Hey thanks for watching this video. This is one class from the 2022 hvacr symposium in claremont florida. We have the symposium every year and so to find out more information, kind of upcoming go to hvacrschool.com symposium big thanks to our sponsors. For this event, which was accutools and truetech tools, they're the two title sponsors that made the event possible.

This session is with our good friend and long-time contributor eric kaiser, where he talks about the envelope of the home or the structure, shell of the home, being the biggest duct that you run into all right. I got the thumbs up. Everybody we're ready to start who all we got in here that i can pick on today. Let's see i got russ king back.

Oh, we can pick on this guy trent, trent davis, i'm picking on you, that's what you get for sitting in the front row right, fair enough. We can do that all right. So thanks everybody for coming in my name is eric kaiser and today we're going to be talking about the question: is the house really a duck system? Okay? Is it a duck system? This is a question that goes around the industry. I've heard it for a long time and excuse me i'm going to walk around and talk with my hands a lot.

So if i get to waving and pointing and all kinds of neat stuff, that's just the way i work um and this kind of bugged me for quite a while. Is it really a duct system? Should we treat it like a duct system, or should we not treat it like a duct system, so i got to thinking about it. I looked at it and i'm going to leave it up to you for right now, but at the end i'm going to ask some questions of you guys, and i want you guys to answer me and tell me what you think after we go through this and Then i'll tell you what i think: okay, now questions if you've got questions shoot a hand up in the middle of it. Let's ask them we're going to talk about several different things here, as it says, and some other semi-related stuff, so we'll talk about several different things in here.

Um, don't be afraid to ask the questions with that. Did anybody get that spaceballs to disclaim okay? All right all right, so, okay, all right, so the lawyers really love this one. Okay, all right! So all these exp opinions in here their mind, they're my experiences or experiences. Maybe of other people around me.

You guys use them. Misapply them apply them at your own peril, or success. Okay and everything's subject to change something. I've learned over my career doing careers doing various different things always be willing to change.

If you are not willing to look at something else, when somebody presents you with good information, you're stuck and you're going to be stuck right, where you're at that's something, i've learned i've been there. I've been stuck i've thought about things and i've learned to change. So if i get new information beyond what i'm presenting today, my views may very well change on this down the road. You don't know, okay, but be willing to change all right.

So what is a house? And we really need to ask that question a house. This is from wikipedia is a single unit, residential building, various levels of complexity. It can be multi-levels, it can be one or two rooms. Like my parents house, when it started out, it was four rooms, a bedroom, a bathroom, a living room and a kitchen, slash dining room.

That was it well. It got a lot bigger over the years. We use multiple materials, all right and outfitted, with plumbing electrical heating, ventilation and air conditioning systems all right, so there's a clue. Maybe now what is a duct system that that's not a duct system? That's just a bunch of ducts.

All right again, i went to wikipedia because i really like the descriptions they had in there ducks they're conduits they're passages. They connect things, heating, ventilating air conditioning a lot of times. Those are very intermixed, but sometimes they're, not something that's often forgotten about in our industry. Is ventilation and if we don't pay attention to the v in hvac you're, an hac in my opinion, say that i see a lot of hvac contractors ignore the v.

Oh, that's a plumber that can put in a bath fan guess what guys bath fans are. Our! That's our job. Okay. Does a dryer ventilate your house? It's our job, that's ventilation! That's ducting! We should be taking care of that.

We should be working with the homeowner. We should be talking to them about that right. So ducks also deliver ventilation, air and they take care of exhaust air. So there's more information for you now, let's do a little compare and contrast houses versus ducks house versus duct houses.

People live in them right. We expect to be comfortable. We expect to have that comfort within our house that we desire versus ducks animals and toys live in those. If you haven't found an animal in a duck, threat or or evidence thereof, you may not have been in hvac for a little while at least not some of the places i've been.

I've found toys, i've found construction materials evidence never found a live one. Yet i found a cat had a cat crawl in one once while i had the uh furnace out and almost didn't get back out, because he went too far in the duct, and i almost didn't find that, let's see what else have i found raccoons things like That so in a house, we really want to have lower air velocity typically than in our ducks. So ducks have a higher air velocity because we're delivering something from point a to point b and we're going to bring up another point with that as well. But when we get into a house we're talking about human comfort and we need to be very intentionally careful about the velocity and where we put it, because if we think about air and we're talking, obviously about a lot of forced air systems here, because that is The most common or the most prevalent conditioning system in our houses in in the us when that error comes out of a register.

