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Can You Use Larger Flex Duct On Smaller Register

  1. I've read a lot of posts hither about HO's duct sizing probably beingness too small. So, I was wondering: tin ducts be too big? Assume that all the duct sizes are balanced throughout a house so that all ducts are oversized by the aforementioned relative amount (i.east. thirty%).

    Also, I'1000 request more for the functional aspects. I realize installing duct piece of work that is needlessly oversized would be a waste of money. However, I would think that, to a signal, the labor would be basically the aforementioned merely the toll of materials would exist college.

    If there's no functional problems with counterbalanced ducts that are oversized, then my "proposal" is that it would be worth a picayune more than money for materials to reduce the risk of having undersized ducts and all the problems associated with it.

    I know people volition say that doing proper calculations volition ensure the proper duct size, merely these calculations seem inaccurate at times -- even with HVAC-Calc from what I've read in other posts. There also could be certain exceptions that cause a habitation to need large duct sizing, but information technology isn't noticed or compensated for.

    Thank you for entertaining my curiousity,

    Josh


  2. the simply fourth dimension a heat load is inadequete is when the oestrus load is performed past an unqualified person wheather or non hes been doing it 20 years or 1.

  3. Larger ducts reduce the velocity of the air.
    Found a system yesterday where the air was not coming out of several registers very well. Plant that the 'hack' had attached unit to large existing trunk lines ( 2 of them ), which lowered the velocity then that 1 line was not getting to the supply registers.
    At present its going to cost the owner over a $1000.00 to dedo ductwork properly.
    Ducts should be sized as needed for proper volume and velocity for the system installed.

    Promise this helps,
    Richard


  4. Manual d ,done properly sizes the duct system correctly.

    If you to "oversize" use a lower Friction Rate then determined by Man D.Or design to use the medium speed of the motor,sas recomended by Human. D.

    Or if variable speed ,just utilise a lower ESP than needed.

    Oversizing the duct,within reason ,minimum .3"WC TESP ,should not cause a problem,though other then being able to add together a more than restritive filter ,I don't see much value.

    Using .5"WC as maximum design,would offer lower operating costs on VS.

    Oversized ducts,too depression of a static ,tin can usually be stock-still by calculation dampers ,to increase the static and redirect the air menstruation,as needed.

    [Edited by nuance on 08-05-2005 at 02:34 PM]


  5. I don't see how big ducts could cause lack of airflow if all the ducts are balanced, despite being oversized. By definition, the air would not favor one duct path over another. The blower would motility a certain book of air -- whether it moves slowly through large ducts, or faster through proper sized ducts -- aforementioned volume of air is exiting the supply registers.

    Is having low static pressure harmful? Information technology seems it would require less work from the blower to motion the air.

    Where are my assumptions wrong?

    Thanks,

    Josh


  6. VS it seems needs a minimm corporeality of static.A standard PSC motor will deliver also much air flow at low statics.

    Either can be corrected with dampers to increment the static.

    At present in svere cases every bit "born" may have ,yous could have oversized ducts and grilles to the bespeak that the air "falls" out of the grille and doen't get distributed in the space well enough.Oasis't seen that in a home ,merely I did see it in a commercial remodel.


  7. QUOTE
    "Is having low static pressure harmful? Information technology seems it would require less piece of work from the blower to motion the air. "

    This would be a large waste of free energy. Fans are designed to operate confronting a pressure. A fan is considered at its "operating point" when at forty to 80% upwardly on its bend and to the right of the heal.

    Static pressure causes the air in the duct to flow.
    Velocity pressure is the result of air movement.

    If a Fan where allowed to run with no resistance it would be at its Max CFM with no Static pressure (0 In. Wc)

    Core


  8. Originally posted by bornriding
    Larger ducts reduce the velocity of the air.
    Found a organisation yesterday where the air was not coming out of several registers very well. Found that the 'hack' had attached unit of measurement to big existing trunk lines ( 2 of them ), which lowered the velocity so that one line was not getting to the supply registers.
    At present its going to cost the owner over a $1000.00 to dedo ductwork properly.
    Ducts should be sized as needed for proper book and velocity for the system installed.
    Hope this helps,
    Richard

    If you have a blower out of the furnace information technology volition overload the motor. Depending on its SP rated blueprint, too high an SP will crusade the blower bicycle to unload.

    There is a proper duct size, SP, and velocity for chief and branch runs depending on he blower blueprint and the awarding.

    It is bad application design work to overdo oversizing a duct systems. (Acceptable velocity is important...)

    http://world wide web.udarrell.com/proper_cfm_b...g_systems.html


  9. If you desire to oversize any ducts practice it on the return. Returns are undersized by many contractors which leads to equipment failure and air flow problems including noise. I oversize all returns for noise purposes merely.

  10. Originally posted by bornriding
    Larger ducts reduce the velocity of the air.
    Found a system yesterday where the air was non coming out of several registers very well. Found that the 'hack' had attached unit of measurement to large existing trunk lines ( two of them ), which lowered the velocity and so that one line was not getting to the supply registers.
    Now its going to price the possessor over a $1000.00 to dedo ductwork properly.
    Ducts should be sized as needed for proper volume and velocity for the system installed.

    Hope this helps,
    Richard

    Richard, if the existing duct system is otherwise in skillful condition, this problem could be resolved with transitions to smaller diffusers. This will increment face up velocity at the diffuser which is what determines the throw. Balance issues can be corrected past carefully choosing the diffusers and the installation of trunk-line dampers if needed. Smaller diffusers will increase overall static, but not as much every bit reducing the entire distribution organisation. But this is not a problem if you conform the blower to deliver the design cfm based on the new configuration. See comment #1 below.

