So this morning i wanted to talk about just a single topic, a very simple topic which is filtration and we've talked about this before, but there's some things that i think we forget and also when we're talking with customers. We will often rush to the lowest common possible solution rather than thinking about what the best solution might be, and one of the most common questions we get from customers is come on most common question. We get from customers exactly is this filter? I use a good filter or what type of filter should i put in this unit, and what do we say, sam um, the good filters, the best the best filters um, what i've never heard that question before yeah? What let me, let me ponder this before i've. Just never come up, so it is actually surprising that i think uh.

We don't all have a consistent answer to that question and do you know why we don't all have a consistent answer to that question? Well, that's one reason because you kind of make it up on you as you go 95 of statistics are made up on the spot. That was a good one. That joke was like a puppy. It was a little rough.

I came up with that this morning. I wanted to repeat it. This is so funny wow. So the reason why is that there is no good one good answer.

There's no answer to what is the right filter, it's very specific to the use case, but when we think about or the particular application, but when we go to a particular application, we're thinking about what the right filter is, we do need to know how we approach It in order to give a proper answer and that's what i wanted to talk about this morning, so that way you have more confidence to answer that question. So, let's start with what are some things that we need to know in order to answer that question. What are some things we need to know in order to answer the question of what is the best filter to put in to a particular unit, yeah like what is it okay? So where is the current filter located right? Where is the current filter located? That's a good question: what else do we need to know, and so it could be a filter, back, filter back return, air grill it could be at the unit, could be multiple filter back return. Yep could be multiples all right.

What else do we need to know? What's the question, what what do we need to know what the question is, if it's true, what do we need to know in order to suggest to a customer when a customer asks - or you know just as part of our regular work? What is the best filter that we can put into a particular application? What is the right filter to put into a particular application? What else do we need to know any concerns? You could yeah, so you could understand. I understand why they're asking the question: do you have any respiratory issues right? The customer's iaq concerns so understanding the customer's iq concerns is helpful, but, let's just uh. Let's just say that we're not necessarily trying to tailor something to the customer, we're more so just trying to say we're trying to answer the question of what is the best filter i can put in this thing. We want to answer that question.

What is it, what what is the airflow, so i guess system requirements or understanding the system system, airflow yep. I would also look at the system design t-e-s-p. Now the the design tesp doesn't tell the whole story. You actually have to look at the fan curve.

The actual fan chart in order to know fully the effects of static pressure. But if you don't know the design total external static pressure, then you don't know how much headroom you've got to work with, and so just as a very simple thing to look at. Go to the air handler go to the furnace and look at what your design total external static pressure is right and then i would go ahead and measure my total external static pressure. What else could you measure to understand a little bit more about what filter could be right or wrong for this system? Are your gears turn i'm hoping at least your gears are? Turning before i answer the question, i'm trying to assess gears right now and i'm not really getting a lot of feedback go ahead, but you showed it one time in class that shows all the stuff in there is like an air analyzer of some sort, an air Analyzer so, okay, interesting so you could use and that and that's not a bad idea, and this kind of goes back to understanding the customer's iq concerns.

You could use a particle counter or an iaq meter and a lot of you have the temp top meter instrument. Whatever you want to call it, it's a tool that measures the air quality measures, um particulates in the air pm 2.5 pm10 co2 and vocs total vocs. That's what that measures. So you could look at that, and that would give you some sense of you know whether there's a air filtration problem.

But what else would we measure? Well, i think we would probably measure our current pressure drop across our current filter. That's in place because, generally it's going to be some filter in place, so pressure drop across the filter. Does anybody know how to measure pressure drop across the filter, how you use your manometer and you check right before and right after the filter? All the air is running yep right before and right after and a lot of people get real worked up about whether you put the positive or negative, but you know what it's going to give you a number and whatever that number is that's the pressure drop, whether It's negative or positive: who cares it's whatever? The differential number is across that filter? Don't get too worked up about it, so it's actually a really simple thing to measure. How would you do it if the filter is a filter back with a direct return? How would you do it if it's a filter back with a direct return? You just put one so you zero it out in the room right and then you take it and throw it in the return and shut the grill.