What does its job become? Let's go a little further than that and i like, where you're going, but let's go a little farther than that. What is its job in the house specifically to do what's it? What is it going to condition to make the occupant comfortable? How do we make occupants comfortable we're going to remove or add heat? So if we bring air what i call over conditioned air because we don't want to live in the house at the conditions coming out of those registers right? If, if we're trying to heat a house up and we're blowing, say 110 degree air into that house out of a register, we probably don't want to live in that temperature, so we're over conditioning the air in order to condition the house 60 percent, roughly of human Comfort is comes from radiant heat from all the surfaces around us, which means that the job of the air coming into the house is primarily to control the surface temperatures of what's around us. Where does the primary heat transfer from houses come in? What's that surfaces windows is one place, walls exterior surfaces, exterior walls is the primary or roofs or if you have a house with a free-flowing underpinning under it, you know if the air can move underneath it. It may be your floor.

That's where the majority of the heat transfer in the house is going to happen. We also have things like infiltration that we have to deal with, so we need to control humidity things like that, but we need to control the surface temperatures if i, if it was 10 degrees outside and i'm standing next to this door right here. Do you think? I'm going to be comfortable, not really. I can lay my hand on that door right now and i can feel it's warm the sun's hitting it.

It's going to make it hot in here, especially to people sitting right here in front of that door, because we have a path, so the air really needs it comes in over conditioned and its job is to condition most of the surfaces and some of the air. In the space, so does it do good to blow that air out into the middle of the room, or would it be a good idea to follow the surfaces inside the room and maybe condition those surfaces but not blow the air on the people? You know if you, if you want air blowing on you, turn on a fan unless you have a customer that really desires that air blowing on you. I don't like to close doors completely folks. I've heard of a couple situations where people wanted air blowing on them.

They sign off on hey i'll design it that way, no problem, it's your house, not mine, i don't have to live in it. That's your house, but we've got to have that velocity. Now our heat transfer in our house is minimized. Okay, we want to minimize that with insulation, air sealing, etc, etc.

In ducts, our heat transfer can vary, but realistically we in a perfect world, we have zero heat transfer in and out of our ducts before it gets to that register, the less heat transfer we have in the ducts, the better off that air is going to be To condition the space right, which is where we're our goal is to condition the space where people live, because the ultimate goal is to keep people comfortable, and we want to keep them as as comfortable as they desire and as inexpensively as possible or as they're willing To pay for got some differences. There house has fenestrations windows, doors, stuff, that's cut in the walls. Okay, duct really shouldn't have any fenestrations on it right that should be nice and sealed up and tight, because we want to deliver that air from the equipment to the house without losing anything. We don't want to blow air out of our ducts or pull air into our ducts unless we can control it, so we seal them up tight.

Hopefully, houses have kind of what i call fluid operation, people open and close doors right people move furniture around in their houses. You ever had somebody set furniture on top of a register ever had people. Somebody set it on top of a return, grill yeah. It happens.

Well that changes things so make sure when you're designing stuff that you start to think about hey. Let's put those registers in places where people can't do that because a lot of times the last thing somebody wants to do is think about. Oh, i can't put my couch on this wall because there's a register there, how many homeowners have you ever talked to that thought about that russ king is going to solve that idea. Someday he's got an idea if you guys don't know russ king back in the back, he's the uh creator, one of the creators he and his son are the creators of the quick model load, soft load, calc program, mint baby mint.

I love that program. Okay, so ducks they also kind of have some fluid operation to a certain extent, because i count registers in ducks and people can close registers when they don't like them or if they want to not condition a room or they think they don't want to condition a Room, they also may have dampers in them. If you have a zoning system, they should have balancing dampers in it so that we can control the air flow from place to place if we need to okay. So those are all things that should be in ducts.

The house can it affect the airflow going to the equipment, because we need to have a certain volume of air going across our equipment to make the equipment work properly. If somebody closes a door in a house, should it affect the airflow at the equipment? Can it affect the airflow at the equipment? There's two different questions there should it and can it it does it can affect the airflow? The ducts also affect the airflow to the equipment, which is why we have to size our ducts properly, because if we don't size our ducts properly, our equipment doesn't get the right airflow. It can't do what it's supposed to do. What we designed it to house doesn't really control the air direction when it comes out of those registers.

