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Question DetailsAsked on 10/23/2016

If your duct work got flooded during hurricane should it be replaced

My duct work got flooded during hurricane Matthew. 2 weeks later I turned on a/c unit and could hear it goggling water, found water in the return which is in the floor. Should all the duct work be replaced and should I use the unit. I did poor a little Clorox in when the water was in the return. It has gone down now but is still wet.

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Assuming fresh water infiltration - to be sure what the situation is, after drying it out you would have to run an extended reach fiber optic camera in there after drying it out to see how much rust you accumulated - some air duct cleaning companies have them, sewer cleaning companies have them too. Also - if short run from vents, rentable at tool rental places. If nice straigtht runs, you might be able to just remove a couple of duct vents (if directly connected to this underfloor duct) and use a hand mirror and flashlight - put the mirro down in the duct at about 45 degree angle and shine a bright flashlight (like a 6V lantern) on it to look down the duct.

As I understand if, the water mostly drained away (sounds like this is under a slab or maybe in a crawlspace) so it is wet but not full of water like before.

I am assuming metal ducts here. I would dry it out and it would normally be OK - to dry it run furnace (assuming you have hot air furnace or hot air from a heat pump air handler unit) at a temperature higher than normal for the house, AND make sure the humidity gets outside - leaving windows open enough to ventilate the house but not enough to make the furnace run more than say about a third to half the time. Or you could alternate between heat for awhile, then fan-only for an hour or two till the house cools down, then heat it up again - but the warmer than duct termperature furnace air is what is really going to evaporate the water fastest. IF just wet - not pooled in the duct - something like maybe 3-4 hours should be enough, maybe a half day to day if there are some puddles.

Of course, this assumes the A/C outside unit, furnace, or air handler itself (fan unit and A/C evaporator and any electrical dampers/ controls or such) did not go under water. IF they did you need a Heating and A/C contractor to look at them BEFORE use - to dry out thoroughly, check for electrical problems, and usually replace any electrical components that went under water. Generally, if the whole unit went under, it is replacement time - by law in some states.

IF it was salt water that inundated the ducts, a tough call - personally I would have the under-floor part wet cleaned by a HVAC company (inside and outside if exposed in crawlspace or such) and then dried out and sealed (probably 2 trips total). There are rust-inhibitor sprays they can use instead of a normal duct sealer, though not all HVAC companies have tht capability. Will not do anything about rust-through from the outside of the duct, but I would not tear up a floor and replace ducting in anticipation of rust-through unless it was being paid for by insurance as part of a larger flooding claim. If you are at an elevation where salt water intruded from Matthew, it is likely your soil is salty and would have corroded through eventually anyway if the ducts are in contact with the ground - so I would just wait till it happens and address it then - can be 10-20+ years with good materials and ground conditions that are not generally damp. If above-ground, washing them with hot water or steamto remove the bulk of the salt (assuming that can be done without further flooding the house) then spraying with rust inhibitor should take care of the situation OK.

If plastic flex ducts - I would dry them out and call it good - the salt and/or silt from the water (if any) is not likely to cause any problem unless you are real allergenic (to the dust) - might be a touch dusty the first few times you use the HVAC system - you can reduce that by taping a layer of swifter sheet or a layer of quilt batting or flannel over the incoming air vents for a week or so to act as a dust filter. Do NOT use tight-woven material that will dramatically reduce the airflow - and if the fan on the HVAC unit sounds labored or higher-pitched after doing this you restricted the airflow too much. However, if real organic water or salt water, during humid conditions you might smell some organic or ocean odor from the ducts - if that is likely to bother you, then you might have to replace them (or take them out and wash them and replace if in good shape) because it is pretty near impossible to clean fine water-deposited silt or salt out of plastic ducts in-place.

One other thing when it does come time to repair/replace below-slab ducts - in some states they now allow HVAC ducts to be in-place lined with polyester lining, same as water and sewer lines can be rehabbed - sometimes called "Chicago Duct Lining" or "Chicago Pipe Lining" because that is where it was first used on a large scale. Basically they inflate a polyester or fiberglass bag in the ducts so it fits tight to the walls - this is impregnated or sprayed with polyester resin (basically fiberglass resin) or a similar material, forming an in-place replacement lining. There are also spray-in linings that create a new interior to the duct. Avoids tearing out flooring so in the long run is much simpler and generally cheaper after all duct and floor repair and rehab work is considered.

Answered 3 years ago by LCD

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