Discussing Ducts Types and Tips
Vložit
- čas přidán 2. 06. 2024
- Bryan spends some time discussing duct types and tips at the Kalos morning meeting. He talks a bit about the differences between various types of flex ducts and talks about fabricating duct connections.
Timestamps:
00:00 Intro
00:14 Black flex duct vs. silver flex
04:02 Duct sweating
06:53 Preventing duct sweating at connections
08:24 Duct liner best practices
09:14 Vapor barriers
10:30 Panduit straps vs. silver tape
11:51 Contact cement vs. silver tape
13:21 Outward-cinching stapler use
14:26 Overview of tips
15:09 Running flex ducts properly to prevent compression
16:35 Outro
We occasionally come across black flex in Florida, which isn't the same as trailer flex. The black flex is water-resistant and tends to handle moisture a bit differently than a silver flex duct, but it is sometimes erroneously replaced with silver flex or used as trailer flex. The silver flex duct is reflective and tends to reflect heat from the roof decking, whereas the black flex absorbs that heat and results in greater thermal gains inside the duct. Although there is variation between manufacturers, silver flex tends to be a bit more durable than black flex. However, black flex is FAR less prone to sweating than silver flex.
Flex ducts tend to sweat at connections, where the insulation has been compressed, and wherever it touches another surface (like a truss or another duct). Condensation occurs at those locations because they tend to be cooler than surrounding areas (and are more likely to reach the dew point). The ducts and air handlers can also sweat if they're not touching but merely shade one another.
When you're making a connection, make sure you understand that condensation is most likely to occur at that point. Be sure to seal it completely and let the mastic (duct sealant) dry on the collar before applying the outer liner to it. Whenever you must use wet mastic, it's best to keep mastic tape on hand to use as a backup option. It's also worth remembering that a Panduit strap is just a mechanical connection and won't stop leakage.
Compression can also cause duct sweating, so address points of potential leakage and make sure you're pulling the outer lining properly (without bunching the insulation). However, you need to roll the edge of the lining a bit to maintain a vapor barrier on the outside; that vapor barrier must be completely intact to prevent water vapor from making it into the ductwork. The vapor barrier should be against the duct board and not be pulled back or compressed in any way. (Panduit straps can contribute to compression. Silver tape is generally a better option, especially if you use denatured alcohol and apply it smoothly with a tape squeegee.)
Spray glue and other contact adhesives/cement are good for short-term contact, but it dries out and becomes brittle over time. So, we prefer silver tape to contact cement, spray glue, and fab tape. Outward-cinching staplers can be used to attach staple flaps.
Overall, when you fabricate connections, you have to pay attention to the duct type (and material), proper strapping, and how tightly the flex duct is pulled. Having tightly pulled flex duct reduces sweating and turbulence. Ideally, flex duct should only exist in straight runs; we can rely on metal fittings if we need to make an angle.
Read all the tech tips, take the quizzes, and find our handy calculators at www.hvacrschool.com/.
I appreciate the tips. I love adding more knowledge to my arsenal.
Such a legend... When I first started in the trade I credit a lot of what I know to this guy, and to this day he's still putting out great content. Thank you Brian!
Emin HVAC hasn't posted in years but his channel is awesome for the commercial side.
It's Bryan with a y 😉
@@naughtiusmaximus1811 thanks, was wanting to expand my knowledge base
How long have you been in the trade?
This should be mandatory viewing for all HVAC people. I’m about to go repair a bunch of trunk line leaks by using alcohol and tape and mastic and this video just added days to my job because I can’t unsee all the bends and touch points of duct on trusses. I will happily be resolving all these issues knowing that I did them right, once, and never have to deal with them again. Thank you.
Yeah everytime I see ducts through truces I cringe and pull out the hanging strap
I don’t normally do ductwork try to avoid it. But as usual when I watch one of your videos I learn something.
Appreciate the lesson. I'm just a homeowner, but trying to get educated on how to improve my home's energy efficiency, to lower my painfully increasing electric and gas bills. Seems my situation is different because my A/C and ductwork in all in the basement and it's a conditioned space, therefore leaks and condensation probably aren't as much of a factor as they are as when it's all up in a hot humid unconditioned attic. Still, I can use these techniques for optimizing the system.
