Not not a long class today, but i wanted to talk about um, just some ductwork stuff, just some just some stuff that maybe you you don't you haven't thought about. Um. Has anyone ever gone in an attic and seen the black you've gone on an addict before? That's good, that's good! That's somebody who develops a problem. They try something because a friend offers it to them.

So have you ever gone an attic and seen that black flexible duct that black flexible duct a couple things? First off? That's different than trailer duct um, trailer! Duct is a specific um. It has a specific jacket on it. That's actually like a water resistant jacket, so it can actually handle um handle water to some degree, uh and so sometimes you'll see guys and i've. I've heard people say this before like oh this, this addict's full of trailer ducts, it's the wrong stuff or i've also seen guys, go and put silver, duct or regular black flex underneath trailers, and so don't get those too confused, they're two different things um, but the Black flex in an attic, what is the uh? What is the benefit and the liability to that duct? Assuming that the insulation rating is the same and generally it is so, r6 has been around for a long time, so there's a benefit and a liability to black flex versus silver flex, and let's see if we can figure out what it is just puzzle on it.

A little bit before i just give you the answer. Any theories matthew. Well, i'm going to celebrate the radiant barrier, so rejection, okay, so that is the benefit to the silver flex. Is that it because it's reflective it doesn't especially from this from the roof deck it rejects, that heat, that's uh, it's being exposed to radiantly, so that means that you're going to have less thermal gains through the walls of the duct, which that means that you're going To have less heat of air inside the duct, especially when the system's off and it's going to pick up less heat.

So what you deliver to the space is going to be cooler. I did a house that had black flex well, we did a service call there and i looked at it with a thermal imaging camera with it off and you would look at the vents and the vents would be significantly warmer than the ceiling temperature and the reason Was because you had this black flex in the attic very hot attic, and it's picking up all that all that additional heat, rather than rejecting it, the way that the silver lining does so that means a lot more heat is entering the space. So what is the? What is the benefit, though, to that go ahead itself lasts longer. It's like the black stuff tends to start melting and getting really right fall apart over time.

Yeah, that's another advantage of the silver is that it does tend to be a little more durable. Now, there's different brands obviously depends on the brand um. There was a type of like grayish flex that we called owl flex. I think that maybe was the brand and that stuff would just fall to bits.

The outer jacket would just fall apart, but there is actually a benefit to the black flecks over the silver. Does anyone know what it is, so the jacket stays warmer right, the outside of the duct, because it picks up more radiant heat from the roof deck. It stays warmer, so what does that make it less likely to do sweat right? So when you take a black flex system and you replace it with the silver flex system, what's more likely to happen because the insulation factor is the same, it's r6 either way. It's more likely that silver flex is going to sweat.

Why? Because the outside jacket of the flex is getting cooler, because it's not picking up all that heat from the attic. So that's a trade-off. It's always a trade-off and always something we need to think about. If you're going to go into an attic, you know again, we talked about radiant barrier, an attic, somebody adds radiant barrier and didn't have radium barrier.

What starts to happen to a lot of ductwork? It starts to sweat. I had somebody uh on the video when i talked about this. They're, like all you got to do, is insulate your ductwork and it won't sweat. It's like okay, okay, guy who's, not from our market of our ductwork, is insulated and uh.

It still sweats in a lot of cases. Now it doesn't sweat all the time. There's some factors. What's another thing that can cause ductwork to sweat that we commonly see that isn't related to an actual issue with the equipment but is related to the way the duct is installed.

Anybody know what's another place, so if you do see a duck sweating i'll ask it. This way, if you do see a duck, sweating where's, the most common place, you'll see it sweat and the where in the pond, what he's a duck a duck in the pond them ducks always making them sweat uh. So what did you guys say at the connection? Right, that's one! What else at the connection, what else your insulation has been pressed where the insulation has been compressed? That is also very true what else? Well, some people won't pull the insulation over the inner bladder. So then it's just exposed where the tab collar is right at the connection.

Okay, yeah, i was elaborating on the connection yeah. Let's talk, let's keep at the connection, so another place that you'll tend to see it. Sweat is where it's touching anything. So when you have a piece of flex duct - and it touches a truss, for example - right where it touches the truss - you lift it up and it's got condensation right there or where it's running over another duct pull that out.

It's got condensation right there and why does it have condensation right there? This isn't a trick question, because it's cooler right there right stuff sweats when it hits what dew point. So it's more likely to hit dew point the cooler it is often we over. We can overthink this. We can get overly science-y for service text.

