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  1. #1
    Join Date
    Jan 2012
    Posts
    27

    Flex Ducts sealing. Aeroseal - good idea? bad?

    hi all. so after browsing these forums for a week i still couldn't find the exact solution to my ongoing problem. so i figured i'd start a thread.

    i'm going to be as detailed as i can.

    my house was built in 98. i've lived in it since 05. the house is a single story with 4 bedrooms, 2 bath, garage. its about 1500 sq. ft. located in Phoenix, Arizona. the AC unit is outside and i have an air handler up in the attic. the AC unit was replaced in 04, before i bought the house.

    now here's my problem: about half of the registers in my house have poor air flow coming from them with a lot less cooler temperature (in the summers) than the other half. my air handler is situated towards the front of the house (from the garage side). that half of the house has 3 smaller bedrooms and a bathroom. those registers blow very hard with cold air. the rest of the house, as you walk towards the end of it from the garage, has a living room, a kitchen and a master bedroom with its own bathroom and a walk in closet. all those registers blow very poorly and with a lot warmer temps than the ones toward the front of the house.

    i had a guy come out a few months back to check my AC unit. they looked at the coil and said it was clean. they cleaned it anyway though just to be sure. they tested the freon pressure and the temp straight out of the AC and said that was all normal. they used a laser to measure the temps coming out of the registers at the front of the house and the temps were normal (i dont remember the exact temps), but the back of the house registers were at least 10 degrees highter (in the 70's somewhere).

    the guy said that i most likely have leaking ducts, which i suspected from the beginning. also, the registers have dust trails on them in all rooms, not just the ones that blow poorly. me and him climbed up into the attic to take a look and the crawl space is very, very small. you literally have to crawl on your stomach over the beams and over the loose insulation that covers the entire floor of the attic.

    the ducts are not metal like in some homes, but are huge flexible tubes that run all over the attic and really look like a big headache for me to try to do anything with them, let alone try to determine where each one leaks. they looks like tentacles on a kraken for the lack of better explanation.

    i have a friend that works for a company that "greens" up the homes. he's a reliable guy and he said that they could Aeroseal my house for $1200.

    now, from reading on these forums and researching online, my understanding is that Aeroseal is really ideal for aluminum ducts and not flex ones. please, correct me if i'm wrong. or should i consider replacing the ducts maybe? or maybe its not even the ducts?

    with all that said, i would greatly appreciate any suggestions, comments, and/or solutions.

    thank you so much!

  2. #2
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,058
    Quote Originally Posted by konoplya View Post
    hi all. so after browsing these forums for a week i still couldn't find the exact solution to my ongoing problem. so i figured i'd start a thread.

    i'm going to be as detailed as i can.

    my house was built in 98. i've lived in it since 05. the house is a single story with 4 bedrooms, 2 bath, garage. its about 1500 sq. ft. located in Phoenix, Arizona. the AC unit is outside and i have an air handler up in the attic. the AC unit was replaced in 04, before i bought the house.

    now here's my problem: about half of the registers in my house have poor air flow coming from them with a lot less cooler temperature (in the summers) than the other half. my air handler is situated towards the front of the house (from the garage side). that half of the house has 3 smaller bedrooms and a bathroom. those registers blow very hard with cold air. the rest of the house, as you walk towards the end of it from the garage, has a living room, a kitchen and a master bedroom with its own bathroom and a walk in closet. all those registers blow very poorly and with a lot warmer temps than the ones toward the front of the house.

    i had a guy come out a few months back to check my AC unit. they looked at the coil and said it was clean. they cleaned it anyway though just to be sure. they tested the freon pressure and the temp straight out of the AC and said that was all normal. they used a laser to measure the temps coming out of the registers at the front of the house and the temps were normal (i dont remember the exact temps), but the back of the house registers were at least 10 degrees highter (in the 70's somewhere).

    the guy said that i most likely have leaking ducts, which i suspected from the beginning. also, the registers have dust trails on them in all rooms, not just the ones that blow poorly. me and him climbed up into the attic to take a look and the crawl space is very, very small. you literally have to crawl on your stomach over the beams and over the loose insulation that covers the entire floor of the attic.

    the ducts are not metal like in some homes, but are huge flexible tubes that run all over the attic and really look like a big headache for me to try to do anything with them, let alone try to determine where each one leaks. they looks like tentacles on a kraken for the lack of better explanation.

    i have a friend that works for a company that "greens" up the homes. he's a reliable guy and he said that they could Aeroseal my house for $1200.

    now, from reading on these forums and researching online, my understanding is that Aeroseal is really ideal for aluminum ducts and not flex ones. please, correct me if i'm wrong. or should i consider replacing the ducts maybe? or maybe its not even the ducts?

    with all that said, i would greatly appreciate any suggestions, comments, and/or solutions.

    thank you so much!
    It is not designed for flex.

