace and ductwork outside the thermal boundary of the home is not a good practice. Unfortunately it happens every day even in new construction.
Air Handlers or furnaces are not insulated well, and they leak like screen doors. When they are outside the thermal boundary of the home it is just like being outside. Ductwork, even when it is well sealed it is typically insulated with an R-4 or at the most R-8 insulation. I laugh when we insulate an attic flat with R-60 and then have R-8 ductwork that is connected to the living space ran in the truss webbing above the insulation. What is the effective R value of the attic?
It happens all the time. Why? I am not sure. The same thing happens all the time in the North with vented crawl spaces and basements that are not properly insulated.
This equipment and ductwork needs to be brought inside the thermal boundary. Sometimes that means that we need to change where the thermal boundary is or sometimes we have to build rooms or “doghouses” around the equipment. Sometimes we need to insulate over duct work. Whatever it takes to bring that equipment and ductwork “inside” is worth it.
There are many accepted methods of making the attic slopes and gables the thermal boundary in lieu of the attic flat. When you do this you can create a great utility space. This always costs more, but so does having the HVAC equipment and ductwork outside the thermal boundary. Sometimes that means we need to be using sealed combustion HVAC equipment. This has many benefits and doesn’t cost that much more. You should be able to use smaller equipment after making the home tighter with these changes. Sometimes smaller equipment solves under sized ductwork problems. This is a great side benefit. Smaller equipment means better comfort and smaller utility bills.
A good way to insulate the slopes if you have a good soffit and ridge vent system in place is to use foil faced ventilation chutes in between the rafters or trusses. After stapling these ventilation chutes in place and leaving a 2 inch ventilation space you can spray foam right to the bottom of them. The foil face will provide some radiant value to reflect the heat back out. We do these all the time. We call it redefining the thermal boundary from the attic flat to the attic slopes.
Whenever you take measures to tighten up a house you need to know what you are doing and follow proper building science procedures. You need to be concerned that combustion appliances still vent properly, you need to control moisture properly within the home and you need to make certain that the home has the proper ventilation when you are done with your work. All of these things should not be taken lightly but “The Juice is worth the squeeze.” We have never had such happy comfortable homeowners with minimal utility bills in all of our 28 years of business. The best part is that it is best for the environment as well.
There are millions of leaky inefficient uncomfortable homes out there. So, don’t worry, we won’t run out of things to do anytime soon.
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