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Thread: Condensation on ceiling in one bedroom after equipment change

  1. #1
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    Condensation on ceiling in one bedroom after equipment change

    I will list everything that has been done to the house (all were done by licensed professionals, but 2 separate companies):

    This is all in Boca Raton, FL in a 1900 sqft single family home with the air handler in an interior closet and ductwork in the (low slope roof) attic.

    Approx. 4 years ago ceilings were pulled down and all ductwork was pulled out. New ductwork was installed, all rigid metal round ductwork, every joint mastic'd and everything wrapped on the outside (including metal supply boxes) with I *believe* R-8 insulation. The air handler was not changed at this point, but everything from the plenum and beyond was. I personally inspected between each step to ensure nothing was missed, every joint mastic'd and every seam taped and made them go back over whatever was missed. They did not like me.

    After that the whole attic was re-insulated and 1-2ft of blown in pink insulation (unsure if fiberglass or cellulose) buried all the ductwork which mostly ran exactly 3.5" over the drywall (because of joists.) The thickness varied with the height of the attic at a given point (max 2.5ft at ridge) but at the point in question later, it is at the higher end of the range (parallel, directly under ridge).

    Fast forward 3 years and the air handler and outdoor unit was replaced with the *identical* updated rheem model (same exact size in interior closet, almost identical model number except the year.) 3.5 ton, 1200cfm i believe, etc.

    A month later a water spot appeared on the ceiling going into one of the bedrooms right at the intersection of the wall and ceiling, about 1 ft before the supply register in this room (I recall this being a tight fit over the top plate and then there was a truss of some sort that ran the opposite way so they couldn't go any further into the room with the supply. I also recall making them re-do the insulation in this area because the supply branch was so close to the top plate and they did a poor job but I thought it was taken care of.)

    So, why would an air handler equipment change cause this? I remember the first time the new unit was turned on, I thought it was defective because the old unit, by my hand, "felt" like the air blowing out of the ducts was colder than the new unit. And it took forever to cool the house, but the old unit would only cool the house to 76 by the time it perished (it was 20 years old) even if it ran 24/7, and the new one will cool the house to 72, eventually, and cycle on and off - it clearly works better. Also, this duct seems to have been undersized from the plenum, the velocity of the air coming out of the 3 supplies on this side of the house is slower than the velocity coming out of the supplies on the other side of the house, though this did not seem to change with the equipment change, and this room seems to be consistently 1-2 degrees hotter than the other rooms of the house.

    What's the theory behind what could be the cause of this, other than "something is below the dewpoint of the air touching it"? What would change with an equipment change to the identical (but obviously newer) equipment? Should this be examined with a thermal camera "inside" the duct or should the ceiling be cut out (again) or?

  2. #2
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    I read thru some of your old posts.

    Were any static pressure readings taken before replacing like for like?

    Were any static pressure readings taken before replacing the duct work 3 years ago?

    Were any static pressure taken after all this work?


    The common denominator here is the metal is below the dew point. Causes

    Over sized equipment

    or

    Undersized ducts

    or

    Combination of both.

  3. #3
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    Outdoor dew points in FL are about 70^ lately. With a vented attic, expect attic dew points that high or higher. Anything colder than 70^F will drip. You have covered your ducts with breathing insulation that is without a vapor barrier on the warm damp side. Moisture with move through the insulation and condense on the damp side of the cold duct. The duct may be less than 55^F. Is there any question about the what may happen. You need to insulate the ducts with a vapor barrier on the warm damp side. The vapor barrier must be above the dew point of the air.
    The lower that you set the indoor temperature, the more insulation that is needed to keep the vapor barrier above the warm, damp air in the attic.

    Now what!

    Warm the indoor temperature as much as possible. Most live with 75^F setting. You need a 45^F cooling coil temperature to get adequate dehumidification from your a/c. The air leaving the coil will be 53-55^F with a 75^F, 50%RH return. You see the problem is that you end up with a 55^F duct temperature.

    If you are unable to place a vapor barrier over the insulation surrounding the cold duct. Other tricks are used. On contractor with several homes with the problem, closed the attic vents and dehumidifier the attic down to 55^F dew point. This stopped all condensation problems in the attic. Also, consider allowing some warm air to by pass the cooling coil that will warm the supply air temperature enough to reduce condensation point in the area of the home with condensation problems.

