Is it acceptable for the last branch duct to have a slightly higher velocity than the one before it? Wouldn't this cause backflow?

This is my favorite KZfaq video. Seriously. I've probably watched it about 20 times so far, just trying to get this information embedded into my brain. I've watched COUNTLESS videos here on KZfaq about Duct Design, Sizing Ductwork, Calculating CFMs, etc. You name it. But this video in particular, in regards to the specific information that I am looking for, has been the most informative. Hands down. (I graduated college 2yrs ago (for HVACR), and, although I have performed a few change-outs and NUMEROUS service calls, I feel like my next step to advancing as an HVAC Technician is to learn how to calculate heat loads and unit sizes, and sizing ductwork.) Thank you so much, @teachmeeverything3344, for the time and consideration that you have taken out of your busy schedule to produce such wonderful content. And thank you SO MUCH for not playing annoying rap or elevator music throughout the entire video. 😏

Excellent thanks

That a 2 ton system 28x8 is huge.. Your unit is only going to be 14 or 17.5 Also you should always start at the end and work your self back to the unit. This duct is tooo big you will have very poor air flow. Also if you dont put a Radius, fitting, at that first elbow.You are going to have significant pressure loss resulting in more lack of air flow.

Is friction loss the same as static pressure? My air handler has a “rated static pressure of .50inwg” and a “mad static pressure of 1.00inwg. How do the two correlate?

Sir this by far is the best video ever explained 👏 thank you so much 🙏

Dude, make the next one the cold air return! :-) Great Video.

In my country we use 3 ton in one room

can u show a video explaining how that plenum would be set up in a attic

This video is amazing and is answering lot of my basic questions about duct work planning. 👏👏

Thank you, thank you, thank you. My all male coworkers are cool and all but only so helpful. This info isn’t a fly by tutorial or something that in passing one can quickly grasp. But your video and my duct calculator will definitely be a gem moving ahead. God bless you!

this dude use his pipe poker for a pointer?

Awesome tutorial and great detail! Thanks! Only thing that would have been nice to add is notes on where/how to put the return ducts

Great video. Question is if you were to add zoned heating to this or any system would it affect or change this setup. I'm particularly wondering how it would affect a 2 zone system where you had upstairs and downstairs on two different zones? Do you need to change a bunch to account for flow and CFM, or is that why a bypass is added somewhere in the system to allow for limited flows? thanks for any help or explanation on that.

Very, very informative! I now can feel totally comfortable designing my own. Thanks so MUCH!!!

wow you need to sit through some Duct sizing classes, you have no clue about ACCA standards at all.

Great video! Question: how do you calculate the. LENGTH OF DUCT? example your 8x28? How far does this rectangular duct go?

Thank you for posting this. For laypeople like myself this is valuable information

how do you find the length of every supply duck and plenum

Nice video. Noticed you used a .08 FR for the main trunk line, but no the branches to the individual rooms.

This is one of the best explanations on this topic I’ve found!👍 Good shit bro , preciate you!

Thank you! Your calm, clear way of describing this is very informative! And along the way, you give us a tutorial in how to use a duct calculator. Much appreciated! If you have time to do another video, would you describe how to determine CFM's for various rooms, optimum register placements and the pros and cons of hard duct vs flex duct. I'm about to do a job for a client where the exterior wall of the living room faces south. The room has a vaulted ceiling, where the ridge beam prevents running ducts above the windows facing south. An option is to place registers high on the north wall in attempt to get air movement up and over to the windows and the south wall. The house is on a slab. Any thoughts would be appreciated! The layout of the room is similar to the 300 cfm room in your drawing, with the ridge beam running the length of the room.

Yup. Have to transition smaller each section to keep equal amount of velocity of airflow. I worked HVAC for 5 years.

Very good 👍

Would it be better to put a 4 ton or 3.5 to reduce the amount of reducing plenums u add ? or would u have to use a 3 ton due to the sq ft of the home ?

this was very edicational! the only thing i didn't understand was, on each of your trunk runs, how do you know how long to make each section of trunk? for instance, your initial trunk size was 8 x 28, but how did you know how many feet long to make it before dropping down to 8 x 20? i'm sure there is a logic there, i just missed it.