    Also proceed in mind that a net render-side leak from areas outside the thermal envelope could exist contributing to the problem (pressurization effect can pb to reduced airflow at the supply diffusers).

    More to the signal of this thread: depression static and low duct velocity, in of itself, is not a problem. Here are some additional thoughts on the subject:

    1) More often than not speaking, blower motors are more efficient at lower esp's, given the same airflow, equally long as y'all're operating above the min recommended esp for the air handler.

    ii) If someone designs a low static system and fails to set the blower speed to achieve the design airflow, then the implementation is at fault, non the blueprint.

    3) Manual D provides an 'optimal' solution which minimizes the duct sizes. A smaller diameter distribution arrangement is slightly less expensive and sometimes significantly easier to install. Just in that location's no reason to downsize an already-installed duct system just considering it's larger than optimal!

    4) When downsizing diffusers, one must be careful where and how you make the transitions in lodge to avoid backlog racket.

    David

    [Edited by ginahoy on 08-06-2005 at 01:27 PM]


  11. There are situations in commercial where ducts are grossly oversized for noise command. Goggle box and recording studios. Just and so these systems are engineered to operate this way.

  12. Most of the replies here imply that a duct that is "likewise large" is bad...

    So how do you lot design a ductwork for a 2-stage system whose air menses varies by 40% or and then? If you size it for the college stage, won't the arrangement then be "oversized" for the depression stage, which most respondents say is bad?


  13. Good point.If our "all-time" arrangement reduces air flow that much with no bug,ducts would have to be severly oversized to have a problem.At present the two speed is near often used with a variable speed fan,so cfm is existence maintained.

  14. Originally posted by lginla
    Most of the replies here imply that a duct that is "too big" is bad...

    Then how do you pattern a ductwork for a two-phase system whose air menstruation varies by 40% or so? If you size it for the higher stage, won't the system then exist "oversized" for the low stage, which almost respondents say is bad?

    Sounds like you already know the reply: oversized ducts are non a bad affair. Only a minor hit for price, and perhaps some routing problems if y'all're running through a floor arrangement, etc.

    Having said that, if the diffusers are as well large, air throw may be less than optimal. Nonetheless, this becomes a not-effect in a properly insulated house.

    Finally, balancing, which is indeed important, can be achieved with an oversized duct system in the same style as with a 'properly' sized duct system (eastward.g., by selecting right relationships between various trunks, run-outs and difussers, and if necessary, using balancing dampers). See my before response, above.

    David


  15. Originally posted by dash
    Now the ii speed is most oft used with a variable speed fan,so cfm is being maintained.

    I assume y'all mean ii-stage, not two-speed? Just from what I see in manufacturers' brochures, they practise not maintain constant CFM betwixt first and 2nd stages. They maintain a abiding temperature rising, but the CFM varies by around twoscore% to friction match the increased heat output.

    Then I yet wonder how the other respondents who say that "oversized" ducts are bad because there is not enough backpressure or the duct velocity will exist too depression arroyo two-phase systems? Yous can't go in and manually conform dampers equally the unit of measurement cycles between beginning and 2d stage, can you?


  16. Originally posted by ginahoy

    Sounds like you lot already know the answer: oversized ducts are not a bad thing. Only a small-scale hit for cost, and possibly some routing issues if y'all're running through a flooring organization, etc.

    David,

    Thanks, and I want to agree with y'all , only most of the other respondents said that "oversized" ducts are in fact bad. So I am curious how they size ducts for two stage systems, with the variable air flow.


  17. Well,Carrier calls theirs a two speed,but yep information technology'due south really 2 stage.

    The constant cfm I'm refering to,is that a Variable speed delivers the cfm required,be it 80 or lx% of high speed over a wide range of external Static Pressures.A PSC motor doesn't do that,as the static is reduced it moves more air,if nevertheless on the same speed.

    Then issues ,if any ,due to oversized ducts, would be more likely with a PSC motor.


  18. dash,

    I understand that the VS will maintain the design cfm much better than a PSC.

    But fifty-fifty with a VS, it volition have a significantly different cfm between low stage and high stage, co-ordinate to manufacturers' specs.

    So how does one design the duct system (for the high stage, presumably), without having information technology go "oversized" for the low stage and its reduced air menstruum?


  19. How "oversized" are yous talkin nearly? A couple inches or feet? Oversizing a little won't hurt the arrangement. On Two stage systems, 1st phase is 65% this is why it distributes the air slowly & evenly in most cases.

  20. Originally posted by 2hot2coolme
    How "oversized" are you talkin about? A couple inches or feet? Oversizing a little won't hurt the system. On Two stage systems, 1st stage is 65% this is why it distributes the air slowly & evenly in almost cases.

    The original poster mentioned oversizing by nigh 30%, which happens to be pretty close to the CFM departure betwixt beginning and 2d stages of most units. And withal he got replies saying that this would be inefficient and grossly oversized.

    Just how else would one pattern the duct organization? If it sized "but right" for the second stage (high CFM), it volition exist automatically around 30% oversized for the first stage (depression CFM). See my question?


Can You Use Larger Flex Duct On Smaller Register,

Source: https://hvac-talk.com/vbb/threads/81742-Can-ducts-be-too-big

Posted by: bieberforripsy1951.blogspot.com

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