    As search for real comfort in your home with out condensation problems on ducts and in the exterior walls during the seasons of high outdoor dew point, you will want to be able to control the indoor %RH to <50%RH evening and during rainy weather. During hours of low/no sensible cooling loads and high outdoor dew point, you need supplemental dehumidification. This done by installing a small whole house dehumidifier that injects warm dry air into the cold air supply duct down stream from the cooling coil. Of course the warm air warms the duct when the a/c is not needed and dries the damp side of the duct. Also the fan on the dehumidifier is operated during the cooling hours which also warms the supply duct temperature several degrees, which decreases the condensation problem.
    Many builders in high dew point green grass climates doing this to all of their homes. I suggest investigating units like the ULtra-Aire which has been doing this with +25 years and are made in Madison WI.

    Looking forward to your and the contractors opinion.

    Regards Teddy Bear

    Current dew points These are common in all green grass climates.

    Name:  Current dew points 2021-05-10 .png
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    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

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  5. #4
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    Quote Originally Posted by boca View Post
    I will list everything that has been done to the house (all were done by licensed professionals, but 2 separate companies):

    This is all in Boca Raton, FL in a 1900 sqft single family home
    with the air handler in an interior closet and ductwork in the (low slope roof) attic.

    Approx. 4 years ago ceilings were pulled down and all ductwork was pulled out. New ductwork was installed, all rigid metal round ductwork, every joint mastic'd and everything wrapped on the outside (including metal supply boxes) with I *believe* R-8 insulation. The air handler was not changed at this point, but everything from the plenum and beyond was. I personally inspected between each step to ensure nothing was missed, every joint mastic'd and every seam taped and made them go back over whatever was missed. They did not like me.

    After that the whole attic was re-insulated and 1-2ft of blown in pink insulation
    (unsure if fiberglass or cellulose)
    buried all the ductwork which mostly ran exactly 3.5" over the drywall (because of joists.)

    The thickness varied with the height of the attic at a given point (max 2.5ft at ridge)
    but at the point in question later, it is at the higher end of the range (parallel, directly under ridge).

    Fast forward 3 years and the air handler and outdoor unit was replaced with the *identical* updated rheem model
    (same exact size in interior closet, almost identical model number except the year.)

    3.5 ton, 1200cfm i believe, etc.

    A month later a water spot appeared on the ceiling going into one of the bedrooms right at the intersection of the wall and ceiling,
    about 1 ft before the supply register in this room

    (I recall this being a tight fit over the top plate and then there was a truss of some sort that ran the opposite way so they couldn't go any further into the room with the supply. I also recall making them re-do the insulation in this area because the supply branch was so close to the top plate and they did a poor job but I thought it was taken care of.)

    So, why would an air handler equipment change cause this?

    I remember the first time the new unit was turned on,
    I thought it was defective because the old
    Specific Model numbers are required to verify ID it is a matched system.

    What do the air balancing and commissioning reprts indiciate?

    Dip Switch Settings _________

    Total Air Flow Rate Measured _ _ _ _ CFM

    Total External Static Pressure ( TESP) _0. _ _ " W.C.
    ___________ Supply Side ________ _ 0._ _
    ______________ Return Side _____ _ 0._ _ " W.C.

    Supply Air Temp. ___ 'F
    Return Air Temp. ___ 'F

    ... for starters

    https://www.energystar.gov/ia/partne....pdf?5ace-789f
    Designer Dan __ It's Not Rocket Science, But It is SCIENCE with Some Art. _ _ KEEP IT SIMPLE & SINCERE ___ __ www.mysimplifiedhvac.com ___ __ Define the Building Envelope & Perform a Detailed Load Calc: It's ALL About Windows & Make-up Air Requirements. Know Your Equipment Capabilities

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    Quote Originally Posted by pecmsg View Post
    I read thru some of your old posts.

    Were any static pressure readings taken before replacing like for like?

    Were any static pressure readings taken before replacing the duct work 3 years ago?

    Were any static pressure taken after all this work?