The duct system does, though, the duct system has to tell that airflow where to go right to condition the surfaces in the house condition. The air in the house get that house to comfort, house and duct should both be tightly sealed now, which one is easier to seal the ducks houses are challenging to seal up, especially if they're already existing new houses, it's easier to seal them up, but there's still A lot more work to do in that than in aries ducks, because guess what ducks are a lot smaller and they quack? If you squeeze them? Oh, yes, there may be intentional unsealing of ducks again. It depends on the situation um. I like to have my ducks perfect as close to perfect as possible, because i prefer to have control over where the air is going.

I hear that i'm purposely leaving my crawl space. That's up to you. Those are your calls. That's your crawl space and you got to live.

There works fine at my house. Heat works great at my house. Air conditioning works great at my house. You know, that's that's that's where i have to come to because the customers pay the ultimate price, you you know.

You're living there, i'm not so it's it's got to be your decision. We kind of talked about this unintentional volume control. The house has unintentional volume control into spaces in the house versus the duct. We have intentional volume control with balancing dampers things like that.

Where we're setting up a system or commissioning that system, but the house may have unintentional control if we don't design this, if we don't design the duct system intentionally, what we need to do as designers is make sure that the house doesn't affect the air flow going Into the space, if we want to maintain comfort in there, we don't want that house like a door closing or something like that to adversely affect our airflow volume, because airflow the airflow volume, not only the volume, but we're also going to talk about airflow patterns. Okay, both of those play into whether or not we can keep a house comfortable, because i'm going to show you that here in a little bit in in one of these slides, so any questions so far you guys are all kind of going to sleep. Am i that boring, no, no, all right so stuff that happens in a house. Let's take a look at that kind of a normal layout of a house right.

We got a, maybe a living room here, kitchen mechanical room, maybe with a laundry in it. How often does that happen? You got furnace washer dryer, let's see what else all the cleaning supplies the vacuum: cleaner, 92 brooms and dust pans, and what else gets stuffed in that closet, water, heater? Okay, that's all going to be in there and we got a bathroom over here. Closet mask this is going to be our master suite here we got you know bathroom or a bedroom and another bathroom over here. A couple other bedrooms all right.

Let's take a look at a few things: let's look at that house from the side. We got a pressure envelope all the way around that house. Now our fenestrations our windows doors things like that they're going to penetrate that pressure envelope, but they really don't change the pressure on the house, even though they make a penetration they're, not intentionally changing the pressure. They don't have the power to do that unless the wind blows, but if i put duct work on there and say that duct work is outside now i've made an intentional penetration into that pressure.

Envelope of the house with my duct. So now we've expanded that pressure envelope. You guys ever worked. Anybody ever worked on a house that looks similar to that lots of them right.

What kind of insulation is required at this point right here right up here in this attic top of my how much okay? Why do we run high velocity higher velocity in these ducts because time plus temperature equals heat transfer? So if we take it past faster, we don't get the heat transfer all right. So we got to watch that now it's not a terrible problem in ducks uh. What is it? Is it manual d that says really low velocity is the last thing you should be worried about in ducks, i'm paraphrasing that a little bit from memory because, well you know my memory's got a lot in it things stink, but again with down here. We penetrated because this had this happens to have a sealed crawl space on it.

If you saw the vents on both sides, this happens to penetrate in multiple places, our pressure boundary, because we need to have that pressure boundary on the house. Now you can redefine those pressure boundaries and i work with a lot of existing houses as opposed to new houses. You may have to redefine pressure boundaries for comfort, sometimes, but that gets into a little bit more of what we're doing here now. If we kick that fan on, we create a pressure differential here right, we're at negative 0.2 inches of water column in that duct positive 0.12.

Those ducts can intentionally they create pressure differentials in them, because we have to have a pressure differential to get air to move. We don't have differential, we don't have air movement, so we have to think about and again this goes back to air sealing if these ducts are leaking say if i'm leaking um, we'll save 50 cfm out of my supply, duct down here, where's that air going to Come from i'm going to blow 50s take 50 cfm out of the house, we'll pretend there's no leakage in this duct. I got a supply. Duct 50 cfm goes into my crawl space, which leaves the house.

