Shouldn’t the size reduction be installed immediately after the 5th takeoff? I know that the sketch is not to scale, but the sketch shows it midway between the 5th and 6th takeoffs. It might be helpful to illustrate, or mention, that the transition can be placed a short distance after the 5th takeoff to save materials.
I am adding 800 sqft to my home (1,400 existing + 800 new). Got quotes from 5 contractors so far. They are telling I need to upgrade my furnace and AC. The recommendations range from 3 ton to 5 ton.
Are they doing a actual load calc? If not dont pick them.. Also Dont pick 1 unit to do it all. No house can use 5 Tons. Maybe 2 2 ton units but never 5 tons out of 1 unit
Could you? Yes, that’s a rule of thumb that will solve for a volume that is greater then what Manual D produces l. The worst thing that’s gonna happen is you’re gonna end up with a duct that’s larger than necessary and as we all know, there’s no such thing as a duct that is too big. Following the guidance of Manual, D is the best alternative.
Hi Ed! I have a question about EL! Imagine that! Anyways, out in the field I am running a supply trunk & tapping off with saddle taps/dampers straight to the supply registers. In the Wrightsoft program that I am using it seems to give me multiple options but all with different EL. Option (A) Tee, no transition (B) Branch EL of round take-off (C) Trunk EL of round take-off. WHICH ONE DO I CHOOSE?! Thank you in Advance!
Group 2 page N22 in Manual D has your answer. The EL is relative to where the tap is with reference to how any branches are downstream to a trunk reducer or end cap. fitting NP is what I would use.
What is the equivalent length for a round pipe attached directly to a plenum in a return air system with a referenced velocity of 700 pm at 0.08 IWC per 100 feet? How to calculate, can someone explain thank you
Question: I have 17 feet of 6 inch duct supply to a room. After 17 feet, it elbows down and to the right, travels 2 feet straight, then elbows up and into a transition piece that feeds the room. Do I need to reduce the 6 inch to 4 inch OR simply get rid of the elbows and install a 45 set about 4 feet before the transition piece into the room?
Hi Ed I have a few questions for you. 1. After you reduced in the example.. won’t your last few runs “run out of velocity” on the end? (Just like when you took off your velocity dropped in the beginning?). 2. Is it acceptable when using round pipe to reduce 4 sizes if need be? I.E. let’s just say that I started with a 16” round pipe and at half my velocity I needed to reduce to a 12” pipe. Would it be acceptable to put 2 reducers together and go from a 16” to a 12”? Thank you
Question 1. No. Velocity can not be to low in a branch run if you follow the guidance of Manual D. If CFM is correct the velocity if air going through the terminal box and grille is what we care about. Question 2. Yes. Manual D is about having enough fan pressure to overcome all pressure drops, having ducts large enough to not allow velocities to go above maximum values and using dampers to get the proper volume through branch runs. There are a few more but thay are my top 3.
Thank-you! I’m not an HVAC expert, just an old, retired soldier, systems engineer...and woodworker, trying to keep the wood dust out of the air - and now, the smoke from all the wildfires in Canada, Michigan, Pennsylvania... I’ve been trying to get a better handle on “pressure loss” across a furnace filter. I’m having trouble finding data. I’m also wondering about the surface area of the filter media in different pleated filters, different thicknesses, and different MERV classes. Recently noticed that a five inch MERV 13 filter appeared to create a much greater “restriction” or pressure loss, than expected. Any guidance would be most appreciated. Thank-you!
I simply took the equation provided in Manual D and put it into a spreadsheet. Enter in the values and it automatically adjusts the EL value. Very handy to have. Especially if you end up with a friction rate value that isn't 0.08 inches wc or want to size based on a lower velocity than 900/700...or both! You can play around with different values to bring down large values and "dial in" a duct system.
