Need pro advice for a tricky one!!

Discussion in 'HVAC' started by Billbill84, Jul 16, 2019.

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  1. Jul 16, 2019 #1

    Billbill84

    Billbill84

    Billbill84

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    Hey guys. I posted a few weeks ago about an issue I had where the supply trunk off the air handler was sweating in my finished basement. Not a drop ceiling, all drywall so I can't see what's going on exactly, can only see what's pictured below before trunk runs above drywall. All vents are open throughout house and basement. Hasn't sweat in a couple weeks after I left doors open to my "mechanical" room and opened basement supplies now today sweating on supply trunk is back! Granted it's 84 out with 70% humidity outside.
    Here's the facts: 1) my new LG 70 pt humidifier runs constantly and pulls about 1.5 gallons out in about a full 24-28 hr before its full. My basement humidity is never above 50% in any spot.
    2) I peeked above ceiling drywall for further sweating but it looks like the supply trunk is only sweating where it's exposed in that room (about a 8Ft run pictured and ONLY spot that the cold supply runs about 1/4" parallel with the return-it splits off right where it disappears above drywall)
    3) The BIG question---(just dawned on me today, Could it be the return trunk causing the sweating on the supply trunk due to its extreme close proximity to each other?(1/4")
    I'm thinking the temperature difference between the two because this is the only spot of duct trunk sweating. Tested humidity in that room and it's 39%! Another thing is that it's only sweating on that side-next to the return trunk! The side that's butted against the drywall wall is bone dry!
    Please offer any thoughts. Thanks!
     

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    Last edited: Jul 16, 2019
  2. Jul 17, 2019 #2

    kok328

    kok328

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    Insulate the supply duct and see what happens.
     
  3. Jul 17, 2019 #3

    slownsteady

    slownsteady

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    Don't know if there is any wiggle room in the vents, but a thin sheet of foam board might slip in there and do the trick. If you can't find thin-enough foam board, you could even try FunFoam which can be found at the local crafts store.
     
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  4. Jul 17, 2019 #4

    Billbill84

    Billbill84

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    That's what I was thinking just slipping something between there to stop this.
     
  5. Jul 17, 2019 #5

    hornetd

    hornetd

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    We have to be very careful with using any kind of "foam" inside air ducting. The "Smoke Contributed" rating of many of those products is beyond the top values of the standard product fire tests. In the event of even a small fire impinging on the exterior of the duct the foam could ignite inside the duct and once ignited and fanned by the air handler blower it would give off truly poisonous fumes and dense smoke that would reduce visibility to inches. If it doesn't kill you in your sleep it will make it very difficult to escape the home. Even foam products which are rated self extinguishing may burn in the draft from the air handler blower.

    --
    Tom Horne
     
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  6. Jul 17, 2019 #6

    bud16415

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    I don’t think you are getting condensation between a warmer and cooler duct. You need air and air with moisture in it. hot on cold steel wont do nothing except warm up your cold air inside the out duct. The problem IMO is the ductwork is open in that area where the rest is insulated by the ceiling to some degree.
     
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  7. Jul 17, 2019 #7

    Billbill84

    Billbill84

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    Great insight thanks Tom
     
  8. Jul 17, 2019 #8

    Billbill84

    Billbill84

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    Hmm yeah, I see what u mean. I got a chair in different spots in that room and peaked above the drywall in spots and don't see any condensation on any ducts above drywall...that I can see.
     
  9. Jul 17, 2019 #9

    hornetd

    hornetd

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    When it comes to Heating, Ventilating, and Air Conditioning (HVAC) work I'm a pretty good electrician. So if you need HVAC work done then I'm a pretty good electrician. Keeping that in mind let me share a story that will show that I'm an habitual meddler. I was at a home doing electrical work; because I am a pretty good electrician; and the customer was having a parade of HVAC Company estimators in for prices on curing the sweating on the duct work.

    Since I fought wildfires for a living when I was a lot younger I had studied up on the effects of humidity in the air and how it interacts with the stuff on the ground. The basic objective is to be able to estimate how fast the fine fuel moisture will change in the weather that you have now and during the next burn period; which is the part of the day were the fire will burn the hottest and spread the fastest.

    Water cannot condense on the ducting unless you have enough of it in the air. If you had the instrument needed to measure relative humidity; which is a psychrometer; I suspect you would find that it is pretty high. Some air handler blowers have speed adjustments for the blower motor. Between estimator visits I changed the blower motor drive belt to the next larger pulley on the blower shaft and reset the alignment and tension on the motor pulley. The fan ran visibly slower. By the time the next "expert" carrying his clipboard and calculator arrived 3 hours later the ducts were no longer "sweating."

    That speed adjustment can be either electrical or mechanical. You will have to check the installation manual for your air handler to see if yours has either and how to adjust it. If the evaporator coils are clean and the condensate drain is clear and working well the blower motor speed may be the next thing to check. If it has a speed adjustment then slow it down to the next slower speed. That will cause the air to move slower through the evaporator coils which means that more moisture will condensate on the A frame and drain away through the condensate drain. That will leave less moisture in the air inside your home and that will lower the dew point. The dew point is the temperature at which airborne moisture will condense into liquid water. That temperature is not the same as the temperature at which it will condense onto colder surfaces but they are directly related to each other. If you get the relative humidity in the home air down to between 40% and 50% that is a good range for comfortable air. It is also likely to be too low a relative humidity and dew point to support the condensation on the surface of your duct work. A great side effect is that dryer air feels cooler. That will mean that your home will be more comfortable without having to run the AC any more than you are now. It might even result in your family being able to be comfortable at a somewhat higher temperature. That could save on your air conditioning costs.