Where does that air come from? I heard everywhere that it comes from what comes from. Does the house make air? No here's! The rule one cfm out equals one cfm 50 cfm out equals 50 cfm in those slides. If we go back here, do you see anywhere where external air is going to come back into the house in a controlled manner? They got backdraft dampers in them, probably okay, they should have backdraft. Dampers should have tight ceiling, backdraft dampers in them.

Air takes the paths of least resistance. If you find one, don't assume it's the only one, because it's going to go wherever it can, because if i'm blowing 50 cfm out down here, i have to put the air back into this house somewhere the house collapses. Anybody ever crawled up in an attic and seen dirty insulation, black insulation. You need to change that.

That's the whole house, air filter, it's dirty! It needs to be changed. How often do you change the other air filters on your system? Change it when it gets dirty? It's past due it's dirty, but realistically that's what insulation becomes if we as ventilation contractors do not control the ventilation air coming into the house we'll get to that in a little bit all right. So let's take a look at this house. When we talk about house measurements and i'm going to go into some pressure measurements, some differential pressure measurements here a little bit now, when you're, taking these kind of pressure measurements on a house.

If you're an hvac contractor, how many of you carry a manometer in your tool bag or on your truck, that's it. I think a few more of you need to go, buy some tools all right when we start talking about pressure measurements on a house, how many of you carry a manometer that can read down to a pascal or even intensive pascals, a couple of you digital? How what what scale do you normally read on in a manometer two and a half pascals is 1 100 of an inch of water column, so we're talking about a very different pressure scale here all right. This is a much smaller pressure, scale, uh and the reason being that we're talking about in a house we're talking about a huge surface area when you think about the entire shell of that house and even a small pressure differential which you're going to see here in A little bit can create massive problems, so we need to be intentional when you choose a tool to do this, find a manometer that can measure in that one pascal range, my personal favorite out here is uh tec's got a dg, their dg8 manometer. It's a fantastic little tool.

It's you know it's it's a little more expensive than the ones we normally carry for setting gas pressure and things like that. But anyway, if, if you're talking about a good manometer that one they also, if you want to get into two-channel stuff, to do more, testing, they've got a dg-1000 and retro tech also has a their dm32 is also a good gauge to to measure those with so Yeah it's and what is an atmosphere right, yeah yeah, it's a small! It's a small amount of pressure, not it's not not as small as microns, but it's much more fun. It's much finer than inches of water column when we're talking about ten nat farts. Okay! So is that is that the official measurement david a pascal is a a micron.

Is one nat fart and a pascal is ten nat farts. So when we talk about house pressures, okay, we utilize the pressure outside the structure as our zero reference. That's our zero point and we measure up and down from there to look at differential because again, if we have differential, we know that we have air flow right, there's a potential for airflow there. So, of course, if you have differential across a perfectly sealed surface, you're not going to have air flow you're just going to have differential, but how many houses do you know of that? Are perfectly sealed, they're perfectly airtight never going to leak a a nat fart of air? They don't exist.

Some of you all duck systems are getting pretty close. Where's doug at doug in here doug's got doug and neal, i think, are the are leading right now in the duck: tightness testing all right, you'll notice. These are these are nil, compareto ducks and these are flex ducts. Everybody else puts in.

So, let's kick our blower on again. We kick that blower on. We see that .12 in our supply 0.2 in our return. Well, that's a little high because we got a filter grill out here.

If you notice that in the drawing of the house, we got a filter grill, so we should expect a little higher in our return static, because that filter is away from the unit. But the important piece here is we're only circulating air in the house: zero pascal's, a pressure differential - and this is called measuring in the house with reference to outside. It's often shortened up to wrt with reference to, and that tells you where you're measuring reference to when you take static pressure on a unit or you set gas pressure on a unit you're, always measuring with reference to the house. Okay, you're not measuring with reference to anywhere else, because your other port is typically open on your manometer or if you have a single port manometer, it has an internal pressure reference to that house.

Now, i'm going to say one thing for the higher end manometers out here: how many of you turn your manometers on and take a test and then remove the tube and you look down at the screen and it doesn't go back to zero. How? How far does that drift two to four inches or or point two to point four? Okay, so we're talking two to four tenths, that's still a pretty big drift. When we're talking about that, i mean i've seen up to an inch of drift. It especially happens when we change temperature spaces with our tools uh, so if we're coming out of a cold or a hot truck going into a colder, warm or warmer house that causes drift in electronics.

