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Thread: Duct Branching

  1. #53
    Join Date
    Aug 2003
    Location
    Central Kentucky
    Posts
    6,247
    Originally posted by Steve Wiggins

    No one that I know ever checks cfm at each register to see if it matches the designed value. [/B]
    Well now you know at least one person,trust me there are others.
    If we have a sizeable difference in how much CFM an area takes in heating & cooling we recommend zone controls.
    If you take the time to adjust your systems there won't be as many unhappy HO's.
    It is not about making the system perfect,this is not practical.
    What it is about is making your customers comfortable & making sure they are getting what they paid for.
    With that much confidence in your duct system design you should appreciate having it tested to verify your design has been achieved.
    All it would do is give more credibility to your engineering skills.

  2. #54
    Join Date
    Aug 2003
    Location
    Central Kentucky
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    6,247
    Originally posted by Steve Wiggins
    Originally posted by pjsullivan

    e. Flame is correct color, size, and burns properly.
    Peter I am very worried about this statement.

    1. What color are you looking for?

    2. What size is the right size?
    Steve I agree with you 100%.
    The only way to be sure an appliance is burning properly & safely is through combustion analysis.

  3. #55
    Join Date
    Feb 2004
    Location
    chicago suburbs
    Posts
    4,422
    Originally posted by Steve Wiggins
    Originally posted by davidr
    Originally posted by Steve Wiggins

    Dampers (for balancing purposes) are an engineers crutch and should only be used when the symptoms call for it. All the residential dampers I have seen are left wide open anyway so why bother and hamper air flow?


    how would an open damper hamper the airflow.




    Steve,I have to disagree with you on this one.
    Dampers are there because no design process is 100%.
    Things change in the field that don't allow the duct to be installed in the exact way the designer intended.
    There are too many variables that can take place which will affect air distribution for them not to be installed.
    If an adjustment needs to be made on start up to allow for airflow adjustment it is nice to have them there.
    Changes in the field need to be reflected in the design and not corrected by a bandaid dampering system.



    dampers are not band-aids they are valves. how else do you control the volume? how do you control the flow of water? with a valve (damper).



    No one that I know ever checks cfm at each register to see if it matches the designed value. The only reason a damper would get adjusted is if a HO complained and then when the seasons change they are uncomfortable again. They just get tired of calling the contractor about it and put up with the discomfort. All the while the contractor is thinking he actually fixed the problem. [/B]

    ..if the homeowner complained then a damper would be the ONLY way to re-direct the airflow. dampers are cheap and as long you don't bury them under drywall, they should ALWAYS be installed.
    FILL OUT YOUR PROFILE!!

  4. #56

    you have got to be kidding.

    I can't believe that PJ Sullivan is now trying to blame immigrant workers for this crappy duct design. First let me tell you that behind that desk designing these systems is an old us of a good old boy.I can guarantee you that the only language good old boy speaks is english and nothing else. Also parts lists are supplied from you guessed it the good old boy from behind the desk. The only difference you would have if you replaced the so called immigrant workers with 100% us of a good old boys would be very high employee benefits, sh##load of workers comp. Backed up on builders schedule and so on and so forth. You need a new job if all you do is use hard working people as scapegoats everytime you have to use your brain.

  5. #57
    Join Date
    Jan 2005
    Location
    Seattle
    Posts
    191

    Smile

    pjsullivan. I commend you on your efforts to do a indepth
    inspection for your customers.This is very rare around here.
    I have been in a nasty little crawl of a home a week after there closing to install gas pipe(hard pipe of course).Only
    to roll over and soak my shoulder in what was not quite
    just water. The 4" sewer main was leaking and there was
    a big white ring were the "water"had flooded and evaperated.
    How this was missed I don't know.I know of one home inpector
    around here who try's this hard.And sellers don'tlike him.
    But buyers love him.I have seen him cause people to get
    quite irritated. Because he really "inspects" a home.
    It seems to me the way for you to really check a hvac
    system would be to do what you all ready do.Than use the
    hvac-cal that is sold here.That and a air flow hood would
    very quickly put the ball in the installer court.Let them
    prove you wrong.You just got to know they went by a"rule of thumb".And that's before the installers whith very little skill,or thought to a job well done.And in a big hurry!
    Around here installers get a way with murder because of
    the mild weather.Back to back to back 6"dia. 90's going
    into wall stacks two floors up!!And the customer wants to
    know why the bedrooms up stairs are so cold all the time.
    It's called "hack and slash"here.I do mostly retro fit's
    And it can be a real bear to fix alot of this and make
    a buck at the same time.I love my trade a lot.And find
    some of this stuff very embarrassing.But I digress.Good
    luck with you efforts. And keep up the good work!

