I'm just doing a little bit of practical training on manometers. We use manometers in air conditioning to measure what okay and gas pressure. gas pressure. Which maybe not air conditioning.

That'd be like a furnace and gas pressure in pool heaters. So we're going to talk today about static pressure and what that is. We'll just start out by somebody tell me what is static pressure on a system when we're talking about airflow. Static pressure, Turbulence? Okay, pressure.

Okay, so oh yeah. an outward pressure? That's good. Okay, so what creates that pressure in the inner system? It's a blower. Yeah, airflow is more precise.

Airflow creates the pressure, right? Okay, so our static pressure is this. We have our blower that is pulling in air and pushing it out right? So your static pressure is as the air comes out. the resistance to that airflow is your static pressure. It builds up pressure inside of whatever compartment it's in the duct work And there's resistance.

So in the picture I have right here, we have almost no resistance to our airflow. Right in this side, we have a little bit of resistance to our airflow and the picture. I've drawn, what is it, filter and the coil. Okay, so then we have our our blower pulling in air and then pushing it out.

So we have two different types of static pressure that we'll be measuring which are positive and negative. Positive and negative exactly. So let's think let's just start with positive. It's the most intuitive.

So if this is my ductwork, we turn the unit on. The airflow is going to flow into here. it's going to hit a dead end. and that pressure that is pushing against all the different surfaces.

That's our static pressure. And so it's the resistance to the airflow. So we take our probe in there and we're measuring how much pressure is pushing against what is resisting the flow of the air right. And then, uh, what we end up doing is attaching some ductwork to this system.

And do we have, do we still have a static pressure resisting our flow? Yes, we do. Especially on that one. Yeah. So, but we've released a lot of our static pressure, right? and this will go to the other side of the house, much larger duct into the Attic And now we've released even more of our static pressure.

So he's never put ducks on the end of the bottom like that. That's it. This is Not how this is done. When you are measuring your supply static pressure.

You're measuring what past this point, wherever you're measuring is causing resistance to airflow and how much resistance is that? So your manometer is going to read inches in water column, if you pull up your phone you can actually see that and then in on your return side. We have negative pressure, right? So we have our blower in here and it's pulling in. So your static is the same in that it's how much resistance do we have to that airflow. But it's not a resistance, it's pushing against the surface.

It's pulling so your air as you turn this on is pulling on the panel. You feel that when you go to a panel while the blower is running, it's pulling on the coil. It's pulling on the filter. It's pulling on the sides of the duct work all the way to our return Grille face where we heal the whistling as the air pulls on that return Grille or catches the filter in there, so that makes sense.

So then as we're measuring our static pressure, we're looking for external system total external static. This is a measurement that is done to find out how well is my unit operating, how much airflow do I actually have? how much resistance is the blower fighting? So our external static pressure is taken above the filter right here and then on the outlet before the rest of the duct work. And so this is measuring just our system as it would come from the manufacturer. So that's what your external static pressure is and so you'll see external static pressure listed on your data tag.

It'll tell you what the manufacturer used to test and get all of their performance data and then you'll see external static pressure used when you're looking for setting blower speeds and you need to to know where to make blower speed adjustments which I'll just talk about briefly in a second. but I did want to point out is some of the differences in like counter-intuitive stuff that can happen if you're not understanding static pressure and how it works. So let's say that we have a Merv 8 and let's switch that up to like a Merv 13. Okay, so if we have a Merv 13 here, how is that going to change my static pressure reading if I put it into the return right here, put it behind it.

Yeah, so I'll have a lower static pressure, right? Why is that behind the filter? So you're behind an area of high resistance. So if we were going to actually see how much the filter is affecting the systems static pressure, we would put it on this side of our filter in the area where you actually have the most resistance you know, after your airflow restriction, right? So it it's a a common mistake that guys make that they will just test on the return and they'll see that they have a low static and they assume that that means they got good airflow going through their return. Whereas if you have a clogged filter or a restricted coil, your blower may be under severely High static and you don't know it because you're testing behind the point of the restriction. So let's let's just think about it this way.

if we have a restriction in our coil or blower, what ends up happening is that we eliminate a lot of our airflow. Before that point, you still have the air trying to pull through here, but you can't move as much air right? So we're eliminating a lot of our airflow. That means there's less of a vacuum to pull on all sides right here after the the before the resistance. but on this side there is a much stronger vacuum being pulled.

so you have a higher you'll end up having a higher static pressure. If You measure in the right place. Does that make sense? Okay, did you just pull out the filter and still measure further away? Will that affect the measurement? Yes, you can. So if you're looking for how has my system actually operating without the filter, you can pull it out and measure here and you'll have.

You're not going to be able to measure what your coil, how much your coil is affecting it, but your filter. You can pull it out and compare and that's often what you're using a manometer for. You're you're doing before and after analysis on like a filter or a situation, trying to figure out how how have my what I just changed affect the systems operation right? Okay, so if we have a clog filter and we have less airflow being pulled in, how's that going to affect my Supply static pressure, it will be lower. Yes, you guys are both right.

Yep, we have less airflow that can actually be pulled into the system because of the Restriction we have less airflow than coming into our ductwork. Which means there's going to be less external pressure on our system. So if you take your probes and you measure here and you hear and you have a restricted filter or coil, you're actually going to have a nice really low static pressure reading. There's not going to be a lot of airflow here.

There's not going to be a lot of airflow here because of the restriction, so there's not going to be much pressure negative or positive in your ductwork. and you'll get a false low in that you're looking at your numbers and you're like, okay, I have 0.2 That's great. There's not much resistance for my system, it's not working too hard. I Must have the airflow that I need when in reality you're just measuring at the wrong place, right? So when you measure systems, external static always go above your filter and above the blower in the supply.