Now, when i go back to mention in those three gauges that i did that are sitting out here, that you guys can go pick up and play with those are what's called auto zeroing. So when you turn them on and you're listening to them every once in a while you'll hear that click click inside to one of those meters. That means that that meter is auto zeroing itself constantly. So it constantly keeps a solid, zero reference.

In other words, it doesn't drift. Yeah you're gon na pay a little bit more for that feature, but man is it worth it to not have to go back and repeat tests over and over again. I wish i had had that years ago, so some cool stuff there. Now, let's take a look at something in this house and we've kind of talked a couple.

We touched on this a little bit. Anybody notice that door closed central return, tight door. What do you think is going to happen to this room? Okay, you think customer may have a customer uh complaint on that room. Why do you, what kind of complaint do you think they might have cold or hot we're gon na say this is in the heating season? Okay, since it's winter in florida.

Right now i mean where i'm from it's winter. This is like i'm wearing short sleeves and the door's getting hot, but so what kind of complaint do you think they might have in the winter time in that room? If that door closes and it's fairly tight, it gets cold in there. What would you do if that room got hot instead of cold air flow? Doesn't noticeably change less than 10 percent differential, measured before and after the door closed infiltration? Well, if we close that door what's going to happen to the pressure in that room, let's take a look here: okay, complaint over conditioning and russ i'd like to thank you very much for making me think about this and do some testing on it. Over conditioning i've had this problem happen from my customers right, a room gets too hot in the wintertime i'm like.

How does that work? Well, too much airflow. All right. I got 4.2 pascals now. How many inches of water column is that less than two one hundredths of an inch of water column? What's the accuracy on your uh typical gauges that measure water column, it ain't great! I promise you it ain't great.

Okay, high accuracy gauges get us high accuracy, measurements which gives us the better chance to make high accuracy decisions and make high accuracy recommendations to our customers. So i got 4.2 pascals of pressure here room with reference to the rest of the house. My house goes 0.6 negative, which means the the rest of this house is at a lower pressure than outside. What's that mean i got air coming in now, it's pressure.

Differential air is going to try to come into that house and it is. It has to be because otherwise the pressure would just keep going down and down and down until the house sucked in and imploded i've never seen a house implode. Yet can't say it's not going to happen. I haven't seen it yet.

So we got air coming in to the house everywhere else. We got air coming out here, but we got air going out here as well. We know that because that happened, if all the air was coming back into the house, we may have a pressure differential here, but we wouldn't have that over there. So we know we got air going out how much air we don't know, but i know i got 3.3 pascals of pressure difference here: lower pressure, lower differential, so i'm looking at 4.2 a differential here 3.3 there.

Where is most of my air going out of that room? What do you think what direction is most of my air headed volume, wise exit where to the outside or back into the house right? So it's taking two paths. It's part part of it's going back into the house, but the majority of it's going to be going outside because my pressure drop is lower there. Now. Why did that room over condition? So there's no return on the door closed.

If i blow air into this room and the door is open, what does that air do? What? How much time does that air spend in the room, and i like to think of this as laps around the room? How many laps around the room is that air gon na make if that door is wide open, so it's gon na come into the room and it might make one complete lap around that room before it leaves and goes out here now. We should have that thermostat set somewhere close to here, because we want that close to the return, because what is happening as the air makes its path from here to here and through all this is it's shedding heat onto the surfaces. So when we get back here, if this is set at 70, we're probably hopefully going to see maybe 7273 degree air coming back to this point, because we're never going to get back down straight to that 70 degrees, and it depends on what the surface temperatures are. Now, if those surface temperatures are say, 50 degrees, oh, i can definitely have 70 degree air coming back here.

I could have lower than 70 coming back there if those surface temperatures are that low, because i'll drop the temperature of that air even farther, because, of course, when heat moves, we have to have a differential, but what's happening now in this room that doors close, i Lost my my low resistance path back to the return, so i lose my low resistance path now that air mate might make a couple of laps in that room before it leaves, and it finds all the little holes all around that room. Well, if it's going to stay in that room, maybe twice as long now, it's got better dwell time because, realistically, if you look at this, like i said 4.2 pascals - that's maybe .015 inches of water column. How much is that going to reduce air flow in a duct .015 inches of water column? That is not a significant increase in my duct pressure. It's not going to change it much! Maybe 10 percent not a lot of not a lot of back pressure there.