Very informative as always. Good tips about silver/black duct and best ways to make connections. Really wish there was more about different types than just flex but still good video. I know you have to keep to your market.
Love the channel👍👍👍
Learned slot watching yall
!!!
Keep up the great work
Nice lecture on conduction convection and exhaustion
Thank you for this great video!
When I added straps to my ducts, I put a sleeve underneath the ducts made from cardboard to avoid compression and kinks. Also for each boot, I added some Malco FDS1- Flexible Duct Support to keep a nice curve from the floor. They can be used as well if you have some ducts leaving the plenum at an angle.
Also, if the attic has already a radiant barrier, it doesn't matter if your ducts are black or silver, something to consider. While ducts are part of the system, sealing and insulating the plenum is something to do to help against air leaks and temperature swing.
Great points Bryan. Thank you.
This channel is great. I'm trying to improve my airflow and reduce my air leakage from the homeowner-done hvac job and I have learned a ton. Unfortunately, most of my flex duct is resting on the joists in my attic and I'm not sure there is enough slack to lift it off the joists, but I'm going to try. If that doesn't work, I may be replacing all the ducting as time and money allows.
Very informative such a great teacher
Not planning to have any flexible ductwork in my build, and mostly planning the ducts for ventilation because my next home will be in a region that doesn't need much cooling. But best practice is never wasted!
Awesome training. I’d love to see a tutorial for 4 piecing duct board
Good information, thanks
So, black flex is less likely to sweat in an attic, seems like it does have a silver lining...
I see what you did there
Great content
Great job
Thank you!
Thanks for you work
If you look closely at the foil you will see good flex has reinforced string every 1/4" instead of every 1/2" that some manufacturers use. Reduces rips when moving it around during installation.
Black flex duct in the attic is "less efficient" in the cooling season, but black flex duct in the attic is "more efficient" in the heating season. Correct? What ACCA approved J-manual software addresses the flex duct covering color, which then includes its heat gains or losses?
I bought a house in 2022. The hvac hadn't been updated since house was built in 1996. The ducts had stinky mold so we decided to have new hvac and all ductwork replaced. Hvac system and box shaped sheet metal duct (with insulation inside) trunklines were in crawlspace with flex ducts running off metal trunk line.
We had a small company replace all ducts and complete system.
I was kinda surprised after install when I noticed they didn't use any sheetmetal ducts at all... only flex ducts for the entire system...
Is that normal? Anything wrong with using all flex ducts to replace old metal trunk line?
Thanks!
Thank you
Hey have you ever tested wrapping one pass of mastic tape around the collar which has a little “give” and will act as a seal - and then use the panduit strap which should compress down into the mastic tape. I think I would rather do that then play with mastic inside the collar
I hate to remove it later
Yes, I love installing it that way Joe
That's how I do it
How often do flex ducts have to be cleaned with heppa filter
Why would anyone purposely install a unit into a very hot attic (140/150 F) and expect it to be efficient? System spec’s are most likely being violated! Please explain without sarcasm. Thanks!
Retrofits and remodels. Here in the DC/Baltimore area, brick rowhouses have this all the time, especially high velocity units. It opens the floor/wall space that a closet air handler/furnace takes up. Flippers are mostly about profits more than efficiency. In detached new builds around here with bigger, more open truss attics, that system is usually just for the upper floor zone so any efficiency comes from it not having to condition the entire house, only up there.
what are your thoughts of the Rheia system in Florida?
I don't know, but Rhea Seahorn is great in Better Call Saul.
I never like F/G ductwork. Maybe for a very small systems. I like wrapped metal. In a basement use ridged pipe, then wrapped.
hello, can duct asbest be replacing for flexible duct??
How do I know the maximum airflow, CFM, that can be handled by some 6” flex duct I have in my attic, if I put in a booster fan to be able to increase aire flow at certain times? The duct says 4000 FPM maximum, it’s 6” duct and I’ve got about 15’ of duct run before the booster fan and then 15’ after The dan to the vent? Thanks in advance for any help on this.
