Duct Branching

[-80guru]

PJ, how did you get in my attic? Seriously, That method used in the picture in my opinion is an abhorent way to install flex duct work. The Y branching method is fine if installed correctly. Is that amalgamation of ducts that I see installed correctly? NO! there is your answer. Is it going to be a problem? That is not a question anyone can answer except the technician who does an airflow analysis on that duct system. So tell your client to hire an HVAC professional to perform an airflow analysis. If that is not acceptable then you or anyone else cannot honestly answer if "It will be a problem".

[Steve Wiggins]

Originally posted by pjsullivan


"The HVAC ductwork in the photo, although branched correctly, may not provide adequate airflow to the smaller diameter sections of the branches. Recommend a qualified HVAC professional evaluate and determine a course of corrective action."

PJ, that statement is horribly inaccurate. You are going to have an a/c contractor dead in the middle of your xxxx.

Part of the problem here is there is no design requirement on the blueprints. You will find all sorts of other trades design but no hvac. The builders refuse to pay a design professional to draw out good design. Therefore all the decisions are left up to the installing contractor or his subs.

This notion you have of the smaller branches not getting enough air is weak. How do you know how much air should be coming out of the supply register? Even if you measured it with a balometer you still won't know because there is no requirement for that to be listed on the blueprints.

[mark beiser]

What it comes down to is whether the duct system was designed and sized properly for the fittings and materials used. I'll bet any of you a weeks pay that it is not, and the installer just tied all that together as the most convenient place to do it, using the least materials.

Ductwork run like that is very typical here in north Texas, and in my experience, is the cause of a lot of airflow issues.
Any time I see multiple wyes that close together in flex duct like that, I find badly uneven airflow.

At least they used metal wyes, those ductboard triangle things are total crap, and should be outlawed, lol.

[pjsullivan]

Thanks so much -80guru. I followed your advice, and informed my client that if he still has a concern regarding the ductwork, then he should contact an HVAC pro to perform an airflow analysis.

And thanks sincerely to all who replied. I will definitely be coming back here whenever I have HVAC questions.

[johnl45]

Originally posted by pjsullivan
Thanks so much -80guru. I followed your advice, and informed my client that if he still has a concern regarding the ductwork, then he should contact an HVAC pro to perform an airflow analysis.

And thanks sincerely to all who replied. I will definitely be coming back here whenever I have HVAC questions.

Now your acting like a true professional, good job.

[pstu]

A question I hope one of the more expert people will answer: Is the problem with this picture, partly that the Wyes are so close together? Can anyone explain why triangle boxes degrade airflow?

What can you see that will degrade airflow? Can you describe in a few words how it would be built better?

If there were a clear and simple answer, and the price were not thru the roof, I would probably pay to have it corrected in my own house.

Thank you -- P.Student

[dash]

There is nothing wrong with the wyes,or even tri-boxes,IF they are accounted for in the Man. D ,duct design.

In this case we have no information,to make a decision,as to what the airflow will be.

If you want to redo your duct system,it's Man. J,room by room,then a redesign using Man D.This will allow you to bring the ESP down to whatever you select,and provide even temperatures throughout the home.

[tinner73]

flex duct degrades the airflow. it is not smooth like the metal pipe. the smoother and squarer the duct, the better. the part here that gets me is even if you went with CHEAP round "stove" pipe it would be way better than this. it would be fairly close in price and you wouldn't need a
tin-shop. this way saves on labor mainly and what's more important than their bottom line anyway. i'm happy they don't do this around Chicago.

[pstu]

Dash, I have always consistently heard that message from you, "Manual D is the only way to be sure". Thanks for reassuring me that the universe is governed by natural laws and not by whims.

Although after the system has already been built, would not a flow hood test of each supply register (and maybe the returns too) give a valid after-the-fact answer?

Best wishes -- P.Student

[dash]

Originally posted by perpetual_student
Dash, I have always consistently heard that message from you, "Manual D is the only way to be sure". Thanks for reassuring me that the universe is governed by natural laws and not by whims.

Although after the system has already been built, would not a flow hood test of each supply register (and maybe the returns too) give a valid after-the-fact answer?

Best wishes -- P.Student

Testing would give you the total airflow delivered,thru the supply and return ducts,less any duct leakage.

This is valuable information,but you need to know what each rooms cfm should be(Man J),and what is the airflow thru the equipment(ie. without leakage).

[dash]

Originally posted by tinner73
flex duct degrades the airflow. it is not smooth like the metal pipe. the smoother and squarer the duct, the better. the part here that gets me is even if you went with CHEAP round "stove" pipe it would be way better than this. it would be fairly close in price and you wouldn't need a
tin-shop. this way saves on labor mainly and what's more important than their bottom line anyway. i'm happy they don't do this around Chicago.

Flex is not a problem,IF the Man.D design is for flex.Flex does not degrade airflow,poor design and install does.

[conrad1]

You are on the right path /do have an HVAC company check the design airflow airflow airflow 2nd only to unit size in importance the pic you showed actually looks better than most but that does not mean it is sized correctly to the unit or that the unit is sized correctly to the bldg. location have a manul j and manual d calc done

sorry dash I had not read the 3rd page before I posted you already settled it apologies for the redundancy

[Edited by conrad1 on 01-09-2005 at 11:59 AM]

[dash]

Looking at the photo,I'd check to make sure the wyes are insulated properly.