metal ductwork vs fiberglass ductwork


Hello,
I am going to be getting a new furance soon. The companies I have had give me estimates are pretty close together. Two of the three companies told me I should have my 35 year old metal ductwork replaced with fiberglass panel ductwork. I am told this will keep the air hotter in the ductwork and save engery. Apparently 10-15% of the heat in the air will be lost if I keep my existing metal ductwork. The cost for replacement is not really large, but is it a good idea?
Thanks,
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If the metal ductwork is insulated you loose some initial heat in heating the metal duct , like you would loose heating the fiberglass. After that it wont matter. If the duct is NOT insulated you have a radiator heating your attic space , or wherever the duct runs .
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No. Or Maybe. If your metal ducts are exposed to the outside there can be some heat losses to that environment. However, if the ducting runs in a basement it effectively supplies heat there so the loss is actually recovered. Even ducts in walls will radiate their 'lost' heat back into the room. Conductivity through fiberglass is less than metal, but not that significant. If you have had problems heating some rooms, then fiberglass to those areas may improve things, but I wouldn't expect any dramatic savings, just improved heat distribution. Buy a Trane system from a competent installer and you will be well served for a long time. HTH
Joe
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wrote:

Is the ductwork running through unheated spaces? If not, it doesn't matter how much heat you loose through them. If so, burrying them in insulation should work as well as replacing them.
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If you live in an area where frozen pipes are likely, it may be a bad idea to insulate ducts in a vented crawlspace. It seems to me that a cooler crawlspace increases the likelyhood of frozen pipes.
I'm not a plumber or an HVAC guy though, so I might be completely wrong.
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wrote:

imho:
I have fiber board ducts, and I can say, if you have metal stick with it. But upgrade it by insulating them. The fiberboard seems like a dust magnet, yeah I know if it's stuck in the board its not in my lungs. The idea about insulating your ducts in unconditioned space makes sense, maybe they can install boarding around your existing ducts.
Just a guess....
tom @ www.MedJobSite.com
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