3m/Filterate definitely do not publish accurate 'initial resistance value (WC)' that they print on their products. If a real consumer advocate group tested their products, they would be forced to change the printed information to double or triple those figures at those CFM ratings. I am an HVAC business owner and have tested these filters in numerous MPR/Merv ratings, plus different system designs and they are not even close to those numbers. I easily saw double the values printed in every system tested. Unsuspecting people put those in their furnaces or air handlers thinking they struck gold, but they got fooled by fancy wording. They are junk and it is best to still with a better filtration system instead of wasting money on that garbage. But all brands should be forced to print some accurate data just as the EPA makes companies put out accurate information for items they regulate. False advertising at best, but really it is fraud. Love you videos, btw!!
Thanks Kevin. If you want to go down a fun rabbit hole find ASHRAE 52.2. That is the standard that filter manufacturers are required to test PD and MERV ratings. This might explain the discrepancy that you’re seeing. Many filter manufacturers publish. Their pressure drops at velocities that are two or three times less than what we measure in the field. I have another video that says something about filters, if you haven’t watched that one I explain some or maybe even all of what I just wrote. And I’m not going back to proofread this this is voice to text figure it out lol.
@@edwardjanowiak Thank you for responding. I am a huge fan of our teachings online on the taped videos and your persona channel. You have really changed the way I view heating and cooling. And your humor makes it great to learn. I will definitely look into that ASHRAE 52.2 and read up. I look forward to it. And I think I only have a couple videos left of yours to watch but might go back over the big conference videos that were like 2 hours each. 20 years in the field and I always still try to learn more each day. You have given me some valuable information and I thank you.
Im so confused. WHAT IS FRICTION RATE? I've been researching for hours, and I don't understand this term. You also brought up a good point, how can we determine what filter the system can afford??
Hey if I put supply grills straight into duct 24x10 does the grill size let say 10x6 have the same cfm as say a 10x6 square duct not sure on how to size with grills going straight into trunk line thanks for any response
I've been trying to learn how to do basic calculations on what size ducts are suppose to be on an existing unit. I'm a service tech and never really learned about the duct sizing and sizing of a unit. I need to know these things. It's so beyond frustrating to me because I feel like I'm so lost. Every single video I've ever watched it almost seems like the people teaching are teaching in a way as though the students already knows most of it instead of teaching a 5 year old this stuff. I wish there was like an extensive three or four hour video starting from the very very basics. When I go on a service call and a customer complains that their room is always warm, I want to know if the unit is sized right and if they have the proper air flow going into their room. I'm at the point now where I'm about to just give up because I feel like there's so many missing pieces.
Where did you find the .03 value for supply outlet and for the return grille? Is this the sum of the grilles in the total system or the sum of the grilles along the total effective length or some type of standard value, as I see it everywhere in pressure loss discussions???
You obtain that information from the grille and register manufacturer, you’ll find it in their performance data or engineering data for the specific grille or register that you’re going to use. That pressure drop that is included is the one grille that is in the critical path or the longest circulation path. You can have multiple grilles if you’re doing a central return and you’re using transfer grilles.
Hi Ed just makin sure now, the friction rate is on each manual of the air handler depending on the speed of the blower? And we have to match that friction rate based on how we calculate sp, pressure drop, equivalent length, etc after the design is complete correct?
No, we use The blower performance chart that’s included in the air handler as part of the process to calculate our friction rate using the guidance of Manual D
We are getting a new HVAC system and they guy is insisting on putting in a 1” or 2” filter. I thought a 4” filter provided the least static pressure, and thus would maximize the life of my system. Who’s wrong? Thanks for the great info in the video!
Need more details, but most likely you are, unless you told him you were okay with adding another return. It’s possible your blower doesn’t have the power to overcome the pressure drop of one 4”. You solve this issue by adding multiple returns, lowering the pressure drop of the 4” to something your blower can handle.