    FWIW YM Will V

    --
    Tom Horne
     
  10. Jul 18, 2019 #10

    Billbill84

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    Wow very informative thanks Tom. It's just so weird because it's the only trunk with the sweating only on that corner edge. The other supply that runs in the opposite direction doesn't have any sweating whatsoever. If I had high RH wouldn't the other trunk sweat too then? It's just that one trunk on one corner edge. Even that same trunk isn't sweating on the other edge which is why I began to believe that the hot air running through the return could be creating some kind of barrier between it and the corner edge of that supply.
     
  11. Jul 18, 2019 #11

    hornetd

    hornetd

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    I did warn you that "When it comes to Heating, Ventilating, and Air Conditioning (HVAC) work I'm a pretty good electrician." That was meant as a warning that I'm no expert and I could be dead wrong. That said it did work for me once before. It is true that if the relative humidity in your house were lower you and your family might find it more comfortable without spending more money. I cannot guarantee that it will cure the condensation challenge but it might. You're the one who is there to actually see it.

    Is your HVAC System based on a heat pump? Heat pumps have a much higher tendency to chill the air too fast to dehumidify properly. That is because they have to be sized for the heating load which makes them larger than they need to be for the cooling. Heat pumps are more likely to have an adjustable speed blower to compensate for that. As I said before it is worth checking out for the other possible benefits even if it does not lower the inside humidity enough to prevent the sweating.

    --
    Tom Horne
     
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  12. Jul 18, 2019 #12

    Billbill84

    Billbill84

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    Great insight thanks Tom. I honestly have no idea if my system has a heat pump. Gonna check
     
  13. Jul 19, 2019 #13

    WyrTwister

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    Absolutely .

    In addition to the insulation , check , repair , replace , install vapor barrier .

    And if / when you see the sweating , cut the humidifier off .

    Wyr
    God bless
     
  14. Jul 19, 2019 #14

    hornetd

    hornetd

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    If the system humidifier runs at all during high humidity conditions then it's setting is way off. The highest relative humidity that the control should be set to turn the unit on is 50% maximum. The healthy humidity range for most persons is 40% to 60%. The only time you would need a higher relative humidity would be in a room were there are people with certain kinds of medical conditions and a higher humidity has been prescribed by a medical practitioner.

    --
    Tom Horne
     
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  15. Jul 20, 2019 #15

    Billbill84

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    Hi Tom. So today was extremely humid and hot out here near Chicago (northwest Indiana specifically), and I came home from work and checked my air handler in the basement and that sweating supply duct was now sweating on BOTH edges unlike before. The other supply trunk that runs off the top of the air handler in the opposite direction (think a "T" shape), is still bone dry as it has been. It's as if this sweating is mainly on everything on the other side of the handler. So I moved my dehumidifier, which was reading 50-55% humidity, in the room near the air handler and I'll see if I notice any improvement. It's weird because it's obvious there's a moisture source in the mechanical room but the dehumidifier only 55% never seen it above that. I don't have a psychrometer to test RH so with 55%, could the RH be way higher and the dehumidifier is kinda deceiving me? Thx
     
  16. Jul 24, 2019 #16

    hornetd

    hornetd

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    Depending on the size of the dehumidifier it may be too small for the amount of air that it is trying to "dry out." Get out the manual and see what size of space it is rated for and follow up on the fan speed issue.

    --
    Tom Horne
     
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  17. Jul 25, 2019 #17

    slownsteady

    slownsteady

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    I did not intend to make anyone think I would put the insulation inside the vent.
     
  18. Jul 25, 2019 #18

    hornetd

    hornetd

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    Since that was not clear to me at first I was concerned others might read it the way I read it. No offense intended. In 45 Years of active fire and rescue service I have seen things that I would not have believed anyone would do. I encountered a family that had made a play cave out of foam products; all of which were prominently labeled "Do Not Leave Exposed" or Must be covered with i/2 inch of plaster or equivalent. Many of you are too young to remember the Station Nightclub Fire that occurred on Thursday, February 20, 2003, in West Warwick, Rhode Island. 100 people were killed and 230 more were injured badly enough to require immediate medical care. The underlying cause of that disaster was the use of exposed insulating foam products to deal with the noise complaints being made against the club. The source of ignition was the pyrotechnic display that was put on by a band that was playing that club. Fire in some exposed foam products will spread faster than a healthy fit adult can run. Under the influence of a constant air flow, such as inside Heating, Ventilating, and Air Conditioning (HVAC) ducting; it will spread at a rate that is beyond the range of speed of spread rating that is used in the standard industry test of flame spread for interior finishes. More significant in the numbers of deaths and injuries was the smoke contributed when any quantity of many foam insulating products is burning. I responded to a mass casualty incident as the first arriving Emergency Medical Technician and once was more than enough to make me never want to go through that again. I also am unwilling to let any opportunity go by that gives me a chance to educate people on the things that have caused these incidents in the past. That said I was not trying to bash or belittle anyone.

    --
    Tom Horne

    Well we aren't no thin blue heroes and yet we aren't no blackguards to. We're just working men and women most remarkable like you.
     
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  19. Jul 25, 2019 #19

    Billbill84

    Billbill84

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    Well your input is valuable to those like myself, so thanks for that:)
     
  20. Jul 26, 2019 #20

    slownsteady

    slownsteady

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    Yup, we're all good. Just wanted to clarify myself.
     

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