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high indoor humidity in summer after replacing attic fiberglass batts with celluose insulation


Location: New Jersey
Month of year: May-June
Outside Humidity levels: 70-90%
Outside temps: 80-90 F
Inside Humidity levels: 59-69% (AC on)
Inside temp : 71 (AC on)

I recently replaced all my ALL of my attic fiberglass batt insulation with blow in cellulose. Since the completion of the job I am noticing that the indoor relative humidity levels in the house are around 10% higher than they were with the fiberglass batt insulation. I am thinking this is happening because the class 2 vapor retarder (batt insulation kraft paper) is no longer there to slow down the diffusion from the attic. Do you folks agree? If so, should I paint the ceilings of the house with a vapor retarder paint (permeability=0.6) that Glidden and sherwin williams are selling? Or should I add another 2 coats of regular latex ceiling paint to the already painted ceilings? Right now I am running 2 extra dehumidifiers in the house in addition to the AC to keep the humidity levels in 52-57% range but they are very noisy and spit out hot air back in the house..


  • KC_JonesKC_Jones Posts: 4,117Member
    Did you add R value with the insulation replacement? If so my guess would be you have basically made the AC over sized compared to what it was before. It now runs less so you get less de-humidification from the system due to shorter run times. If you have a multi speed blower on the system you could try having it re wired to a slower speed which would help with lowering humidity, that is if it isn't already on the lowest speed.
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  • GordyGordy Posts: 9,264Member
    KC makes a good point.
  • tinu2waliatinu2walia Posts: 17Member
    Yes we did increase the attic insulation R value when going to cellulose but I have tried running the AC much longer by basically shutting off registers in the room where the Tstat is and I know that the AC is running pretty long that way, but still it fails to reduce humidity to less than 55% by itself...
  • FredFred Posts: 7,874Member
    How old is the Ac unit? When was the last time it was cleaned/serviced? May be just coincidental that you changed/added insulation and the AC isn't lowering the humidity.
  • tinu2waliatinu2walia Posts: 17Member
    AC compressor and evaporator coil are only 1 yr old and so can't be the servicing issue.
    So, none of you guys think the vapor diffusion through the drywall with the no class 2 vapor retarder in place is causing the higher indoor humidity?
  • SWEISWEI Posts: 7,356Member
    A leaky return duct routed through the insulation has the potential to suck in cellulose litter.
  • GreenGeneGreenGene Posts: 290Member
    I'll leave 2 links that may help, sounds like you have air leakage, you could be leaking around every perforation or fenestration in the attic now, you could be sucking in somewhere on the return.

    Most cellulose manufacturers don't rec'd a vapor barrier with their products but they state if local codes say to do it.
  • GordyGordy Posts: 9,264Member
    edited June 2016
    Is the duct work in the attic? If not then nothing has changed with the duct work from last year when it was functioning exceptable.

    If there is duct work in the attic it may have been josled during the attic insulation Reno making leakage plausible.

    I'm still with the fact KC pointed out about the ac being oversized now.and not getting good deumidification through long run times. Closing off registers will not help this you need flow to all areas to do a decent job dehumidifying.

    Honestly there should NOT have been a vapor barrier on the attic FB batts to begin with in the original installation.
    However that may have helped with leakage that may not have been sealed before, and after the insulation Reno.
  • GreenGeneGreenGene Posts: 290Member
    Agreed, there's not enough info to really diagnose, if you did lower the blower speed as stated it has to be checked to be sure your low side isn't crashing, newer systems have protection with sensors that can tell if the coil is @32 degrees F, dropping the airflow down to 350cfm per ton can help lower humidity by having the air spend more time on the coil, also as stated the system has to be sized right for an cooling system to attempt to control humidity, another issue is set point, residential systems should not be set much lower than 74, it's not a commercial system, the lower the set point the higher your humidity will be, when the air comes off the coil it's humidity is higher because it's colder, as it re enters the room and mixes with the warm air it expands and that lowers RH, if you track it on a psychrometric chart you'll see as the room temp drops the wb db come together and RH goes up, commercial buildings fight this by using reheat.