That's it that's hard. Isn't it really? Tough, really tough, and if you use the field piece wireless one, you don't even have to do anything other than literally just take it and throw it in the return. You know, like that's, pretty easy to do at that point right i mean i wouldn't throw it too hard, you might, you might break it yeah. I think they.

I think they've been fully tested to underhand tossage and into a duckboard return and to a duckboard return box, specifically because a little more spring to it, they have a lab where they test these things. All right flex would be fine, too yeah. If there's metal, then no um, so pressure drop across the current filter, and i wanted to mark this one, because this one is what we like to call quantitative, which means that i mean it's also. It also gives it's quantitative, because it gives a number a number to the actual real world conditions that the system is currently operating under now.

Obviously, if the filter is dirty as it stands, then that's kind of a dumb test. You just change the dirty filter right check it after the filter is already clean, but it gives you a really good look at this current filter that you've got. Is it adding in too much pressure drop and how much is too much pressure drop for a filter? Well, we can make up a statistic: let's make up a statistic right: there is no one answer to that. There is no one answer to that, but if you are over 0.2 there's gon na be almost no circumstance where that's not going to be a problem.

Now there are it's possible if your ductwork is so pristine, so enormous that you have almost no static pressure drop in your ductwork, but again for most of these systems. Again, this is our market, the type of equipment we work on point five is about all the headroom we've got, but, as we've seen, we've got air handlers we're putting in they have a design total external static at 0.2, meaning that their rating is based. On a 0.2 total external static pressure, that means that the filter alone takes up all of your static pressure. In terms of again, we say static pressure, total external static is what we're talking about, and that means the pressure that's being exerted on the return and the supply, so the pressure against the flow of air and again, if you increase your airflow in your system and Everything else stays the same.

Does your static pressure go up or down uh-oh? It goes up. If you increase your airflow, your static pressure goes up. You can't answer the question after i already give the answer. Everyone knew he was just waiting you're just waiting, yeah yeah wow.

Is this like dora, the explorer? What does the static pressure do very good? Now you have to ask the question: does the static pressure go up or down all right, so pressure drop across the filter? Normally you get above 0.2, that's a problem, but again remember. There is a lot of variables if the system is running low, airflow already, because it's in uh, dehumidification mode or in low stage or something like that, then you're not going to get a true reading. So that's got to be where it's supposed to be. You got to know something about what headroom you've got, meaning what your static pressure is designed for for the system and again there are cases where we can run the static pressure a little higher than what the design is.

But that's where you can look at the fan curve to know the effects, but regardless there isn't a system that works better under high static pressure and i'm going to give a caveat other than very old systems in which you actually had to add more static pressure. In order to get the airflow lower to where you needed it to be, but under normal circumstances, we're not working on those applications anymore, most of our systems are x13 and ecm blowers, and so, when you put more static pressure, more resistance to airflow, what does the Blower do ramps up right, and so now, nowadays we have kind of this moving target and so there's a lot of reasons why we want to keep our static pressure low and both in our designs initially, but as service technicians. When we show up we're kind of handed a situation, you know the answer to every question: isn't we'll redesign your whole dock system right now? Sometimes it is sometimes it does need redesign. Sometimes it does need upgraded, but when, when the customer is asking the question, what filter should i put in this? There isn't one answer and we should not give one answer.

If we give one answer, then we're not doing a service to the customer and if we see a system that especially if the customer is asking these questions, then we need to be looking at the way to provide the best possible filtration we can provide. Now, i'm not going to focus on different types of technologies. We've done a lot of conversations about that different indoor quality technologies that exist, i'm talking just in terms of filter media, so we're going to talk very generally here. So what happens when we take a 20 by 20 filter and we make it thicker? What do we do? We increase surface area which does what more filtration has less less air restriction, so there is less resistance for the same result.

So you get more surface area when you spread that out make it deeper. You have deeper pleats, so there's less pressure drop across it, and so that's good right. But here's another question: do we change the velocity through the filter by making it deeper through the surface area? We do we, we can be changing the face velocity? Yes, yes, we can, but the reality is is that we still if we've got an undersized filter, where the velocity moving through that box is too high by putting in deeper that doesn't solve that problem right and in returns we should really be seeing if we can Three three to five hundred feet per minute. Under most cases, that's velocity, that's just speed of air.