    The common denominator here is the metal is below the dew point. Causes

    Over sized equipment

    or

    Undersized ducts

    or

    Combination of both.
    They did not take pressure readings before or after changing the ducts or changing the equipment. The ducts are sized to the maximum that fits, the plenum is the exact size of the outside of the upflow air handler and taken all the way to the roof (we had the roof off they went in from the top!) and the duct take off is a 16" tee with one side reduced to 12" I believe as it supplies 3/10 branches, approx 20% of the house. The model numbers on the equipment are RBHP21J11SH2 and RA1636AJ1NA, it is the same size equipment that was in the house before hand because everyone wants to oversize as everyone here says, so I specifically prevented them from doing so, I required identical upgraded equipment (it was impressive it lasted 20+ years anyways.)

  7. #6
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    Quote Originally Posted by boca View Post
    They did not take pressure readings before or after changing the ducts or changing the equipment. The ducts are sized to the maximum that fits, the plenum is the exact size of the outside of the upflow air handler and taken all the way to the roof (we had the roof off they went in from the top!) and the duct take off is a 16" tee with one side reduced to 12" I believe as it supplies 3/10 branches, approx 20% of the house. The model numbers on the equipment are RBHP21J11SH2 and RA1636AJ1NA, it is the same size equipment that was in the house before hand because everyone wants to oversize as everyone here says, so I specifically prevented them from doing so, I required identical upgraded equipment (it was impressive it lasted 20+ years anyways.)
    If the ducts were sized for the room given then the equipment MUST be sized for what the ducts can handle! Sounds like reverse order.
    Step "C" then "B" then "A"

    You need Static Pressure Readings!

  8. #7
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    Quote Originally Posted by teddy bear View Post
    Outdoor dew points in FL are about 70^ lately. With a vented attic, expect attic dew points that high or higher. Anything colder than 70^F will drip. You have covered your ducts with breathing insulation that is without a vapor barrier on the warm damp side. Moisture with move through the insulation and condense on the damp side of the cold duct. The duct may be less than 55^F. Is there any question about the what may happen. You need to insulate the ducts with a vapor barrier on the warm damp side. The vapor barrier must be above the dew point of the air.
    The lower that you set the indoor temperature, the more insulation that is needed to keep the vapor barrier above the warm, damp air in the attic.

    Now what!

    Warm the indoor temperature as much as possible. Most live with 75^F setting. You need a 45^F cooling coil temperature to get adequate dehumidification from your a/c. The air leaving the coil will be 53-55^F with a 75^F, 50%RH return. You see the problem is that you end up with a 55^F duct temperature.

    If you are unable to place a vapor barrier over the insulation surrounding the cold duct. Other tricks are used. On contractor with several homes with the problem, closed the attic vents and dehumidifier the attic down to 55^F dew point. This stopped all condensation problems in the attic. Also, consider allowing some warm air to by pass the cooling coil that will warm the supply air temperature enough to reduce condensation point in the area of the home with condensation problems.

    As search for real comfort in your home with out condensation problems on ducts and in the exterior walls during the seasons of high outdoor dew point, you will want to be able to control the indoor %RH to <50%RH evening and during rainy weather. During hours of low/no sensible cooling loads and high outdoor dew point, you need supplemental dehumidification. This done by installing a small whole house dehumidifier that injects warm dry air into the cold air supply duct down stream from the cooling coil. Of course the warm air warms the duct when the a/c is not needed and dries the damp side of the duct. Also the fan on the dehumidifier is operated during the cooling hours which also warms the supply duct temperature several degrees, which decreases the condensation problem.
    Many builders in high dew point green grass climates doing this to all of their homes. I suggest investigating units like the ULtra-Aire which has been doing this with +25 years and are made in Madison WI.

    Looking forward to your and the contractors opinion.

    Regards Teddy Bear

    Current dew points These are common in all green grass climates.
    The insulation they covered the ducts ducts in was white on one side and foil on the otherside and they taped every seam with silver tape. After the ceiling was up insulation was blown on top of everything, including burying the ducts. I believe the foil provides an unbroken vapor barrier on the warm side.

    I could absolutely believe the problem is that the ducts got too cold, once we put in the new system they ran the AC down to 72 permanently and then the dripping started, before that there was no dripping but the old system couldn't get it down to 72. (Tenants live in our house, we live in a condo.) Unfortunately I just found out the new tenants expect to run it to 73-74 during the day and 68-70 at night. We personally keep our condo at 75. So I can't force the to turn up the AC.

  9. #8
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    Quote Originally Posted by dan sw fl View Post
    Specific Model numbers are required to verify ID it is a matched system.