    Another issue is, are we absolutely sure that before the insulation was changed that they system controlled the humidity better?
  • BillWBillW Posts: 198Member
    I agree with the others that your AC may now be oversized, and not running long enough to dehumidify the space, or that you may have a duct leak. Do you have bathroom fans to exhaust the steam from the showers? How tight are your windows? Is your house under a negative pressure, pulling in outside air? To test, wait until the AC is running. Start the clothes dryer, range hood and any other fans that pull the air out of your home. Next crack open a window, and hold a strip of tissue up to the opening. If the tissue is pulled inward, your house is under a negative pressure, and steps should be taken to stop it. ER/HR ventilators can help, a Heat Recovery ventilator tends to dry the space, while an energy recovery unit balances humidity.
  • Firecontrol933Firecontrol933 Posts: 73Member
    If you want to prove whether the humidity is coming through the ceiling you can try a simple test. If the ceiling surface is smooth enough to take tape, get some painters tape and a length of clear plastic. Tape the plastic to the ceiling for a few hours with the temperature in the home set nice and cool. If after a few hours you don't notice any evidence of moisture between the plastic and the ceiling, I'd say that isn't your problem in the big picture. Not to say you're not getting leakage through the ceiling, just now how you are thinking it's happening.
  • GordyGordy Posts: 9,264Member
    Stack effect is reversed in summer verses winter. So if no sealing was done in the attic before cellulose was blown in then your pulling humidity from the attic into the envelope.

    The video posted shows what should have been done. The benefits are not just in the heating season.

  • GordyGordy Posts: 9,264Member
    Again I will add the Kraft paper on the previous FB batts was probably helping to reduce infiltration.
  • tinu2waliatinu2walia Posts: 17Member
    Thanks for all the replies guys, pls keep them coming. IT is really helping me form a better picture in my mind.
    The consensus so far seems to be that I should NOT put the vapor retardant paint on the ceilings. Can all of you please vote agree/disagree on this point?
  • tinu2waliatinu2walia Posts: 17Member
    edited June 2016
    Now I have found 3 possible theories in all of your responses above. Note that the duct work and the furnace/evap coil is in the attic.
    Theory #1: The return duct now has a leakage somewhere. Is there a way to test this? The main return duct is sheet metal with an insulation jacket around it. There are a lot of flex return ducts going to several rooms. Also attic height/access is really tight. So, it is hard to tell visually if there is a leak.
    Theory #2: The attic was not airsealed properly. Well the contractor charged me for arisealing (including airsealing the recessed lights), but since the attic is not easily accessible in most areas I don't know if he did it right. I have to assume he did not. However, it shouldn't be any worse airsealed than it was with the batts. Right?
    Theory #3: AC not running long enough. Now I did not close all the registers to make the AC run longer. I only closed 1 (the one closest to the Tstat) out of 4 registers in the area where the Tstat is. The Tstat is the Lennox iComfort touchscreen and my AC guy just asked me yesterday to put it on HIGH dehumidification setting with 50% desired value to reduce the airflow in the system and see if that helps. I did that but need a few days to figure out if it works... The dehumidifiers were still running this morning at 55% setting so my guess is it is not working too well.

    I would like to test the return duct leakage theory if someone can tell me an easy way of doing it. Is there a way to harmless create colored smoke which I can create near each return in each room and then see if I can see that colored smoked leaking in the attic??
    I will also test the ceiling diffusion test with the suggested plastic taping approach...

    Thanks everyone for there suggestions, please continue helping me figure this out....
  • GordyGordy Posts: 9,264Member
    edited June 2016
    My bet is the ductwork took a beating during insulating recon.......
  • JUGHNEJUGHNE Posts: 5,729Member
    Yep, anything like an air handler or piece of ductwork is fair game for insulators. Those items were put there for them to sit on. I would look at your furnace filter and see if you have any insulation dust on it, assuming there was none before. A lot of hidden attic flex duct might be just stuck together with duct tape, works awhile......and I will never see it again.....I'm done!
    So it takes little movement to disturb what used to work.