It's about solving problems right you're, not going in like allow me to take 50 000 measurements and figure out the conditions in this attic like you're, not going to do that. We talk about dew point. So that way you understand when it happens, but how often are we actually going into an attic and measuring dew point and then measuring the temperature of the duct? You know like that's not what you're doing right. What's that it's true right right, you can just do that through your yeah through your sweat.

Those are just some things to watch for another thing that you'll notice sometimes is, if you ever have you ever seen a situation where a duct is running right over the top of an air handler so like maybe it's a supply duct that goes around and loops Around and loops over the top of the air handler, both the duct and the air handler tend to sweat in that situation right, even if they're not touching but they're, just shading one another. So, if you're, if you're, protecting that air handler from the heat of the roof deck, that air handler is going to tend to sweat more, those are all just things to pay attention to, because you can, you know now when you notice it you'll know why it's Happening so when it comes to the installation of ductwork some tips when you're making a connection recognize that's the biggest point that you're going to potentially have sweating. What's the first thing well, first thing is to make sure that it's sealed completely. We've talked about this.

A lot that what is the best way to seal the inner liner to the collar mastic, but what's the trick when you seal an inner liner to a collar with mastic, got to let it dry like you, can't just slap wet mastic on and then immediately pull The outer liner over that's not again, do we do it sometimes still. Sam just gave me this. This look uh yeah, but it's not that's, not the right way. If you're going to do it that way right, if you are going to do it, that way, where you're going to use a liquid mastic, then i would almost prefer you do uh you do that tape, inner liner and i would even prefer that we use more, Like a mastic tape than the tape that we generally use, because it does stick a lot better and then you can go ahead and mastic that that inner liner, but again imagining that a panduit strap is going to keep a duck from leaking.

The panduit strap is just a mechanical connection right and even that i mean that those things can slip off so easy pan to a strap is like just the most basic connection that we can possibly make. Um put some tapcons in it. Uh yeah probably not tap cons um unless it was a concrete collar. You have to make sure that that inner liner gets really well sealed, so tape, squeegee mastic, make sure you mastic the collar in place, so the actual where the collar attaches to the duct board, make sure that's that gets mastic and in a perfect world, if you're Doing a really big duck job you would go through and you would leave the outer jackets pulled back.

You'd mastic, all the inner liners get them completely sealed, let them dry and then go back into the outer. So if you've got a two-day duct job, it's going to take you that long anyway, that's the way to do it, do all your inners have the outers there and then at the end, pull your outers over now. That's not the only reason they sweat. It's not always just duct leakage right duct leakage will make them sweat, that's really important, but but it can also be due to how you pull that outer liner over.

So you see a lot of people they'll bunch up that insulation insulation needs to be full of air. You can't compress insulation, so the idea that you take insulation and you bunch it real tight and you jam it up real tight. That's not really what we're looking for! You do need to roll the edge over for that outer barrier, that radiant vapor barrier on the outside right, and why do you need to have an intact vapor barrier on the outside? Why does it need to be completely intact? Anybody know, because without a vapor barrier, if the vapor barrier is has a gap in it and you just have the insulation, what can make it in this isn't a trick question it's right. In the name vapor, it's not an air barrier, it's a vapor barrier.

We don't want vapor making it in and that's what kind of vapor water vapor. If we keep water vapor out of the inside of the duct, then it's not going to sweat inside the duct. If the outer vape, if the outer vapor barrier is compromised, then what can make it inside that inside the duct vapor water vapor and it can condense inside right. So we have to make sure that we keep hi what's what's happening here from the outside.

It can condense underneath it can get in underneath and condense and correct and between the insulation of the inner liner. Yes, yes, we don't want that no bueno! We got to make sure that that is completely intact. So you take that you take that vapor barrier and you roll it around, but you don't compress all of that. You take it and get it up against the duct board so that it's not wanting to pull back and again that takes having a little bit of slack there get that in there and then, ideally speaking, because what do we typically do with that outer liner? In order to keep it in place, you take a pan to a strap right.

What's the problem with the panduit, strap it compresses it right. So now, what have we done to the r value right there on that edge, where it's already the most likely to sweat? We've done almost nothing to it again. The point is: is that i'm not saying don't do it that way, but a better way to kind of do it is to take tape and actually seal it to that entire area right so that it won't pull off. That is a better way when you see connections that are made that way where that installation is intact, and you don't even use a pan, do it on the outer, because the outer shouldn't really be holding anything anyway right.

The inner is what's keeping it attached appropriately to deflec to the duck board, and i'm just telling you this not because i'm telling you to completely change your procedure for doing flex duct. But i want you to know what causes the problem so, especially in an attic. That's already problematic. We already have sweating issues.