  3. #3
    Join Date
    Mar 2011
    Location
    Galveston Texas
    Posts
    530
    aeroseal isn't designed for flex duct.

    You could have one of a cpl of things wrong with the system.

    1: Leaking ductwork
    2: improper placement of the ducts on the plenum
    3: improper sizing of the ducts through out the house
    4: choked off or smashed ductwork

    While it's still cool out, have your A/C guy come back out and take a look at the ductwork, and the layout in general and make sure everything is sealed correctly and properly place through out the house.

  4. #4
    Join Date
    Dec 2003
    Location
    Citrus County, Florida
    Posts
    1,491
    My question is how long Aeroseal will last until it needs to be redone. I personally feel that mastic is the way to go as it is permanent.
    Doug

  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,776
    BradBrenner, this is the Ask Our Pro's forum, and only Pro members that have been vetted by the AOPC may post advise here. Please apply to the AOPC today, thank you.

    You can find the rules for posting and qualifications here.




    Further infractions may result in loss of posting privileges.
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  6. #6
    Join Date
    Dec 2011
    Location
    PA
    Posts
    98
    Quote Originally Posted by konoplya View Post
    hi all. so after browsing these forums for a week i still couldn't find the exact solution to my ongoing problem. so i figured i'd start a thread.

    i'm going to be as detailed as i can.

    my house was built in 98. i've lived in it since 05. the house is a single story with 4 bedrooms, 2 bath, garage. its about 1500 sq. ft. located in Phoenix, Arizona. the AC unit is outside and i have an air handler up in the attic. the AC unit was replaced in 04, before i bought the house.

    now here's my problem: about half of the registers in my house have poor air flow coming from them with a lot less cooler temperature (in the summers) than the other half. my air handler is situated towards the front of the house (from the garage side). that half of the house has 3 smaller bedrooms and a bathroom. those registers blow very hard with cold air. the rest of the house, as you walk towards the end of it from the garage, has a living room, a kitchen and a master bedroom with its own bathroom and a walk in closet. all those registers blow very poorly and with a lot warmer temps than the ones toward the front of the house.

    i had a guy come out a few months back to check my AC unit. they looked at the coil and said it was clean. they cleaned it anyway though just to be sure. they tested the freon pressure and the temp straight out of the AC and said that was all normal. they used a laser to measure the temps coming out of the registers at the front of the house and the temps were normal (i dont remember the exact temps), but the back of the house registers were at least 10 degrees highter (in the 70's somewhere).

    the guy said that i most likely have leaking ducts, which i suspected from the beginning. also, the registers have dust trails on them in all rooms, not just the ones that blow poorly. me and him climbed up into the attic to take a look and the crawl space is very, very small. you literally have to crawl on your stomach over the beams and over the loose insulation that covers the entire floor of the attic.

    the ducts are not metal like in some homes, but are huge flexible tubes that run all over the attic and really look like a big headache for me to try to do anything with them, let alone try to determine where each one leaks. they looks like tentacles on a kraken for the lack of better explanation.

    i have a friend that works for a company that "greens" up the homes. he's a reliable guy and he said that they could Aeroseal my house for $1200.

    now, from reading on these forums and researching online, my understanding is that Aeroseal is really ideal for aluminum ducts and not flex ones. please, correct me if i'm wrong. or should i consider replacing the ducts maybe? or maybe its not even the ducts?

    with all that said, i would greatly appreciate any suggestions, comments, and/or solutions.

    thank you so much!
    Based on what I have read you have possibly one or all of the following:
    1.) Improper duct sizing
    2.) No dampers
    3.) crushed supply duct
    4.) Improper placement of the take-offs on the plenum/trunk line

    The reason for using the flex in your application is because it is insulated and will not sweat like hard duct will. Do you have a larger flex duct that the smaller ones run off of?

  7. #7
    Join Date
    Jan 2012
    Posts
    27
    Quote Originally Posted by JonesHVAC-R View Post
    Based on what I have read you have possibly one or all of the following:
    1.) Improper duct sizing
    2.) No dampers
    3.) crushed supply duct
    4.) Improper placement of the take-offs on the plenum/trunk line

    The reason for using the flex in your application is because it is insulated and will not sweat like hard duct will. Do you have a larger flex duct that the smaller ones run off of?
    i think the ducts are all the same size, to be honest. it was very hard to tell looking towards the back of the house from climbing into the attic. its pretty dark there and the whole space pretty much is clustered up with the ducts.

    what are dampers and plenum? i'm very clueless when it comes to the hvac topic.

    thanks for the reply.

