We have a retrofitted forced air propane heat and AC system in our house. All of the ducts are run in the attic and are the flexible aluminun looking ducts. It is my understanding that there is a great deal of heat loss from this type of setup. Does anyone have any advice on how to increase efficiency? Thanks
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I redid a house like that in which animals had torn through all of the flexible ducting. I used 1 1/2" duct board and made long chases down each side of the attic, and ran short drops of flex duct to ceiling vents. The foam board has an R-6 rating or something.
remodeler
There are a number of things to do to reduce the heat gain of attic mounted ductwork. Attic temps often reach 140 deg, and only R-4 or R-6 seperates the A/C air from the attic heat. It is easy to loose 30% of the cooling capacity to the attic heat gain.
1. Cool the attic, vent, radiant barrier, soffit vent etc. The goal is to get the attic to outdoor air temp, but without spending a lot of $ on energy to do so.The right radiant barrier/exhaust fan system can accomplish that goal.Ridge vents used with continuous soffit vents can also help.
2. Be sure the duct work is well sealed, check the boot end at the ceilings for gaps that are hidden by the grille face.
3. If the ductwork is suspended from the attic roof, thus hanging in mid air, see if you can drop it to the attic floor, and then bury it with a layer of insulation, like blown in cellulose. Build barrier walls using foam board to contain the insulation in you are trying to keep some floor area clear.
4. Minimize the length of each run, but keep some bend in the final few feet to reduce sound transmission. I was able to take out over 100 feet of ductwork in a house, reduced a lot of hot surface exposure.
That should get you started, and the pay off will be good if you are in a high cooling area.
Paul