Now again when i say that you're kind of like well, that doesn't mean anything to me, but here's here's a very practical technician: assessment. If she's a whistling, then the air velocity is too high generally speaking right, but when you go and you hear a return, that's noisy. That's a good indication that you have high velocity when you walk up to the air handler. You can hear the thing whistling now.

It could be that there's a gap or a crack in the air handler, that's also a problem but different problem. But when you hear a system that that sounds loud and you hear that air noise, that's a good sign that you have high air velocity. My point being that we can solve a lot of problems by going to deeper media, because that drops decreases our pressure drop. But the fact remains that when we have too small a surface area that air is still moving fast and let's just use some real common sense here when air is moving fast, is it easier or harder to clean it? It's harder to clean it right.

Why? Because that air is going to move around gaps and cracks, it's not dwelling on the media as long it's not as easy to pull the particulate out of the air just to think of it really simply again we're just kind of using a mine picture here and So what do we want to do in order to filter air better? We want to have less pressure drop across our filters and we want the air to move more slowly over the filter period right and how do we do that deepest possible media biggest possible media? That's basically it deep and wide right now, when you get into the particular media type, that's where things like merv radio rating come in and so higher the number, the more stuff it's going to catch, and you can look at a chart that will kind of show You but again those numbers don't mean much to anybody. Our goal is to get the biggest and deepest filter in the system that we can get so that the air moves slow and at low pressure drop. And then we can decide what the appropriate media is to put in and the bigger and deeper we can make. It the slower and less resistance.

We can have the better the media we can choose in terms of merv the more resistant the media. Now are there media out there that aren't as resistant but still do a good job of capture yeah i mean like the infinity air purifier is an example of that, where you're using electrostatic charges and you're using iron environment and you're doing some other things in order To kind of boost that efficacy, but regardless outside of the technology size, depth, right, physical square feet, square inches of surface area and then square inches of media itself makes sense. So to answer the question for the customer: what's the best filter to put in this unit, what they're asking generally is: what is the best filter that i can put in that will fit in my current slot that the filter goes in right and what is the Answer to that question, the answer to that question is well: we've got to take some measurements and look at where you currently stand and see if we've got any headroom, because if what you've got in there is a hog hair filter, which is just the washable super Basic filter and you're measuring pressure drop across that now again you're not going to get much pressure drop across that. But let's just say you are because your air velocity is so high and then you look at your static pressure and you're already pegged you're already at 0.8 total external static.

You can't afford to put anything in addition to what's already in there in terms of restriction, but there's a lot of technicians who fault one way or another. A lot of technicians will say: oh you can't put in that merv 13 filter that'll starve a system of air that'll cause it to freeze up. Well, that's not true it could i've seen it before right. You've seen it before because you've seen a particular application where you didn't have enough headroom and static pressure and the surface area of that merv 13 was too small right.

But if i take a merv 13, that's a 24 by 24 on a ton and a half system. Is that going to be a problem? No, of course not because now you've got massive surface area now it also matters how things are installed. So, for example, we've all seen the filter back return, air grille, that's a big filter back return, air grill, but then right behind it is a duct. You know that's this big! That just is right in the center and there's no and literally it gets a dirty spot on the filter.

That's round like this we've all seen that so obviously you're not making the use of that entire filter then, and so now, that's you know, that's a problem, but in terms of assessing the customer situation, we have to look at these things. We have to understand where the current filter is because, obviously, if we can give them a better result than they're currently getting without any major surgery, that's great, but if they've got room and they've got a you know an overhead return, for example, where we could fit In a nice big, oversized, filter cabinet with four inch filters: that's not a super expensive add-on, it's actually a really good value for the customer and another nice thing is when you put a bigger filter in that, has lower pressure, drop and lower velocity. Guess another really big, or can you think of another really big benefit to that? You don't have to change them as often gold star for jessica? Yes, you don't have to change them as often and that's also a really good benefit, because some people will point out. Well, media filters are more expensive right, but a media filter a good one should easily pay for itself in terms of how often it has to be replaced and again, how do you know when a media filter needs to be replaced? What's that when it gets clogged right, but how do you know when it gets clogged up? You can do that and that's probably more practical right.