The best way to do it is to do a really good inner seal. Let it dry pull that outer jacket over roll over the vapor barrier and then take tape and tape all the way around now, if you're going to be taping to existing duct board or existing anything, what do you need to do before you start taping? You need to clean it with alcohol. Do not glue it so that part that he just said forget the second part, so spray glue spray glue is in a category of adhesives, called contact, adhesive or contact cement. Okay over time, so it'll do great at making stuff hold for a period of time, but it is not designed to last over the life.

So eventually what happens with that contact cement? Is it dries out? It becomes brittle and then it separates the adhesive. That's in silver tape or in a butyl tape is designed to last much longer, and the key is is that, if you're using glue to make up for cleaning because yeah, you can make anything, stick with a little bit of contact cement. But that's not a good long-term adhesive. It's the same thing is true when we use um uh when we use uh fab tape, that fab tape has an adhesive in it, but obviously that adhesive is not what actually holds the fab tape in place right.

We know that it's there to stick it on temporarily and then what actually holds it in place, the mastic right, the mastic, holds it in place. So, if we're relying on any sort of contact cement to last over a long period of time, then we're kind of kind of missing the boat. You need to have something: that's going to be more permanent and hat taking silver tape. Clean surfaces on both sides.

Nice overlap and a good squeegee, that's going to last forever, but you'll see that you'll see seams on duckboard, that's been around for forever. You go back with people who have done uh connections on air handlers five years later, and you see that you see that plenum starting to detach. We see that all the time right and a lot of times it's because they're relying on glue or they didn't fully clean now again we're always using mastic. Another thing to mention is how many, how many of you here have an outward cinching stapler on your truck matt anybody else.

So really, whenever we're attaching staple flaps - or we call this - the the the ship, lap, flaps or anytime, we're using fab, we should be actually mechanically using an outward cinching stapler to attach everything together. Now again, experience teaches us that if we apply, you know proper pressure, it's cleaned. We do our mastic overlaps, we use fab, it really doesn't come apart, but especially in cases where you're building boxes or things like that that are going to go into an attic using an outward cinching. Stapler is the right way to do that.

If you all know what i'm saying so like when you're, rather than just relying on the adhesive for the um for the fab tape, you're actually putting the fab over that that overlap and then you're stapling it in place. And now it's really gon na really gon na hold, and this might be new to some of you um, but that you know again there's a lot of things that we get away with uh that you know really aren't the best way. So again, when we're installing ductwork keep in mind what type of ductwork it is pay attention to that pay attention to the material. If it's black, it's going to be less likely to sweat, but it is going to be less efficient right.

We want to make sure that when we're strapping ductwork we're suspending it in the air, we don't want it touching other ducks. We don't want it touching trusses, because a lot of old-timers will be like what's wrong with just string it along the trusses. The truss is the strap right, but everywhere it hangs and sags over that truss everywhere it compresses that insulation is going to be likely to sweat. A strap properly suspended is not going to be nearly as likely to to sweat, even though it might be a little compressed, because it's not up against anything there's an air gap around it right so properly, strap and then, finally, when you are doing duct work, make Sure that you're pulling it tight ductwork should never be this wobbly snake through the attic.

In fact, the right way of doing ductwork flex duct is to only do straight runs of flex. If you use straight runs of flex and you pull it tight, it functions pretty much just like metal it's when we go like oh i'm going to go over here and then i'm going to wrap around there and then i'm going to do all this. Ideally, you would go straight and then, if you had to make an angle, you would actually put a fitting in place a metal fitting you'd attach the flex to the metal fitting you'd make the new direction. Then you'd go straight down to your box and again, if we're towing it to the top of a box.

The way we generally do then you'd have a metal fitting that would go down into the top of the box, so you wouldn't make that last bend and that reduces a lot of insulation compression which reduces um sweating, and it also makes the duct perform a lot Better, you have a lot less turbulence and a lot less friction now again. I know that you're not going to do that in most the cases of what we do, but just knowing that will make you run your flex differently. The best way to think of it is imagine the air, through your duct and jim berman talks about it. This way, imagine the air, through your duct, like race, cars and you're, trying to make it as easy as possible for these cars to race around this track.

The more bends that you give, the more likely these cars are going to hit in the corners and spin out, because that's literally what the air does anytime, we turn it in the inside and outside corners. It hits and then it creates this turbulence and that creates significant resistance inside the ductwork over the length, thanks for watching our video, if you enjoyed it and got something out of it, if you wouldn't mind hitting the thumbs up button to like the video subscribe to The channel and click the notifications bell to be notified when new videos come out. Hvac school is far more than a youtube channel. You can find out more by going to hvacrschool.com, which is our website and hub for all of our content, including tech tips, videos, podcasts and so much more.

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