    How many Sq feet was the attic space that he sealed and how long did it take to seal those leaks. Some "seal" leaks from the end of the blower hose as they believe the insulation will seal air flow cracks.
  • GordyGordy Posts: 9,264Member
    Especially if the old insulation was removed.
  • tinu2waliatinu2walia Posts: 17Member
    They supposedly sealed 1900 sq ft attic in 1.5 day. Many of the recessed cans I could see were not sealed properly and I told them to fix them and they did. The sealed the recessed cans with custom made reflectix cylinders with orange foam at bottom and openings. I could not see several recessed cans so can't say if they sealed them properly. But that can not be the issue because with the batts insulation, there was several inches of gap between insulation and cans and there was no insulating hats on the cans. So the recessed cans are in a better shape air leak wise than before. I did see spray foam around pipe openings, near chimney and some top plates. Don't think they sealed fan boxes or all the top plates. But again, those things were not sealed when we had fiberglass batts either. So, air sealing wise I don't think we are any worse than before, probably a little better.

    I am getting a strong feeling that the ducts have been compromised by the insulation guys but have no idea how I will find and fix the leak in the ducts given that they have put 15 inch cellulose in 95% of the attic.

    I will check the furnace filter tomorrow to look for cellulose in it, but can't see how I will be able to find the leak in ducts if any. The main return duct is only 30% accessible, the rest has 15 inches of cellulose around it and it will be hard to go near it. The flex return ducts are all over the place burried in 15 inch cellulose, so there is no way for me to go after each of them..

    Anyways, the first step will be to check the filter, so let me do that tomorrow morning. Will report the finding....

    Thanks a ton for your continued help....
  • BobCBobC Posts: 4,965Member
    That is going to be a filthy job.

    One thing that might work is closing all the registers and turn the AC on. That should over pressururize the duct system and make it possible to feel the air leaks. Check the supply ducts and any return ducts in the attic

    Make sure you wear a good respiratory mask and good luck.

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  • hot_rodhot_rod Posts: 11,633Member
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  • JUGHNEJUGHNE Posts: 5,729Member
    There are (or used to be) safe smoke candles/bombs you would put into a firebox to see if the colored smoke showed up thru your supply registers.
    If you placed one in your return duct, closed all supply registers and ran the air handler on fan only and checked the attic for smoke, this would maybe show leaks in the supply side. This may give you a visual aid for BobC's recommendation.

    The return side though might only show up with insulation on the inlet side of the filter if the filter is actually on the air handler.
    If you have filter grills (in the living space) then you may never see the insulation.

    There are cameras that can travel down sewer pipes.....but flex duct????

    I would guess crawling around in an attic that size for 1.5 days might get most cracks.....but I would have certainly sealed the cans the owner could see. ;)
  • GordyGordy Posts: 9,264Member
    hmmm if it's the return that air would be delivered over the coil for conditioning. If it is the supply that already conditioned air would pick up humidity in the delivery. Not that a leak in the return is okay. If the return is rigid duct, and not flex most likley it would be okay........maybe.
  • JUGHNEJUGHNE Posts: 5,729Member
    edited June 2016
    So you think that pressurized supply air could gain humidity from the attic?? Hard to wrap my head around that one.
    I could see reduced capacity by air loss to the attic causing less dehumidification in the conditioned space.

    I hate insulated attics and flex duct. Always tried to get a good seal at connections....probably the slowest flex installer in the area. Even built catwalks over air handlers and flex duct to prevent the big foot adjustments. Everyone knows where I live and if things happen in the attic like this my phone will ring.

    Note: question for homeowner....can you see the condensate drip from the coil. Is there more than there used to be??
  • GordyGordy Posts: 9,264Member
    edited June 2016
    No but I see hot humid air infiltrating the supply ducts in the off time, filling the ducts. ,remember stack effect is reversed in summer. So now your pulling air in from the attic. The air sealers forgot the ducts.......
  • JUGHNEJUGHNE Posts: 5,729Member
    Yes Gordy, I see your point, homeowner might on a hot humid day check temps of air gravitating out of supply registers, with system off. Turning on clothes dryer and all exhaust fans may help locate the leaker in this case.

    Sealing ducts are probably not in their job description. Seriously the duct system should be included in attic sealing. Perhaps a licensing issue. But the energy pros could capitalize on this situation by including this in their attic improvements.
    If they remove or temporarily move the old insulation for sealing the ceiling leaks that would be the ideal time to repair any old flex leaks. We all have seen (or didn't want to see) some faulty flex connection buried in insulation.
  • GreenGeneGreenGene Posts: 290Member
    edited June 2016
    Yeah, if the return is in the attic and compromised could be a real problem, still looking at your stats 80-90 outside and 71 inside is too cold, 74 should be plenty, the lower you set it the higher the RH will be.

    from the book:

    "Relative humidity (RH) is a function of both the moisture in the air and the air temperature. It is equal to the amount of moisture in the air relative to the amount of moisture the air could hold if it were 100% saturated (e.g., fog). Air that has a relative humidity of 50% has 50% of the moisture it can hold at that dry bulb temperature. Therefore, relative humidity can be lowered by either decreasing the moisture in the air, or raising the air temperature."

