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Condensation dripping from cold air return chase


Mark P
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There is a good amount of condensation dripping from the bottom of the cold air return in the crawl space directly below the furnace/a-coil. The outside temp was around 90 and the a/c had been running all day.

Is this a condition frequently found? What is the cause/fix?

Thanks

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Hi,

Are the ducts insulated? If not, they should be. Write it up. Is the condensate drain from the A-coil clear and draining properly? If not, write it up. Is there a cap sheet on the floor of the crawlspace to minimize the amount of moisture evaporating from the soil which can evaporate on the plenum? There should be. If not, write it up.

OT - OF!!!

M.

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Okay,

What's the humidity like in your area? If the exterior humidity is higher than that found in the crawl, and you've got open foundation vents, any humid air entering the crawlspace from the outside through the vents is going to condense on surfaces in the crawl.

OT - OF!!!

M.

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Hi Mark:

I highly doubt that the duct is insulated or else it wouldn't be sweating like that. They would insulate the supply duct(s) but not the cold air return. Without a crawl space the cold air return would be in the same environment as the conditioned air so no sweating however, when the cold air return hit's a hot&humid crawl space you'll get condensation. Just a matter of dew point.

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Yes, your right the return air duct (in the crawl space) is not insulated the supply duct is insulated flex. The condensation is only on the return air (sheet metal) directly below the inside unit, so I don't believe it is the outside humidity. I was thinking an undersized coil. At any rate I told them I did not know the cause of the condensation, it is time to have the 23 year old unit undergo routine servicing by a HVAC specialist and to bring the condensation question to his/her attention when that is done.

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Hi,

You've just answered the question. The ducting in the crawl is not insulated. If you've got an AC system with ducts passing through the crawl, all of the ducting in the crawl needs to be insulated if you want to avoid condensation. Otherwise, that cool duct is going to cause the ambient moisture in the air to cool to dew point and condense on it the same way it will condense on cold uninsulated plumbing.

ONE TEAM - ONE FIGHT!!!

Mike

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I don't want to sound like "Kurt", but there seems to be some real basic mis-understandings of a basic system and the operation of same. Maybe I am reading this thread wrong, but much of it seems to indicate further reading on basic HVAC is called for. Mike is right, and I don't think solutions like dehumidifiers are appropriate.

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At any rate I told them I did not know the cause of the condensation, it is time to have the 23 year old unit undergo routine servicing by a HVAC specialist and to bring the condensation question to his/her attention when that is done.

Routine servicing my foot! The blasted thing is 23 years old, its time to replace that energy hog even if it is still working!

I must agree with Les, a little refresher course on how the HVAC works might be in place.

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  • 5 years later...

My unit is a 3 year old carrier. The air handler in located in the crawl space which has a concrete floor. All foundation vent are open. The humidity here in NC is high. The problem started about six months ago. The problem is that the return air plenum which is sheet metal with insulation wrapped around it has been constantly dripping with condensation. One company recommended that I close all the foundation vents and another says I should buy a dehumidifier. May I have some comments on these two solutions, please.

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Ventilated crawlspaces often have issues with high humidity. If the air in the duct is cooler than the crawlspace air then it's more likely that the outer surface of the duct will be below the dew point of the crawlspace area.

There's a wide variety of solutions to consider, depending on the particulars of your crawlspace. None are easy or inexpensive. Some may not be appropriate for your situation. A visit from a skilled home inspector is probably the best advice I can offer. You don't want to start letting go of your repair dollars until you've got the right course of action figured out.

Marc

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