  8. #8
    Join Date
    Dec 2002
    Location
    Arizona
    Posts
    4,341
    Quote Originally Posted by JonesHVAC-R View Post
    Based on what I have read you have possibly one or all of the following:
    1.) Improper duct sizing
    2.) No dampers
    3.) crushed supply duct
    4.) Improper placement of the take-offs on the plenum/trunk line

    The reason for using the flex in your application is because it is insulated and will not sweat like hard duct will. Do you have a larger flex duct that the smaller ones run off of?
    We have a winner! You need a room x room Manual J done and THEN a Manual D done for proper duct sizing. Both APS and SRP have a program to help pay for duct sealing and you can have an energy analysis done for your home for $99.00. I would start there.
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  9. #9
    Join Date
    Jan 2012
    Posts
    27
    Quote Originally Posted by jimj View Post
    We have a winner! You need a room x room Manual J done and THEN a Manual D done for proper duct sizing. Both APS and SRP have a program to help pay for duct sealing and you can have an energy analysis done for your home for $99.00. I would start there.
    thanks for that info. i thought that manual j and d are performed for new built homes to see which size system to put in initially. you're saying that i should probably replace the ducts altogether given these new calculations? i've read SRP's webiste and from what i understand they'll only pay up to $175 for the duct repairs. i will be doing the analysis though very soon, that is a good idea.

  10. #10
    Join Date
    Dec 2002
    Location
    Arizona
    Posts
    4,341
    Quote Originally Posted by konoplya View Post
    thanks for that info. i thought that manual j and d are performed for new built homes to see which size system to put in initially. you're saying that i should probably replace the ducts altogether given these new calculations? i've read SRP's webiste and from what i understand they'll only pay up to $175 for the duct repairs. i will be doing the analysis though very soon, that is a good idea.
    Part of the BPI analysis is duct leakage testing using what is called pressure panning. A room x room Manual J will tell you the air flow that is needed in each room and the Manual D will see that you can get it there. If someone will do these for you ( expect to pay) you will know if yor duct sizing is correct or not, I would bet on not!
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  11. #11
    Join Date
    Jan 2012
    Posts
    27
    Quote Originally Posted by jimj View Post
    Part of the BPI analysis is duct leakage testing using what is called pressure panning. A room x room Manual J will tell you the air flow that is needed in each room and the Manual D will see that you can get it there. If someone will do these for you ( expect to pay) you will know if yor duct sizing is correct or not, I would bet on not!
    thanks jim. are the manuals expensive to conduct usually? what is the ballpark average?

  12. #12
    Join Date
    Jun 2005
    Location
    Near Chicago, IL
    Posts
    3,317
    Quote Originally Posted by konoplya View Post
    now here's my problem: about half of the registers in my house have poor air flow coming from them with a lot less cooler temperature (in the summers) than the other half. my air handler is situated towards the front of the house (from the garage side). that half of the house has 3 smaller bedrooms and a bathroom. those registers blow very hard with cold air. the rest of the house, as you walk towards the end of it from the garage, has a living room, a kitchen and a master bedroom with its own bathroom and a walk in closet. all those registers blow very poorly and with a lot warmer temps than the ones toward the front of the house.

    they used a laser to measure the temps coming out of the registers at the front of the house and the temps were normal (i dont remember the exact temps), but the back of the house registers were at least 10 degrees highter (in the 70's somewhere).

    the guy said that i most likely have leaking ducts
    Big clues here.

    Temperature difference in supply ducting does not mean duct leakage.

    Duct leakage (excluding friction losses) can be 1000 units of air at point A and 800 units at point B.

    Temperature difference means that the ducting is losing or gaining heat.

    Most flex ducting is only R4.2, R6 or R8.

    Ceiling insulation is typically R19 or more, so your supply (and return) flex duct is a really poor insulator.

    You probably also have leakage on the return side, so not only are the flex ducts gaining radiant heat, the air leaks at the connections are sucking in hot attic air.

    You need to either move the ducting into conditioned space, or move the thermal boundary of the building and leave the ducts where they are... or live with it.

    Do NOT seal up the ductwork unless you determine that it is properly sized. At that point, attic return leaks are worse than attic supply leaks.

  13. #13
    Join Date
    Dec 2011
    Location
    PA
    Posts
    98
    Quote Originally Posted by konoplya View Post
    i think the ducts are all the same size, to be honest. it was very hard to tell looking towards the back of the house from climbing into the attic. its pretty dark there and the whole space pretty much is clustered up with the ducts.

    what are dampers and plenum? i'm very clueless when it comes to the hvac topic.

    thanks for the reply.
    My apologies on not getting right back to you, I had a busy week.

    To answer your questions a plenum is the stack of duct coming directly off of the furnace/indoor coil. A trunk line would be what comes off the plenum in either direction. The supplies then come off the trunk line. As those supplies are taken off the trunk line (take-offs) there should be either a mechanical (zoned (multiple thermostats) applications) or a manual damper. A Damper is what restricts or allows air flow to a supply, looks like an inline lever.

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