Your title sounds bass ackwards. Duct work should be designed for ventilation and conditioned air flow of the living spaces, not the AC.

very well put together

THank you soooo very much for this video! I am working on an old house that's never had HVAC and trying to figure out where to put the trunk line and ducts (unconditioned attic or 2nd floor in chases). So good to get a basic understanding of duct and trunk line sizes. Do you have a video of how to roughly figure out how many tons are needed? Thanks!!!

Good luck finding 7" ducting, boots, and collars.

You mentioned that your main duct/trunk has 1200 CFM, and you removed 400 CFM (appears to be 100 CFM / branch line). Aren't you removing the CFM as determined by the room size/load? That is: 100+200+300 = 600 CFM. The remainder left in your main duct would be 1200-600 = 600, not 800 CFM? Just curious where 100 came about. Awesome tutorial!!

Go with something a little more square once you factor in the outside dimension of the materials your working with your looking at 31”. You’ll be hard pressed to find a straight path 31” wide or tall through any truss system depending on how complicated the roofline is. 14x14 can accommodate the target cfm and velocity while being easier to maneuver through an attic and adapting to the cabinet of your equipment. Oh and don’t put a 6” supply in a bathroom that’s just crazy. If this drawing of the building is to scale based on the 4’ windows the square footage is no more than 1400. I can almost guarantee you do not need a 3 ton system for that size especially on a multi floor home with conditioned air above or below you.

Can you do a video on how to read an architectural drawing for a house?

If you're (or anyone in the know) still answering questions, how dobyou know the SP? Is that what the equip fan is rated at? Thx again

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 KZbin 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 KZbin 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!