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Attic Furnaces, Air Conditioners, and Ducts

With the recent flooding in our area, there is a new a trend of putting Furnaces, Air Conditioners, and Ducts in attics. From the standpoint of making these systems less vulnerable to flooding, this makes good sense. However, from the standpoint of heating or cooling your home, and the efficiency of these systems, this is a terrible idea. 

The first problem with this plan is by locating the furnace and AC in the attic you are essentially putting them in the most inappropriate place possible. Attics are supposed to be within 10ºF of the outside temperature year round. The furnaces and ducts only have R-5 or R-7 insulation on them. Why would you put R-19 in your walls and R-38 in your attic floor to maintain the house at 68ºF, and then put the furnace and ducts that hold air under pressure at 110ºF outside this envelope and only insulate them to R-7? 

Generally there is a belief in the marketplace that a hot water heating system performs better than a forced air system. Furnaces have higher efficiencies than boilers, and yet, boilers often cost less to use to heat a home. Why is that? Truth be told, the reason is the distribution systems. Ducts leak a lot. Pipes don’t. If the water pipes in a hot water system leaked as much as the ducts in a hot air or AC system do, then no one would be able to sell a hot water system. When your 95% efficient furnace puts hot air in ducts that leak 50% of the air out, you don’t get 95% efficiency from the system. Unfortunately this is common, not rare. When your 85% efficient boiler puts 100% of that heat to the house WHERE YOU WANT IT, you get 85% efficiency. Duct leakage can be tested using blower doors and duct blasters. The leakage rate can be proven. (For a listing of practitioners to do this testing, visit www.BPI.org  or www.getenergysmart.org) Leaks can be sealed, IF the technician can get to the site of the leaks. Unfortunately, when the house is normal size, an attic duct system usually obstructs access to a point where technicians cannot maneuver through the attic well enough to seal the leaks. 

This winter, people in our area who put furnaces in attics will see huge heating bills and big time ice dams on their homes. Some charlatans will say the problem is the roof is bad. It is not. Some will say there is no way to fix this problem, live with it. This will be impossible for some people who already are financially strapped because they are still recovering from the flood. Some will say insulate the roof deck. This can be done, but the insulation product that must be used is urethane foam. There are two problems with that idea. One is the cost of foam is so high most people will not do it, the second is to do foam right, there has to be access to the entire roof, including right along the edge where the roof meets the outside wall. Accessing the edge is always difficult. If ductwork is in the attic it can be impossible. Insulating the roof deck with fiberglass is usually impossible because the fiberglass cannot be properly installed. 

The best solution to this problem is to convert the house from forced air to hot water. If the house was flooded to the point where this change is being considered, then the basement is stripped of all finishes, ducts, and appliances. Find a closet on the main level to house a boiler and indirect water heater. Run the necessary piping in the basement ceiling and install new radiators. The cost of this change will be higher than the cost to install a furnace in an attic unless you tell the HVAC guy you want him to guarantee and prove there are no leaks in the HVAC system in the attic, and you properly insulate the attic to house the heating system before the furnace is installed.

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