    What tends to happen is people aren't comfortable and the first thing they do is lower the set point to be colder, they just made it worst and you're creating a mold farm and other health issues crop up when you are out of the 40-55% RH range.

    If you can't control RH at @74 something is really wrong, usually it's over sized, infiltration.

    My house for example is a raised ranch, the lower level is finished off and exposed to the upstairs from an open central staircase, being a raised ranch the lower level is half in the ground, built in 71, I know it's not to todays standards, I have to run a dehumidifier down there from May-Oct and keep it @ 50% and I have no cooling down there, I have 2 central returns 1 up 1 down and I have 2 supplies on either end of the lower level at @75cfm each just to move the air around the house, not to cool the downstairs.
  • tinu2waliatinu2walia Posts: 17Member
    So, I checked the furnace filter this morning. Very little cellulose on the bottom ridge of the 90 day filter. Other than that it was very clean. The main return duct looked solid, I could see 5 flex ducts from distance hooked on to the main duct with the inner pipe tied securely to the starting collars. The outer insulation sleeve was hanging somewhat but that should not matter...
    Just found a 3/8 dia hole in a starting collar I could reach. My guess is that the very little cellulose I found in the filter went in from that hole... Could be more holes in other starting collars, but again, they have always been there....
    Since there was little cellulose in the filter, I am assuming there is no major leak on the return side.
    I personally don't see how a leak on the supply side can continuously pump in humidity when the AC is on most of the day. What I see is that on a humid 85 degree day, when the AC is running for hours, the humidity level does not decrease much at all and many times increases (as GreenGene points out, cooler air will have higher RH if the moisture content is the same).
    I find 74 degree rather uncomfortable personally but have now set the Tstat to 72(present mode)-75(away mode). If I set it too high in away mode (like 78), AC will not run much in the away mode and a lot of humidity till build up...

    JUGHNE : There was no visual condensate drip from the evap coil into the secondary drain pan. The evap coil has a working drain connection, so the water might be going in the drain. Also, last night, temp was only 58 in NJ so AC did not run much (if at all). Could it be that the evap coil is not condensing enough water (It is a 2 stage compressor)?? But if the AC can cool the house to 71 or less (if I wanted to) then the evap coil must be cold and must be condensing water. Right? And if the AC is running for hours then that should reduce the humidity unless more is getting in from the return leaks or diffusion or other leaks in the ceiling...

    I will be performing the condensation test for vapor diffusing through ceiling as suggested by Firecontrol933 when it gets hot an humid again, For now we have a cold front in NJ.
  • GordyGordy Posts: 9,264Member
    edited June 2016
    My best guess if the system performed to your expectations last summer under similar indoor/outdoor temps, and humidity levels. You have to look at what changed, and what changes could affect other things.

    In your case a major change was the insulation Reno. From there we know duct work is in attic. We also know that taking insulation out, and putting insulation in plus air sealing things got moved. How much big ?

    Is it possible the AC took a dump, and is not giving maximum performance? Have to rule that out. I think I would cover that before mulling around in attic insulation looking for leaks.
  • Paul48Paul48 Posts: 4,492Member
    Notice anything different when you open the front door? Is the door sucked in? Do you get a blast of warm air in your face?
  • bnjmnbnjmn Posts: 32Member
    How long has it been since the new insulation was installed? My experience is that cellulose is installed somewhat damp or wet. I could see humidity levels being higher while that dries out.