That's what we're normally going to do, but pressure drop across the filter is the real answer right. If you have a filter that doesn't have a lot of pressure drop across it, it's it's still doing. Okay, right again, i mean. Could there be exceptions to that? I guess when you're talking about a high quality filter, if it doesn't you're telling the customer, we just give them a monomer.

What are you telling the customer? I tell the customer. It gets dirty right or once a year, yeah you're not telling the customer to pull out their manometer and measure the pressure drought. They did actually used to make little indicators that, as the pressure drop increased, the ball would start to float and say that it was time to change it. Those are kind of cool.

We can just install monomers on every one that we have manometer's on every one right right, ma'am. Let me show you how to put measure quick on your phone. What do you feel supports this? Those activated carbon filters? Okay, so activated carbon um or charcoal filters are great uh. Carbon is an excellent technology.

It's a very simple technology. It adsorbs a lot of chemicals from the air, so things like odors and other vocs in the air. Carbon is great. There's a couple downsides to carbon.

One is - and this is actually from a very practical standpoint, those of you who see carbon filters out there in the field they look black to begin with, and so don't like man. This looks really dirty. We must have a smoker on our hands ma'am if you've been running a diesel truck in this house. I see your problem right here: yeah um, so that's a that's the obvious one, and so it's harder to visually tell when they get dirty.

But the other thing with carbon is that the carbon that's often used on these filters, especially inexpensive ones, isn't high quality and it doesn't really last very long. The effect doesn't last very long. That's also true of a lot of electrostatic filters where they'll rate them based on an electrostatic charge that they apply, but then that electrostatic charge doesn't last so yeah. They might work well for a couple of days, but then that effect wears off and so you're not going to get better than in a standard filter than just really good quality media.

There's good quality. You know fibers that are going to capture particles. Um. Do i love carbon? Yes, i i love it as a technology.

I think that it's an emerging technology, but the reality is, is that for as often as we're generally changing filters, it's probably not a huge effect. Now, if you're in applications like dennis office, we did some work in the dentist's office. Recently number there's a lot of a lot of eocs in the air. You could potentially use like a carbon pre-filter, a very low resistance, carbon pre-filter and then change it.

A lot um in the returns and then still use a big four-inch media in the systems and that's the technique that we employed and so the even the even the idea that you can never double filter. You'll, hear people say that you can never double filter. Never have two filters in series. Well, that's not true.

It's just a matter of what the static pressure drop is so as long as your static pressure drop isn't too high that it's driving up your static pressure on your system above the design. Then it's not. It's not an issue, and so you can do whatever you want in terms of filtration strategies so long as you have enough surface area and you're actually looking at this stuff and the things that we really care about in terms of how to make a filter work. Well, well, is we don't want to have the air moving too fast through it and we don't want there to be a big static pressure drop across and now, thankfully, those two things are directly related to one another.

So it's not that difficult to figure out when you've got a high pressure drop across the filter. It's not that the filter is bad. It's that you're running too much air through it. So you could take! You can buy one of those.

You know mega monster. Merv. 15 cherry bomb filters from home depot they've got the pleats like this in them and you can put it into a system that works great, but it has to be a low airflow system generally speaking or you got to use a much bigger filter, but the problem Is we think in terms of what fits in the slot? That's our mindset, the filter that goes in that unit is the size that fits in the slot, but that's not a good way to think about it. Sometimes the one that fits in the slot is okay, but, as i've talked about before these slots aren't designed very well for a lot of reasons, they're hard to get in and out, the doors are hard to get in and out the doors leak.

I don't really want to see us installing systems with regular filters in them. If we can help it because and truthfully, we should be sealing those filter, doors too, when we're done so that way, it's not going to leak around it and i don't care, probably probably thumb gum around the back edges or you know and then put it on To be fine or tape, or whatever you want to do, but we really don't want gaps and cracks gaps and cracks lead to moisture being drawn into the system. They cause condensation issues, gaps and cracks also result in bypass air, that's bypassing the filter and getting the coils dirty and the blowers are dirty and everything else. So in terms of, and we've talked about this a lot in terms of providing customers with good indoor air quality, i don't have a problem with some of these high-end out-of-the-box products if they're properly applied and if you understand them, but i do have a problem with Them if you're jumping to that without understanding the basics of filters, things like bypass air, you know if you've got a giant return.

