Gas and Oil Home Heating Furnaces - Flexible Duct
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12-28-00, 09:30 AM
Is it safe to use flexible duct from the furnace all the way thru the house thus replacing existing duct(metal)? The reason being that the metal duct radiates so much heat that it creates massive ice on my roof.The existing ducts are insulated but were never sealed at the seams so heated air from the furnace heats the crawl space in my attic to the same temps as the inside of the house. This is an old cape cod stylye home and accessibility is limited. It would be so much easier to us flexible ducts vs. repair the old. If this can be used, are there adapters for the different size connection from the trunk line? Thank you for your thoughts.
PDF
12-28-00, 11:48 AM
IT comes in rolls.Wrap it under the duct and any open seams,bring it to the top of the duct,over lap it 4 or 5 inches and duct tape it together.I am not a sheet metal expert but our shop always insulates the inside of the duct.2 reasons #1 better insulating factor and noise dampering.PDF
12-28-00, 04:06 PM
Thank you for your response, however, I would prefer to avoid the old ducts as they pass through difficult places to get to and they are currently wrapped with R-11 insulation and stapled to complete. It would be so much easier to replace all with the flex if it is safe to do so. I have branch lines that are done in flex, but the trunkline is done with metal duct. I should also mention that this is a ceiling installation with registers at this level and the house sits on a slab foundation. Without tearing out the walls for new duct work, I would prefer to improve on the old set-up. Your thoughts?
fjrachel
12-28-00, 04:31 PM
Go for it, replace with flex. It's safe, but you may loose some air flow. Flex duct has a much higher resistance to air flow, especially if used for main trunk line.
12-28-00, 05:26 PM
All right! Now my next question is whether there are reducers available to go from a 12" trunk line to a 8" outlet? Probably would have to be in a "T" shape?
fjrachel
12-28-00, 07:09 PM
It's not that simple...I see you have no idea about what you are proposing. Is 12" going to carry the required cfm? at the correct static pressure for your system? No you cannot just 'T' off of the 12" and expect the air to follow. Have you thought about replacing your metal duct with duct board? It would be much easier.