    What do the air balancing and commissioning reprts indiciate?

    Dip Switch Settings _________

    Total Air Flow Rate Measured _ _ _ _ CFM

    Total External Static Pressure ( TESP) _0. _ _ " W.C.
    ___________ Supply Side ________ _ 0._ _
    ______________ Return Side _____ _ 0._ _ " W.C.

    Supply Air Temp. ___ 'F
    Return Air Temp. ___ 'F

    ... for starters

    https://www.energystar.gov/ia/partne....pdf?5ace-789f
    RBHP21J11SH2 and RA1636AJ1NA

    I promise you there were no reports done before or after work down here. I don't think anyone realizes that no one is south florida is going to do any reports no matter how much you ask. They just eyeball up your house and oversize the equipment. It took an act of god to get even one company to use rigid metal ducts as opposed to flex ducts and we paid over double to have that done and we had to tear out the ceilings. 99% want to use flex, poorly. I would have to drive to the house to look at the dipswitch settings (we live in a condo 40 miles south and rent our house out) so I will do so tomorrow. I also promise no temperature readings were taken, they got out of there as fast as possible after changing the equipment, I wasn't sure it even worked until 24 hours later it took so long to cool the house down (but once it was cool it stayed, unlike before.) I got so many quotes on both of these jobs its ridiculous. No one will spend one extra minute on any of those things you ask and I have no idea of how to get them for you. The ductwork people didn't even pull a permit.

  10. #9
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    Quote Originally Posted by pecmsg View Post
    If the ducts were sized for the room given then the equipment MUST be sized for what the ducts can handle! Sounds like reverse order.
    Step "C" then "B" then "A"

    You need Static Pressure Readings!
    Who would I have to pay for those, no company down here is going to do that as part of a job. Its just not happening. South Florida is a whole nother world. I asked and the most I got from anyone is a handheld ductolater (sp?) where he pretended to size everything. Only 2 companies would even bid the metal duct job. All the others just wanted to do flex. 100% of companies wanted to upsize my equipment for literally no reason. It was only because I knew from here not to let them, I figured the safest thing to do was keep identical equipment so that's what I argued for. And it kinda worked, the house didn't get oversized equipment and it still cools to at least 72 degrees.

    People also get angry down here when their house won't cool 2 degrees in an hour or less, they *expect* oversized equipment. Our house won't do that, it takes time to drop the temp.

  11. #10
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    You the homeowner pays one way or another.
    Youíve invested a lot of money over several years and still have issues.

    Static Pressure Readings will tell you / them whatís going on!

  12. #11
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    Quote Originally Posted by pecmsg View Post
    You the homeowner pays one way or another.
    Youíve invested a lot of money over several years and still have issues.

    Static Pressure Readings will tell you / them whatís going on!
    I think what Iím trying to say is no one is selling that in south florida so I canít even buy it.

  13. #12
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    Iím in the process of replacing my roof. Iíve gotten 3 written quotes and to verbal. With the information Iíve received I wrote a Scope of Work detailing what I want and requirements. (Specificity fall protection) I then requested a second bid. All 3 went up but there much closer together. The other 2 havenít responded back.

    Any contractor will do what you want as long as your specific. Yours is easy, a simple static pressure test. If they donít want your money fine. Iím sure thereís contractors that have the training and equipment too do one.

  14. #13
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    Quote Originally Posted by pecmsg View Post
    Iím in the process of replacing my roof. Iíve gotten 3 written quotes and to verbal. With the information Iíve received I wrote a Scope of Work detailing what I want and requirements. (Specificity fall protection) I then requested a second bid. All 3 went up but there much closer together. The other 2 havenít responded back.

    Any contractor will do what you want as long as your specific. Yours is easy, a simple static pressure test. If they donít want your money fine. Iím sure thereís contractors that have the training and equipment too do one.
    I used to live up north so I understand what you are saying. I'll tell you about my last 2 months. I need the floor tiled in my condo and we were willing to move out for a month (its 1015 sqft) so they could remove the tile and reinstall it. We called 12+ of the highest rated tile people in south florida. 9 ignored us. 1 came out for a quote but never sent one. Another had us send pics and scope of work instead of coming out, then never sent a quote. One guy said "$12/sqft for labor only" over the phone but wouldn't even put that in writing and wouldn't guarantee it would be done in one month from start to finish. We literally did not have a budget (the owner is paying and she really doesn't care) but you literally cannot pay someone to take this job right now.