Duct leak. I don't want you focusing on putting a bipolar in it right, you're, pulling in a bunch of crappy attic air into the house and you're trying to solve it with some product that you're plugging in. If you do everything else right and then you really understand the technology you're applying and you ask the right questions to the customer and you give them a product that they're going to understand is going to provide a good result. Then great.

But in terms of what i wanted to kind of pin down here is when the customer asks the question: what is the right filter for this unit? The answer requires a little bit of measurement all right. I took some measurements on the system and you actually can put in a little higher merv filter. You know be careful: let's look at some options, real, quick and kind of see what we've got and you can look like, for example, a lot of the off-the-shelf filters that you buy will give you a rating um, like i think, it's filtrate or flanders, one of Them right on there, it gives you kind of a guide from airflow for that particular filter and what the static pressure drop will be across it. I i got one from my house uh.

My mitsubishi upstairs is a regular vertical and i i was planning to grab a filter from the office and i was like oh crap. I forgot so i stopped in at ace and grabbed one, and i threw it in i'm like man. This thing is really screaming at me, so i pull it back out and look at the look at the little guide and based on the airflow of my system. It was like a 0.25 pressure drop new, so obviously that's not going to work and in terms of what we would like to see.

We would like to see pressure drops of one or less it's crazy when those filtrate ones like a 20 by 16 filter, like that, it's designed for like a maximum of like 700 cfm yeah and then it's high, and so knowing your system, airflow, which i really Like what jesse said here, knowing what your system airflow should be is a really great place to start now there are a lot of purists out there who say that you know you got to refer back to the manual j every single time and again, if you're Doing a new system install where you're responsible for the duct work and all this sort of stuff? Okay, that is a good idea, but for a technician in our market and i'm gon na get slack for this 350 cfm per ton is what we run and a lot of it is because we're dealing with very imperfect houses and we're not doing blower doors on Every house and solving every leakage problem and so we're trying to set up our system, so they do a really good job of latent removal and so 350 cfm per ton, generally speaking, is a good way to kind of gauge what a system should be. So if it's a 2-ton system, airflow is 700 cfm right kind of panicky there. So when we set up our equipment and we look at static pressure and all that and we set our pins and all that, that's what we're kind of setting it based on and then we're looking we're. Choosing a filter based on that as well.

But as far as you go because you're working on functional equipment, you don't have to overthink this, it's not like. You got to sit there. Well, let me pull out my calculator here. All you got to do is take your manometers.

What's my total static external static pressure, what's my pressure drop across my filter right now and it'll give you a really good indication of whether or not you've got head room to put in a better filter in this current slot? If you don't, then the answer is okay. Can we put in a four inch media filter on this piece of equipment easily? Can we put in a return filter? That's the three or four inch return filter that recesses in to the grille cause. That's a really nice option: can we increase the size of returns? Can we add returns, there's a lot of things that can be done to increase our filtration by decreasing our velocity and decreasing our pressure drop across our filters? Does that make sense? I don't want you to overthink it right now, as we go deeper into these classes. On occasion, we're going to look at how to do some of the math and some of the rules of thumb and all that and again for technicians, it's very different than designers or even installers, and as an installer, you do definitely need to be measuring total external Static pressure before you walk away from a system, sometimes i'm seeing this not showing up on reports.

It's a problem - maybe you just didn't put it in the report, but i guess my guess is that sometimes you're not checking it and total external static is something you need to be doing because uh, you really can't know whether your system's running efficiently at bare minimum, Whether or not you're taking, if you're not taking it and then also um in some cases, you're not going to even know what your airflow is, because you on a lot of systems when your static pressure starts to get too high. That system is not going to produce the airflow that it's designed to produce, even if it's an x13 or an ecm, because those curves start to tilt backwards as you get to higher static pressures, meaning they start to produce less airflow. I see more motor failures too. More motor failures, the motors run hotter the system's less efficient um.

It's just bad bad, bad, bad, bad. If a system has high static pressure and again, i know that a lot of times. We don't do these things because we don't want to know. You know, like.

Oh, i just finished the day and i'm used to getting done at three and now i've got high static pressure and i'm gon na have to deal with that right. But we got to deal with it because we can't deliver the customer a inadequate result. We can't deliver the customer system - that's not going to last because of that static pressure, cool any questions, no great have a wonderful week, 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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