Sir how can enroll with your school I want also to learn more about HVAC
I literally clapped when I heard you say flexduct should only be used for straight runs.
Yea nobody does that in the northwest lol. Crazy bends and runs with flex in attics. Kinks all over the place is the norm.
Northeast, land of crawlspace and damp basements. Literally rains off the insulation blanket. Ruins F/G wrap. I love the foil bubble wrap. Now a growing business is crawlspace incapsulation, sealed with dehumidifiers. You can smell the difference in new homes with a incapsulation system installed over homes just a few years old without them sealed and conditioned.
I need to tape up the hole in the top of my furnace which was cut to put the air duct in which goes up into the ceiling and outside. What should I use to tape it up? The duct gets hot. Thank you.
Use 367 tape it
And sheet metal
Thank the lord for sheet metal in basements
Why should you not use silver duct under a manufactured home?
Pretty sure the black stuff for trailers are thicker material that can lay against water and the ground. Silver stuff is more easily torn through by critters and tears more easily when laying against the ground.
👍🏻
Metal ducts are the only way to go, which I found out the hard. First I had flexible ducts installed and they off gassed so bad it made my nose burn severely. After several months of this I concluded it would never end and had it taken out and metal put in. What a financial nightmare.
I'm hoping someday (probably after I retire), it will be code to have all ducting within the thermal envelope.
Bypass dampers for zone systems will make it sweat. I never use bypass dampers.
#THEREALHVACMASTER
I couldn't tell if he said Problem Attic or problematic. Both are synonymous lol
I hope you recognize me sir
Time stamps would be good
Time Stamps added!
All due respect if you use a panduit gun on the inner and outer it’s not leaking at all….I realize the codes vary in certain markets but if you use a gun properly there’s no way
I agree
You mean the HVAC guru himself isn't using concrete duct collars? What they heck man, I'm disappointed.
11:21 - A problematic addict in a problem attic (say _that_ three times fast!)
Flex is all garbage, and is even illegal in some areas. Better not put it under a skylight,because it will blow apart from degrading in the sun. I. Have had numerous calls where rats chewed thru the stuff and peed and pooped inside it. Metal duct is the only way to go. But of course, sadly, standards have changed. Flex duct was designed to be used for short connections to the diffusers. A properly used set of panduit straps is superior, but you have to use the tool to tension them properly. They won’t fall off if you use a collar with a bead. Just examine the labor difference. Two straps, liner and outer jacket, then a wrap of insulation over the top. All that fussing over mastic, tape, etc, etc to seal an inferior duct product just doesn’t make sense. I’m not trashing the instructor here, I think he is great. I am trashing flex duct though, I’ll have to admit.
He would get fired his first day at work , you cant do a lot of what he is advising to do !
you obviously get paid by the the word, there is no difference in silver or black , silver is a better product both are based on r value . black would only absorb heat in direct sunlight not from attic radiation. Panduit strap is the standard for flex connection the only superior connection is a steel hose clamp style. you are a shame to professional duct installers .
your already putting in such an inefficient system with a flex monster and duct board trash install it's hilarious to listen to you try to give tips to elevate a trash install to the next level of trash
funniest thing I watched all day, in the real world flex is for the last 5' for hooking to an air device and to help quiet the system
Learn more about radiant heat then get back to me.
Otherwise I hope you have a great day
@@HVACS maybe you should learn your trade before you try to teach others. If by heat you mean radiation then 2 flex ducts laying in the sun the black one would get hot like a black rubber garden hose does and the silver would reflect more heat but we are talking a black attic with no direct light so then black or foil flex experience the same gain from radiation due to delta T and heat moving to cold , ie the cool air in the flex ( radiation) . In this case r value is the determining factor in gain. Open an ashrea book B4 you front on me trick. Maybe you should stop confusing yourself with the properties of infared and should learn your heat.
In general shiny surfaces reflect radiant heat energy. Shiny aluminum foil facing a heat source reflects over 90+% of the radiant heat that strikes it. So a foil like material draped over the trusses will reflect the heat energy back to the roofing materials as long as there is an air space between the two.
lots of wanna be comedians in the class