It's spending more time in this room because dwell time tells us how much heat we can transfer. So i get an over conditioned room. The rest of the house, of course, is now getting unconditioned air brought into it, because it's coming in through the walls and i'm not having this much come back here to my return. So the rest of the house slowly comes up together and waits for the thermostat to satisfy, while that one room is getting a little lower volume of air.

But it's spending more time in the room. So it's got more time to shed its heat into the room, which makes it over conditioned or hotter. It can yeah, because what that can do. Register selection is highly important because we want to blow it on the surfaces.

If i just put this register in here ceiling floor whatever and just blow it straight, what's it going to do it's going to go straight up, but think of that, as i'm think of this as the register right here i blow straight up, and maybe i spread Out how much of that wall am, i missing might be missing a significant portion of that wall register selection and register placement is exceptionally important to getting quality comfort in a house, because realistically we want to blow that air across all those surfaces in that room. If you had jonah walk's done some good stuff on register placement, of course um is it manual t you've got you got to use manual t to do that? There's some other new products and a new, a new duct system out on the market that i've seen that i'm really curious to try and i think i'm actually going to apply it in part over all of my house that uses smaller ducts, not high velocity standard. You put up standard equipment and you just put more of them in there, so it fits inside regular walls. It's super simple, yeah yeah it like a pipe or, and they advertise it as like.

14 skus makes up their entire duct system and i'm like yeah. It's called rhea, i think rhea i got ta. I got ta look into it. I actually know a guy that works there.

So for you on this tool, great question, i don't know i haven't tested one like this with a good show yet to find out. I don't have data, so my assumption. My ex my assumption would be that if you get this room as equally as tight as your duct system, well then it's going to have to force it all into the house, but the chan, the challenge there is, if that's equally as tight in your duct system. You're going to create a ton more back pressure and you're, going to lower your airflow, which then you get the cold room, uh depressurization right! It's a house under pressure, depressurization of a house means it's a house under pressure, because the inside of the house is now at a lower pressure than the surrounding environment.

So it is a house under pressure. Quite literally now we get depressurization from things like bath. Bins range hoods, anything that takes air out of that space, which means that air has to be replaced somewhere. Do you think your customers want to have conditioned air coming into their house, or would they rather have random unconditioned air entering their houses, which one's better for them now they're going to have to pay for that? You should absolutely offer it to them.

You should figure out strategies that work for your marketplace, because there's way too many markets out there for me to tell you what to do exactly unless i know more about your marketplace, but you need to figure that out. We can also get it from non-direct vent appliances like water heaters, furnaces and fireplaces. They all depressurize. A water heater is a great example of an almost continuous depressurization, because if you have stack effect going out that at any point in time, doesn't necessarily mean there needs to be steam coming out the top.

But you can have stack effect heading out that all the time so be careful with those and know how to test them for it. Now, let's try to jump through a couple things here so depressurization. We turn this exhaust fan over here. Maybe i depressurize that house five pascals, two one hundredths of an inch of water column, again really small numbers here.

When that happens, we have to have makeup air if you're familiar with that term from commercial or restaurant type things all right. Makeup. Air counteracts exhaust air in a perfect world. We want it to be equal.

We want to keep that house pressure neutral as much as possible. It's a great idea to filter that, because outside air has who knows what, in it i'll show you my favorite strategy here in a minute, uh should be filtered dedicated. Dehumidification can be a really good idea in green grass or humid climates, and that is because you need to really control that humidity coming into the house in a lot of cases. Okay, now, if i have a house like this and a system like this where's, a good place for me to bring in fresh air or make up air, i need to bring make up air into that house to counteract those.

My favorite place is the soffit. If i can or the roof, i don't like doing roofs in my environment because i get snow load on roofs and that covers up vents and we still need to have that ventilation indianapolis. So i would do a soffit over here now. You've got to be intentional about where you're putting this to make sure you're not going to get other stuff up in that.

But i want to bring it in through another filter. High merv filter right here, oversized duct ever loving dog crap out of that filter make it big low pressure drop watch this. If i got negative 0.2 inches of water column pressure coming in here, i got a good pressure differential to get plenty of air back into that right. What can i put in this duct? If i get too much air dampers, i can control it.

I can measure the airflow and i can say i got too much air coming in. I don't need that much. I'm gon na turn it down perfect man. What happens if i don't oversize this, i make it real small.

