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Question DetailsAsked on 5/4/2011

Space around ducts

I just bought a new central AC/Heat package unit. It replaced an old similar unit that was built in the 1970’s. The installer connected the new unit to the old ducts to save me money. The ducts are hard metal and appear to be in very good condition and an appropriate size and number, but a few places have torn or missing insulation and one or two are lying on the ground rather than being suspended four inches off the ground. The code in Memphis is that ducts must be at least four inches off the ground. However, I understand that this may not have been a requirement when the ducts were installed in the 1970’s. The ducts are in a crawl space which is bare dirt, not covered with plastic. The ones that are on the ground are in very tight places that will make it difficult, if not impossible, to dig the ground out from under them in order to create the required four inches of space unless the other ducts that are obstructing access are completely removed first. Part of the deal is that the installer will re-wrap the ducts wherever there is bare metal showing. However, I will have to pay extra for doing whatever is going to be necessary to get the ducts off the ground, and this may turn out to be very expensive. These are my questions: 1. Why is there a code that ducts need to be four inches off the ground? Is this really important? 2. Do the four inches include the insulation? In other words, are we referring to four inches from the ground to the insulation, considering that the insulation adds another approximately two inches, or are we referring to four inches from the ground to the bottom of the duct itself? 3. Once or twice in the 10 years since I bought the house, I could tell by gurgling sounds that water had gotten into one or more ducts after a hard rain. The repairman I consulted by phone instructed me to run the system on fan-only in order to dry out the ducts. He said nothing more was necessary. I did that and it worked. I haven’t thought any more about it until now. But now I’m wondering if this remedy was wise. Is there any problem when water gets into ducts that is not corrected simply by running the system on fan to dry out the ducts?

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1 Answer


Lana, this is a very serious problem and should be addressed a.s.a.p. First, these codes are written for a reason, to protect you, your home and all the occupants. The U.M. Code Book 604.2 states the duct-work needs to be 4 off the ground. That does not include the insulation. There is no mention of the distance between it (insulation) and the ground. This duct ground spacing is mainly for protection against water damage. Prolonged exposure or repeated exposures to water will eventually rot your duct system. I disagree with the contractor who made the statement "Turning the fan on.... nothing else is required." Absolutely correcting this water issue is required. You not only need to worry about the possibly of rusting duct-work but also mold and mildew contaminating the airstream into the house through this exposed duct system. Code also requires an 18 clearance for all duct-work that might obstruct access to other portions of the crawlspace. If you don't address it now you will most certainly do so when you sale the house or when some other catastrophic event causes you to do so!


Answered 9 years ago by Stans HVAC

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