@@winstagram1785 Thanks for the info! Totally makes sense. However, it turns out we had a miscommunication. The new 2" filer is 28" x 30"! So there is about the same sq. ft. of filter material in that as there is in a good 4" filter of the size it's replacing. So I'm happy with it. Feels like the larger size is a benefit somehow, but I can't quite settle on a specific reason...
Please explain Mr. Janowiak, what exactly is Effective length? Is it the amount of air we are losing or the amount of air coming out of the blower motor?
EL or more correctly put effective length is part of the TEL calculation and that is how we solve for the longest circulation path that is part of calculating your friction rate.
When I tell people how large their filters have to be they look at me like I’m a purple polkadotted unicorn with warts growing on my face. Before high school my father was teaching me to size a filter at 200 or below face velocity Per square foot. More people need to make more great informative videos about filters and face velocity and pressure loss they are greatly needed. Placing two or three large filters in parallel should be the norm not the abnormality
It's your choice. The #1 rule to follow is whatever CFM volume you are moving through the duct (in that section) should not exceed the velocity limit as per table N3-1 Page N13 of ACCA Manual D (it says 700 FPM for a return duct). Lower velocity will never hurt your perforce, but it can impact your cost. I size my ducts following the conservative path listed in the table mentioned above. Check out ACCA.org, click on the education & events tab to see where I'm doing my next virtual or live training event.
I do teach. I just started with ACCA so watch their offerings for classes in the fall. I am doing a psychrometric class (virtually in a few weeks). There is more of my content (RU-vid) on hvacairflow.com
Ed, were you previously with Eastern Cooling council and teaching the continuing education courses for the required hours to maintain hvac master contractor license?? If you’re no longer doing that is there anyone you recommend??
Question. Is it ok to reduce the duct work (let’s use your example) after we take first 3 branches, when the duct work is in unconditioned space to reduce the use of the materials and reduce the surface area of the duct work. So we can save few dollars on insulation and metal and also few BTUs?
Eduard Khachaturyan yes, you can reduce the size as much as you want. Just make sure you keep your velocity under the maximum limit. My observations have been when people use rules of thumb to size ducts, they ignore velocity limits and we end up with an undesirable increase in static pressure.
Hey Ed, what are the consequences of falling outside of the Acca wedge friction rate chart? That is .06-.1. This happens often when I try to size a duct system for a low pressure ducted mini split. Or with a conventional unit when my duct system is too long due to a tight, large custom home. Thanks!
Bruce Randall if the friction rate is low, you’ll have inadequate fan performance. If on the other side of the wedge you’ll have excessive velocity. Take a peak www.hvacrschool.com/the-friction-rate-chart-and-what-it-means/
@@edwardjanowiak Thanks for the reply. This is something I’ve tried understand for a while. Brian in that link says it helps keep the duct at a reasonable size. I can see that. But what is so magical about .06 - .18. Your tel/asp is what it is. Shouldn’t bigger ducts still deliver the correct amount of air? Or maybe Is the calculation of fitting length dependent on the friction rate staying between .06-.18?
@@brucerandall198 One of the phrases I've heard used to describe it is rate of return. You start to get into a situation with the lower friction where the duct work is physically too large. And the issues with that can be cost, whether it fits and one of the worst ones is that air moving at a velocity low enough to increase the temperature drop and or lower your supply temperature to the point where it causes the surface of our duct insulation to go below dew point. On the higher end with friction rates that end up being greater than .1 we end up with velocities that break “the rules” and we end up moving our duct slide to get our velocity within the limits so it's kind of a waste of time during the design process. If I calculate a friction rate of .14 and every time I line up my duct slide friction rate to my required CFM and I end up with velocities that are 1 1/2 times my limit it's an exercise in futility to continue to use that friction rate. The practitioner would be better off spending their time making sure that their available static pressure is somewhere between .2 and .3 (or do your own math and find a good Compromise on ASP) so when we use our duct slide we come up with realistic sizes versus velocity. I don't know if you did this on purpose, but I think you gave me an idea of the subject of another video.