  6. #58
    Join Date
    Feb 2003
    Location
    Huntsville,AL
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    4,125
    again, ACCA manualJ is used to determine the load, given many physical parameters & the designer makes certain assumptions. manual S is used to size the equipment | unit. manual D is to design ducts for airflow necessary for the equipment and the loads. [ perhaps a local commercial plumbing shop will let you come & see manualD, one here did]

    Same info are in ASHRAE manuals [ ~$150 ea ], which have LOTS of design info; in 4 volumes, one updated ea year. [ Engr school libraries may have <1990 vintage, $$$ have prevented most from just getting them since then. In fact, none in a 400mi radius of me had one! including Purdue, GA Tech, ... ]

    regarding the ductwork, good insite can be gained just viewing the 3-4 pages of manD relative to "equivalent lengths" for the various fittings; eg: wye, tee, scoop take offs, etc.

    remember that air is a fluid which can be compressed.

    Leakage is a BIG concern along with duct sizing and its insulation.

    [Edited by cem-bsee on 01-09-2005 at 08:14 PM]

  7. #59
    Join Date
    Jul 2004
    Posts
    322
    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.
    I've heard that Chicago still requires cast iron drain pipes--no PVC--and armored power lines in the attic. That's good for plumbers and electricians, and I suppose makes for a better house. But I wonder, are Chicago's codes looking out for the trades or the homeowners? Maybe both.

  8. #60
    Join Date
    Nov 2004
    Posts
    125
    armored power lines in the attic
    No BX or romex except for 3'BX whips..all EMT conduit
    No pvc for DWV OR potable....cast iron and copper
    NO FLEX SYSTEMS...5'of flex or less and sheet metal required

    Yes Chicago protects homeowners and requires trades to know their stuff

  9. #61
    Join Date
    Nov 2000
    Location
    Memphis TN USA
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    6,945
    Duct systems can be designed and constructed without dampers.

    Dampers are for easy changes.
    If you add an addition for example, dampers can compensate.

    Too many people do not know how to design duct systems. They have a hard time balancing a system with dampers.
    If I had a digital camara, I could fill the wall of shame section with pictures 20 times over.

    Never could figure out how somebody was going to quess how much air is needed if they will not even do a load size.
    If the superheat ain't right it ain't charged right.

  10. #62
    Join Date
    Feb 2004
    Location
    chicago suburbs
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    Originally posted by tin_fab
    armored power lines in the attic
    No BX or romex except for 3'BX whips..all EMT conduit
    No pvc for DWV OR potable....cast iron and copper
    NO FLEX SYSTEMS...5'of flex or less and sheet metal required

    Yes Chicago protects homeowners and requires trades to know their stuff

    technically bx is illegal. greenfield is ok. ALL wire should be able to be replaced. from what i see and read on this board Chicago has set their construction bar pretty high compared to some parts of our country.
    FILL OUT YOUR PROFILE!!

  11. #63
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
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    18,836
    Originally posted by Steve Wiggins



    When I walk through a new construction house I want to see clean shiney metal inside the box with a nice clean metal elbow making the turn.




    5. No dampers. They are for inadequate duct designers and only hamper air flow.





    [Edited by Steve Wiggins on 01-09-2005 at 02:31 PM]

    Using a metal elbow ,instead of a flex one,only saves about 10 equivalent feet of duct.This has a very small impact on the FR or ESP.But to each his own.

    Although Man. D recommends dampers at branch ducts,we haven't found them needed.With a branch duct and grille velocity of 600 fpm or less,the damper at the grille can reduce air flow by 30% without a problem.

    With duct systems in hot attics,I doubt they would be used/adjusted very often ,in Florida.

  12. #64
    Join Date
    Dec 2003
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    Location!, Location!
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    To Tin-fab and Tinner 73-
    quote:
    --------------------------------------------------------------------------------
    armored power lines in the attic
    --------------------------------------------------------------------------------


    No BX or romex except for 3'BX whips..all EMT conduit
    No pvc for DWV OR potable....cast iron and copper
    NO FLEX SYSTEMS...5'of flex or less and sheet metal required

    Yes Chicago protects homeowners and requires trades to know their stuff
    --------------------------------------------------------------------------------



    technically bx is illegal. greenfield is ok. ALL wire should be able to be replaced. from what i see and read on this board Chicago has set their construction bar pretty high compared to some parts of our country.
    ___

    I also am in Chicago and isn't it a treat to see these installs? All flex and ductboard- the only time I got to do a job in that stuff, I think it took me longer because I had to fasten the stuff so that it didn't sag,seal all the joints and I took part of it out anyway and put in steel because I couldn't stand to leave it looking like that. I was probably way too picky. But I don't have an opinion as to its quality, if it is calculated for in man D., dynamics should work. I don't know that I'd ever use it for return, tho'. Yes, Chicago is picky, but we deal with it.

  13. #65
    Join Date
    Nov 2000
    Location
    Memphis TN USA
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    Originally posted by dash
    Using a metal elbow ,instead of a flex one,only saves about 10 equivalent feet of duct.This has a very small impact on the FR or ESP.But to each his own.
    [/B]
    Depends on how the pipe is run. A long sweeping flez line has less resitance than an elbow.
    If the superheat ain't right it ain't charged right.

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