    When I got the ductwork replaced I called over 10 highly rated companies and only 2 would come out. All the others were insistent on doing flex duct only. The two that came out, one said "$1000 per drop" and I said "can i have that in writing" and he said "write down on a piece of paper, $1000 x 10, there you go." He clearly was trying to blow me off. The other got the job. 0 of 10 would do ANY of the reports you asked for, and again, these were all highly rated companies - if this is what 5 star gets you, imagine calling 2 or 3 star.

    I do not live in the normal US, I live in south florida. If you tell a contractor how to do their job, they leave and do not come back, you will not even see their eyes rolling because their back will already be turned. There is no shortage of work for them at whatever price they want to charge. If your mainline backs up no one will unclog it for under $400. In return, we have great weather 9 months out of the year.

    Maybe there is a contractor on here that works in Boca Raton - point them to this thread, tell them the job is just off of Palmetto Park exit, and I will pay them whatever they normally charge for these reports. The house is vacant and they can come tomorrow or any day they want, any time they want. If you are a contractor that wants this job, please just reply to this with your price and what time you are showing up and I will pay you.

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    Have the contractor increase the blower speed/CFM.

    Could also be the insulation of the ceiling can is loose and sweating.
    '
    Does the tenant have an aquarium near the area with condensate?

    Is the area near the bathroom?
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    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  16. #15
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    Quote Originally Posted by beenthere View Post
    Have the contractor increase the blower speed/CFM.

    Could also be the insulation of the ceiling can is loose and sweating.
    '
    Does the tenant have an aquarium near the area with condensate?

    Is the area near the bathroom?
    The CFM could be increased but I am under the impression this will increase the humidity level in the house, but I am not opposed to it, and am pretty sure it is not on the high speed right now.

    There was no aquarium and no pets. There was nothing weird like a lot of plants or something that would add additional humidity. The windows are mostly older though so there is probably high infiltration from outside in south florida. I will measure the humidity for several days indoor this week.

    It was one drop past the full bathroom drop. That main trunk on that side of house went bedroom, bathroom, bedroom, and the last bedroom was the one this is happening at (it is the wall between the bathroom and the bedroom.) Are we thinking moisture could be getting into the ducts from the bathroom? I recall it is a 4" drop I think into the bathroom, very small, maybe 3"? 40 sqft bathroom, bedrooms are 144 sqft. (There is a new, fairly large fan in the bathroom that should be getting run, that is ducted to the outside, when the shower is on, etc.)

  17. #16
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    With them keeping it at 72/73 doubt they will have much increase in indoor humidity.

    Not thinking moisture getting into duct. But maybe they aren't running the bathroom exhaust fan long enough. Or, the duct for the bathroom exhaust fan came off, putting a large amount of moisture in the attic right at the area that is sweating.
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    Ok, so I looked through my phone, and when I was double checking the ducts before they closed everything up I actually looked at this one through the ridge of the roof (again the roof was off) and saw they did a horrible job, and made them redo this one. So this picture is from *before* they rewrapped the supply box. The faint red arrow in the top right is point to almost exactly where the water spot is in the ceiling, right up against the wall (you can find of make out the wall in the picture, it is dark though. And this is obviously way before this duct got buried in 1.5ft of blown in insulation (we will see if anything was missed when the ceiling is opened for this job, but again, I personally inspected as much as I could and it looked good to me.)



    You can see stain currently, right at wall:


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    May have rubbed through.
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  20. #19
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    Quote Originally Posted by beenthere View Post
    With them keeping it at 72/73 doubt they will have much increase in indoor humidity.

    Not thinking moisture getting into duct. But maybe they aren't running the bathroom exhaust fan long enough. Or, the duct for the bathroom exhaust fan came off, putting a large amount of moisture in the attic right at the area that is sweating.
    That is a good idea about the duct coming off bathroom fan...I will check that when I am there tomorrow.

    I once had a house in PA that the bathroom fan exhausted into the attic for years with absolutely no problem, unknown to me. Wild how low the humidity is up there and how much a huge attic helps.

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  22. #20
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    Are you saying that your ducts are covered in insulation? If so, Iíve always heard condensation can form on the exterior side of the duct during the summer, causing the ceilings to become wet.


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