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Discussion Starter · #1 ·
I noticed that my ducts in my crawl space are dripping moisture. What is the best way to seal existing duck work?
 

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What you need to do is insulate them to stop the condensation in Summer and heat loss in Winter. The best way to seal them is with mastic.
 

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Discussion Starter · #6 ·
What you need to do is insulate them to stop the condensation in Summer and heat loss in Winter. The best way to seal them is with mastic.
I was thinking that the cool air (AC'd) was leaking out the duct's seams and joints and causing the condensation.

The ducts are insulated although it is torn in places.
 

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Mine are under my raised house, they also sweat, and are insulated. Not sure if there is a way to stop it or not.
 

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If the condensate is forming inside the ducts and dripping out the problem is not just leaking ductwork. Sealing them without finding the source of the water will just form mini swamps in the ducts.

I would suspect your drain on the evaporator coil is plugged or some other problem, such as a bad condensate pump, is causing the problem.

Open the evaporator coil case and be sure it's draining and that the coils are clean. Dust and fuzz buildup and restrict airflow and cause high velocity spots over the coil which will wipe moisture into the airstream. This then collects in the ducts and causes these kinds of problems.

Left uncorrected you can build mold and all kinds of problems in the system.

Mike
 

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You may need to balance the air handler to increase the volume of air. The lower the volume, the colder the air and the greater the propensity for condensation. Some people close off too many registers, trying to limit how large a space they cool but the air then is colder because less of it is moving across the coil. Reduce the flow too much and the coil will ice up.
 

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Mine are under my raised house, they also sweat, and are insulated. Not sure if there is a way to stop it or not.
Not a real common problem in our area but I have seen it happen. Once the insulation is wet it is really of little value. It will dry and become nearly as effective as before being wet but the original problem will reoccur given the right conditions.

The cure is to add enough insulation to prevent the warm, moist air from reaching the duct. Be sure the existing insulation is removed or compleatly dry. If the existing insulation has a plastic or other vapor barrier over it this must be removed prior to adding insulation. If it's left in place and more insulation is added there can be problems of condensate forming between the new and old barriers.

Least ways this is how we solved these problems here where we don't have really high humidity.

For local advice I'd contact a well known and reputable HVAC person in your area. Local knowledge is always a good thing.

Mike
 

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You may need to balance the air handler to increase the volume of air. The lower the volume, the colder the air and the greater the propensity for condensation. Some people close off too many registers, trying to limit how large a space they cool but the air then is colder because less of it is moving across the coil. Reduce the flow too much and the coil will ice up.
In a properly designed system closing ducts will not cause the coil to ice up nor will the air become appreciably colder. The system will sense the reduced need for cooling and shut the compressor off while allowing the evaporator fan to run. When the system again calls for cooling, it's controlled by compressor head pressure and/or suction pressures, the compressor will again cycle.

Closing a number of registers can cause the system to thump and bang as ducts work under the higher pressures but this is not a common problem with most systems. What is common is for the louvered vents in the rooms still being supplies to whistle and moan due to the increased air velocity.

What usually causes coil icing is a low refrigerant charge. When the charge gets just to the borderline failure point the refrigerant boils out too quickly in the evaporator coil and causes extremely cold spots and ice. This spreads over the entire face of the coil rather quickly.

Just what I've seen doing this kind of work for a few years.

Mike
 

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Just what I've seen doing this kind of work for a few years.
Sounds like newer technology. Maybe the systems I've had to deal with are older than you. Some of my systems don't even have the low ambient air option and have issues cooling when it's colder outside than inside.
 

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I would not so much worry about sealing them .. more so insulating them REAL well.

I'm surely no HVAC guy but have been around commercial construction for many years. And have seen duct work sweat in un conditioned spaces, only to be cured with Duct insulation
 

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Discussion Starter · #15 ·
I would not so much worry about sealing them .. more so insulating them REAL well.

I'm surely no HVAC guy but have been around commercial construction for many years. And have seen duct work sweat in un conditioned spaces, only to be cured with Duct insulation
It sounds like the best thing will be to wait till late winter when all the existing insulation is dry from the heating season and then fix/add insulation (seal any joints that are leaking badly).
 

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Sounds like newer technology. Maybe the systems I've had to deal with are older than you. Some of my systems don't even have the low ambient air option and have issues cooling when it's colder outside than inside.
Older than me would be ancient.:trink40: I cut my teeth on the old ammonia systems and open wheel compressors. Even worked on one that had a hit & miss engine for power. It had replaced the old steam engine that was the original power source.

Some of the cheaper systems will give a problem with temperatures that are down near freezing when trying to condition a working space. Standard air conditioning systems have this problem sometimes. The better systems and those used for coolers and freezers set up properly will have a hot gas bypass that solves these low temperature operating problems. First systems I ran into that had this, now common, type of low ambient control was probably in the mid 50's. Have no idea how long it had been in service but it was far from new.

The OP's problem really sounds like a plugged drain on the evaporator coil drain pan. These often get stopped up with crud and require routine maintenance.

When we would put in a home system it was our standard practice to teach the home owner how to do the simple things like belts, bearing oiling/greasing, coil cleaning and keeping these drains clean. We would supply them with the brushes and "worms" needed for the jobs as well as the necessary tools to do the lube work. Real often we would find this kit sitting where we had left it when they would call for a problem. At least we tried to save them some bucks and I suspect that's one of the reasons we had so many repeat customers.

Todays systems are pretty much computerized and there is a lot of service work that is quite expensive for the home owner. Boards are expensive and usually not field reparable. I really prefer the old systems. Simple, long lived and less expensive. The new systems get a higher SEER rating but the savings are eaten up by problems down the line IMO.

But I ramble again.

Mike
 

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It sounds like the best thing will be to wait till late winter when all the existing insulation is dry from the heating season and then fix/add insulation (seal any joints that are leaking badly).
Great plan! Insulating the ducts will take care of your moisture problem.I see lots of sweating ducts both from tore up insulation as well as systems never insulated when originally installed.
 

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I guess I will try to double or triple the insulation on the duct under the house when it dries this winter. I really don't have another option I guess, it is exposed to whatever the humidity is outside. I do have a problem with drips coming from the registers over the great room but may have it fixed, that will be another thread in a few days if it starts again lol
 
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