VERY informative and helpful lesson for the DIY person out here. I am curious, however, how the length of each section of duct affects the calcs and performance? Thinking shorter runs the better, but what do I know??? Also would love to see your process for designing the return side as well! TERRIFIC video...thanks so much!!!

Wow, that was an AWESOME explanation & AWESOME drawings!!! I’ve been wondering how they size ducts as I’ve been thinking about how to change how our 2 bedrooms are heated, to make it more efficient (don’t ask, previous DIY owner). I LOVED THIS video! THANK YOU!!! Your explanations as you go along are very easy to follow & understand, while being thorough! Not everyone has that gift. Makes me also better understand how potable water plumbing is sized too. And possibly how to get more velocity at my furthest faucet! Do they have the same slide charts for water pipe sizing??? Also, in residential heating with a natural gas, forced-air furnace, I use grate filters at the points of exit into the rooms to cut down on winter house dust. And I change them monthly. Is that stressing my heating system?

GOOD STUFF

I love cold air blowing on me when I’m dropping a bomb your wrong

I’m curious as to how this design process changes if one is trying to design a two floor duct system, under the assumption that the two floors are connected (in the sense that air can flow freely between the two floors via a staircase, for example).

Excellent video! Thank you.

Where are you getting your friction loss calculation from.... Rule of thumb? TEL,ASP,ESP? Plus loss per 100' of duct. I do love that slide rule though.

How many square feet is this house?

How did you find your cfm per room

For every 300-4000 CFM drop the main duct need to be reduced.

Thanks for the this video. Are those room CFMs total equivalent length and friction rate? Also, are they based on ASP or?

Excellent video. Thank you.

Probably a stupid question.. My air handler ( 2ton system) will be in the middle of the house. most of the load will be on one half ( 500 cfm's) and the rest for the other half.. Do I size the trunks coming off the plenum (tee) accordingly?? 500 for one side and 300 for the other. or is one a one size trunk ( 800cfm) straight down the middle and just branch off from there?? thx!!!

Thank you

Low velocity is only an issue if you don't insulate the duck work.

Best video I have found!

Thank you for the great video. I am wondering, though, does the calculation of the pressure drop not need to take into account the length of the ducts going to each room? The calculator says pressure drop at 100 feet length, but most of the ducts appear to be 15-20 feet long. In my house, the duct length varies from under 10 feet to 40 feet, and the result is artic winds blowing in one room, while the other only gets a light breeze. It seems to be designed wrong and I want to correct that, but wonder how to calculate the proper duct sizing vs. length

I have a masters in HVAC technical education and this method does not reflect proper duct sizing according to Manuel D. However, if you’re going to use this method, you need to put balancing dampers on every run or you’re going to have improper air flow. Sorry but don’t believe everything you see on KZfaq.

I have a masters in HVAC technical education and this method does not reflect proper duct sizing according to Manuel D. However, if you’re going to use this method, you need to put balancing dampers on every run or you’re going to have improper air flow. Sorry but don’t believe everything you see on KZfaq.

I have a masters in HVAC technical education and this method does not reflect proper duct sizing according to Manuel D. However, if you’re going to use this method, you need to put balancing dampers on every run or you’re going to have improper air flow. Sorry but don’t believe everything you see on KZfaq.

Maybe I missed it, but what is the square footage of this house?

Duct calculator a must ! Just started doing my homework on this stuff , explained & understood everything but the lenghts of each trunk runs before having to reduce ? 8"x 24" X ?. Im converting an abandoned hydronic on slab to forced air through attic.

excellent job explaining everything in details. I'm a Mechanical engineer by the way and currently doing HVAC Service residential. I really enjoyed the Video. thanks a lot.

Hey brother great video very good explanation , I live in Texas and we usually only use 1 sheet a duct board to make plenum and branch every run with flex. That’s 95% of Texas. Does this also work in that kind of designs? I’m a service technician don’t really do duct designing or manual J or D