I put a little teeny tiny filter in there and i don't get enough air in there. Well, then, i got to tear it all back out and start over again and my customers pissed, because i didn't do it right the first time. You know it doesn't cost that much more to upsize the filter. I do a 20 by 20 filter on that thing.

Do a high merv filter on it, make it right now balanced ventilation. This is a lot of times called ervs or hrvs. You have equal volumes. Coming in or out that can be really useful if you have a space with a lot of vocs things like that, where you need continuous ventilation to mitigate something, that's in that house, but you have to be careful.

You have to be intentional they're not intended for makeup air because they create an equal or balanced flow in and out constantly, so don't rely on those for makeup air. Those are only for ventilation. They also have limited control of humidity in high or low temperature times. They can do okay, but if you have really low differential, you can actually with low run time on your equipment.

You can cause high humidity in houses with an hrv or an erv, so be careful of that. There are versions like the serve 2 out there. That use refrigerant to transfer the heat between the air streams, as opposed to just using a a passive core, and if you want to know more about that, look up the building science podcast with bill spone and um building hvac science with bill spone, i think, is The title of the podcast and he's got a bunch of information because he applied one in his own house, so he knows quite a bit about it now. Do you guys consider the house a duck system, or do you consider the house a connector of multiple duck systems all right and should a house be treated like a duck system in some instances or in every instance now here i'm real fast? Can i have two minutes? Okay, i'm gon na go through a quick, my design considerations.

When i'm looking at things, don't pressurize your rooms, you want a low resistance path. I'm going to try to get done here, so the next crew can come up and get this central returns. Do that with rooms with low airflow per room. Typically, all right, ducted returns on rooms with high air flow per room or higher airflow per area use the appropriate friction rate when your returns are ducted, because you want that's going to bring that low pressure from the fan into that room.

But you need to make sure you've got a low resistance path back to the filtration or back to the duct system. If you can start calculating the pressure drop of a house based return path, if you look up some of the stuff that mr general garcia has done, he has found some crazy, high resistance on louvered doors. So if you work in a market that requires that utilizes reliever doors watch them they had is jenny in here. I don't know if he's in here right now he's how much what's your highest door to date - generally 0.24 inches of water column across a louvered door.

You ever measured that not of air is flowing across it and it's a high resistance path. You got to think about the free area, all right don't blow air on humans, unless, of course they want it. 50 to 100 is going to be pleasant. Less than 50 is typically going to go unnoticed blow air across and at surfaces, especially those that conduct heat all right.

Those are the ones coanda effect. If you haven't heard of it, look it up. It adds about 25 percent, roughly to your throw distance on your registers. Control your mean radiant temperature.

Oh, this is a neat one i found out. Did you know room color can affect up to seven degrees of perceived temperature. Why do you think they call them warm and cool colors? I didn't know that that was kind of cool control. Your stratification, of course, which is your vertical temperature gradient by air mixing um, and by doing that, that's our continuous fan run time is going to help to to eliminate that stratification.

And, of course, if your equipment is running and sized properly, that helps greater temperature difference equals faster heat transfer, balance your makeup air to your most used exhaust, because a lot of times, if you put have to put a makeup air fan in you're, not going to Be able to vary the speed of that. You may have three or four different exhaust fans in your house, balance it to the most often used. One is my general rule, and but you need to pay attention to kitchen exhaust, because there are a lot of kitchen exhausts out there in high-end houses today that are stupid, high cfm stupid in my opinion, are you finding dryers off in the highest yeah? So you might want to balance to the dryer again. I count that as an exhaust fan but consider that dryer.

What do you see in volumes? Chris wow? Okay, that's a lot! So look at your dryers yeah because it's a high velocity system right, i'm a big fan of interlocking my exhaust and my makeup air. I want to make sure that anytime, an exhaust fan kicks on. I can get makeup. Air turned in turned on whether it's a damper, whether it's a fan whatever it is.

I want to make sure that it's coming back in neutral house pressure, aim for that filter, your incoming air separately. Now we don't have a lot of time so i'll be outside or in the back if you've got other questions. Thank you all for coming. That's my email! If you need to contact me for any questions, thanks for watching this video again to find out everything we have going on, you can download the free hvac school app on android or on iphone or go to hvacrschool.com and then specifically up in the top you'll.

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