    Just a thought
  • GordyGordy Posts: 9,264Member
    Yes usually with cellulose pack insulation in walls. Not for attics.
  • njtommynjtommy Posts: 1,102Member
    What type of thermostat do you have controlling the system?
    You maybe able to lesson the number of cycles per hour to limit cycles and also keep it running longer.
  • tinu2waliatinu2walia Posts: 17Member
    edited July 2016
    Sorry for the impasse on this thread for several weeks. I apologize, we had a death in the family and were in a phase of mourning. I just now was able to restart investigation on this and have figured out the problem. It has nothing to do with the cellulose insulation as many of you had guessed and all to to with the AC. The root cause seems to be the stage 1 of the 2 stage XC 16 Lennox compressor that was installed last year. I have the Lennox iComfort touch screen Tstat which shows humidity levels. I monitored the systems closely for several hours yesterday (outside humidity was around 80% and outside temp was around 78). What I observed was that when the Lennox XC 16 compressor kicks in, it runs for 15-20 minutes in stage 1. It is in those 15-20 minutes, the AC systems continually spits out damp air and the indoor humidity rises at about 1% a minute in those first 15 minutes. After that, it seems like the compressor's stage 2 kicks in and the humidity stabilizes to about 63% for about 2-3 minutes and then it starts decreasing again around 1% about 2 minutes until it again stabilizes around 48%. Then after a while AC stops. Things are stable and humidity does not increase when the AC is stopped. Then the AC kicks in again in stage 1, and immediately the humidity starts increasing again for 15 minutes. Then stage 2 kicks in and it starts going down... And the cycle continues.

    So, the problem clearly is that in stage 1 of the compressor the evap coils are not getting cold enough but being horizontal flow they are staying wet from the previous run and thus as long as the AC runs in compressor stage 1 the circulated air keeps getting damp from the water in the coils. That is my theory. Then when stage 2 kicks in the evap coils become sufficiently cold and the circulating sir loses water in the cold evap coils and indoor humidity drops again.

    The above theory has been empirically validated by observing the Tstat continuously for several hours yesterday.

    The question now becomes how do we fix it. Does anyone know if the Lennox XC 16 compressor can be forced to always run in stage 2 and bypass stage 1. I have the iComfort touchscreen Tstat. Can that control the run time of stage 1 of the compressor (and basically shorten it to 0-1 minute??)

    I am thinking I must not have noticed the humidity increase last year because the baseline indoor humidity might have been lesser last year or probably because the AC was installed in last Aug and perhaps there weren't enough high humidity days for me to notice that....
  • GreenGeneGreenGene Posts: 290Member
    2 stage systems are supposed to control humidity better.
  • GreenGeneGreenGene Posts: 290Member

    Lennox supposedly has a guide for setting the system up but I can't find it, the high end thermostats are supposed to sense humidity and some can slow the blower speed and switch between stages if set point is close to being made but RH is still high.

    On some commercial units we can order a hot gas bypass option that will bypass hot gas from the compressor to the evap and have it heat the air to dry it.

    You'll have to find all your info, outdoor unit, indoor unit, tstat, install/service manuals and see if any options exist.
  • GreenGeneGreenGene Posts: 290Member
    icomfort is supposed to control humidity

    check the setting
  • GreenGeneGreenGene Posts: 290Member
    edited July 2016
  • tinu2waliatinu2walia Posts: 17Member
    edited July 2016
    Regarding the iComfort Dehumidification settings. I had already tried that putting it to high & medium. Outdoor unit is non communicating and furnace is not lennox. So it can only do so much. It was not able to reduce humidity levels to <=55 on humid days. Main reason seems to be that stage 1 is dumping too much moisture in and then stage 2 has to work harder to remove it...

    I did find the installers Tstat manual and even tried setting the second stage delay timer to just 5 minutes hoping to reduce the stage 1 run time. But that did not work either. The AC is not even listed in the Tstat under equipment. Looks like because the furnace is non lennox, they used a interface control module to run the furnce and compressor. that is why it seems like stage delay Tstat timer change did not work.

    My AC guy has just told me to install a jumper cable between y1 & y2 terminals (blue and yellow wires) on the outdoor unit to bypass stage 1. In marketing material the stage 1 is better at humidity control but in my situation stage 1 is actually increasing the moisture levels 14-15%. It is either not cooling the coils enough or in my situation with a horizontal flow furnace in the attic, it just does not work. Tying Y1 & Y2 together and bypassing the stage 1 will tell me quickly if my theory is right. Will post an update once that's done....
  • GreenGeneGreenGene Posts: 290Member
    you have a mismatched system

    it isn't going to work

    I'm beginning to think it's sized wrong too, has to be
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