That's important Also, for Diagnostic. Let's say that our coil is clogged if our coil is clogged, but we have no filter and that's why our coil is clogged, Where are we going to have? It's going to do the same effect and then it'll drop static pressure on our return and supply. Because we're not moving air, we're not moving as much air. air is getting caught here.

But where are we going to have a really extreme difference in our static pressure? Yeah, so we're gonna have a big drop across our coil. So in here there's going to be a much stronger, uh, vacuum. So we'll have a negative static pressure in here above the coil. The Blower's trying to pull.

It's not getting a lot of airflow through there, so it'll be a a much stronger pull here than if your coil is clean. Okay, so every coil does cause a bit of a pressure drop. It's usually less than 0.1 on a clean coil that's wet, and even less than that if it's dry. And then if you have any kind of clog build up in here, then the pressure difference between here and here is going to be pretty significant.

You're going to have over 0.5 typically up into an inch or more depending upon how clogged your coil is. So you have these sweet tubes that are designed to cut into the direction of the airflow and then on the side you have the little holes that actually pick up the the pressure because the pressure exerted is basically it's a space pressure. It's not the force of the airflow, it's not the direction of the airflow. Whereas if you just stuck it in there and the hole was on top, the static pressure would be greatly affected by how fast the air was flowing rather than the actual pressure in the space.

So you put it in and you aim it up into the airflow and the arrow shows you the direction of airflow. However, with most of the systems we work on, there's not usually enough air that that actually matters. This would be for like, a much larger system moving more air that if you don't have that direction right, it can throw it off. It's not something that actually affects it much for us.

Anybody see any issues with how I have installed this? We're going to turn. how's that before the filter? That's right. So I installed it before the filter and let's go ahead and look at our static pressure. This thing is refusing to run in full stage.

Yet this is the area Supply in the direction here. the uh uh yeah, the um, it needs to cut into the airflow. We have a higher static pressure resistance on our return side, but this is still before the filter. So let's just compare when we move.

That all right? So what's the difference there? Yeah, 0.14 2.3 two now I Want to talk about using this in Diagnostics So when you're using Us in diagnostic, you sometimes have a situation where you are checking across your filter. So you do this test, pull your filter out and see what kind of a difference that filter is making. If you're wondering if the filter is really restrictive, it's if it's too restrictive. you can do that and see what kind of static pressure drop you have.

Now the system is designed for a 0.5 as its Max static pressure real life application You you can. You can get above that. Once you start getting above 0.8 close to one inch of static pressure, you're going to start burning through blower motors. You're really cutting down your CFM your blower motor ramps up to try to overcome that resistance.

So then you're pulling a lot higher amps not as efficient of the system. Also, when that happens, that means we're under a much deeper vacuum here. so it's pulling in warm air into the different crevices. So as soon as you start getting, you know 0.8 or higher on your AC system.

There's lots of little factors that just start playing into making this a very inefficient system long term and so that could be changed by ductwork design or actually getting like a media filter. something that would cut down in our airflow restriction. So that's one way that you can use in diagnostic. You can also use it to confirm if there's a duck restriction.

So if our supply duct is restricted, then we're going to have a really high static pressure. As the airflow comes through there and hits that restriction, we're gonna have a crazy high static if something in our attic is collapsed on the return side. or if we have a duct in a trailer collapsed somewhere like internally. You know how sometimes the internal duct will just collapse.

You can. You can see that you can take a static pressure. You have a really high static on the return, sometimes full of water. You go further down the line or inside the house.

drop it down into return and you don't have nearly as much static pressure. You can see that there's a difference across the duct work and sometimes pinpoint most of the time. Visually, you'll find those things faster, right? So my favorite way to actually use this practically is when I have a coil that has been cleaned in place or maybe it froze and all the surface debris fell off with the ice. and I suspect that my coil is impacted.

but I I need proof You can't really see it? I Don't have a good angle to actually see through the coil. Sometimes the coils are this thick so you don't really know if it's impacted internally. and we got algae growing on a coil. You can do a pressure drop across your coil I'll leave this one in the return.

so this one is above the filter right below the coil, right right. and then you drill a hole in your compartment where the blower is above the coil and you put your supply one in there or whatever it is. You're just looking for a difference between the two. So now the unusual thing here is that both these areas are negative pressure.

Typically when we are doing our reading we have our our positive and negative and we take those two numbers and add them. So if we have minus two plus two, minus 0.2 plus 0.2 What's our total external static? It's four, not zero. We add them together. we have four as our total.

We have two resisting on the bottom side, two resisting on the top. That's a little bit different here if you look at your measure quick. These are both negative pressures and so the total external is going to be a little bit off. You just have to do the math yourself.

Okay, so I have a 0.31 uh, on below the coil and then 0.43 above the coil. So we have about a 0.1 drop on a wet coil. So if that coil is going to be impacted, you're going to have like over 0.5 of a difference. If it's pretty bad, it's going to be up at one or even more than that.

And that's because Above This the blower is going to be pulling so hard on that clogged coil will have a high static pressure negative pressure in this compartment. And then below. Here we have a really low static pressure because not a lot of air is moving through that coil creating that vacuum. So does that make sense? So this is going to be one of the best ways for you to practically use your manometer.

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 HVAC Ourschool.com which is our website in hub for all of our content including Tech Tips, videos, podcasts, and so much more.

You can also subscribe to the podcast on any podcast app of your choosing. You can also join our Facebook group if you want to weigh in on the conversation yourself. Thanks again for watching foreign.