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Thread: Return Location

  1. #14
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    Jun 2000
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    N. W., IN
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    1,017

    Hmm

    Going with the Rheem Mod. makes that a high-end system. You might also consider that if the 2nd fl. furnace is in the attic a single return is likely to be a filter grille whereas if each bedroom has return then you are going in the attic to change filters. I think of it as somebody may be trying to save money on material but if they do it's gonna' cost YOU.

  2. #15
    Join Date
    Mar 2004
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    171
    Ron, what do you mean by the last line of your post?

    I talked to the HVAC contractor today, and he insisted that this is the way he has always done houses and he has had no problems or complaints. My general contractor says he has used him for years and he is good. Methinks he is trying to avoid doing extra work. I had even offered to my GC to pay for the additional labor and materials on return ducts, but the HVAC guy said it is not necessary and that the flow under the doors (with hardwood floors and no rugs) will be fine.

    I am also concerned that this guy has told me that he installs Carrier, Trane and Goodman, not Rheem, but he will install what I want. I am not so sure he will get all the things needed for installing the Rheem mod. Any thoughts?

    Originally posted by Ron
    Going with the Rheem Mod. makes that a high-end system. You might also consider that if the 2nd fl. furnace is in the attic a single return is likely to be a filter grille whereas if each bedroom has return then you are going in the attic to change filters. I think of it as somebody may be trying to save money on material but if they do it's gonna' cost YOU.

  3. #16
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
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    From greenbuiler website:

    2.0 Airflow Factors

    2.1 Doors
    Opening and closing doors in a home has a significant effect on the operation of a ducted heating and cooling system. Supply registers are typically located in each room. Returns air grills (usually only one) are typically located in a central part of the house.

    The air that is supplied to a room with closed doors will overpressurize the room if the doors are not sufficiently undercut to allow air flow underneath (accounting for carpets). The room with the return air is then "starved" for air or depressurized.

    An unbalanced situation of depressurization and overpressurization leads to infiltration of unconditioned air and exfiltration of conditioned air, resulting in higher energy costs.







    But yes undercutting the doors will work,IF the cut is high enough for the air flow to the room,with a Master suite ,I haven't seen one that undercuts alone would work.


    I'll see what else I can find on this.


    Maybe print this off for him to read;
    http://www.fsec.ucf.edu/bldg/pubs/air_residences/



    This is from the same site as above;
    Return Air Pathways: It is important that there be sufficient air flow pathways for the supply air that is delivered to each room of a home to return to the air conditioner's air handler unit (the box with the blower fan). Otherwise, the part of the home containing the main return to the air handler unit will be "starved" for air, resulting in depressurization of this space with respect to the outdoors. If this occurs, outdoor air will be drawn through the small pathways that exist in the exterior building envelope. In hot, humid climates like Florida's, these air flows can result in the accumulation of moisture within the gypsum wallboard, especially if it has vinyl wall covering. This, in turn, can result in the rapid and abundant growth of molds — remember, the cellulose (paper) on gypsum wallboard makes an excellent, preferred mold food.
    If room doors are kept open, there will be sufficient return air pathways. However, if rooms doors are closed, the rule-of-thumb is that there should be about 50 square inches of "free" air transfer area for each 100 cfm (cubic feet per minute) of supply air to the room. In this case, the term "free" means a simple, clear hole in the wall between the room and the remainder of the home. If, for appearance and privacy reasons, this hole is to be covered by grilles on each side of the wall, then the overall return air pathway area needs to be increased by about 40% to account for the air flow resistance of the grilles, or about 70 square inches per 100 cfm of supply air flow.



    BTW ,it's code in Florida to have a return or return path in every room ,except baths and kitchens.

    [Edited by dash on 07-19-2006 at 04:40 PM]

  4. #17
    Join Date
    Apr 2005
    Location
    Finksburg, MD
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    193
    Thinking that since you are building a high end home and have selected a high-end furnace that by default all else will also be high-end it just plain naive at a minimum. Thinking that paying your contractor extra to run returns in every room is going to motivate him to do so also naive. Your HVAC contractor, if like most I have seen is thinking how fast can I get this job done so I can move on to the next. Also if you have selected a more expensive furnace, in order for his bid to be inline he will need to cheap out somewhere else. It's a damm shame but this is the reality of the situation.

  5. #18
    Join Date
    Aug 2002
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    One more;

    1
    The Problem of Pressure
    Paul H. Raymer
    TAMARACK TECHNOLOGIES, INC.
    Section 601.4 of the New Florida Building Code:
    “Restricted return air occurs in buildings when returns are located in central zones and
    closed interior doors impede air flow to the return grill or when ceiling spaces are used
    as return plenums and fire walls restrict air movement from one portion of the return
    plenum to another. Provisions shall be made in both residential and commercial
    buildings to avoid unbalanced air flows and pressure differentials caused by restricted
    return air. Pressure differentials across closed doors where returns are centrally located
    shall be limited to .01 inch WC (2.5 Pascals) or less. Pressure differentials across fire
    walls in ceiling space plenums shall be limited to .01 inch WC (2.5 Pascals) by
    providing air duct pathways or air transfer pathways from the high pressure zone to the
    low zone.”
    Without central air-conditioning, the South wouldn’t be what it is today. Used to be that
    opening the windows was the only form of relief in warm weather, and home builders
    had to consider how air would be able to move throughout the house. Cupolas allowed
    rising warm air to escape at the very peak of the house. Shutters allowed the air in and
    kept the sun out. Transoms allowed the air to flow between rooms even if the door was
    closed. (Transoms were also the stuff of mystery novels – peeking through key holes and
    listening at the transom.)
    Room air conditioners, installed in a window, made a single room a refuge from the heat
    in the rest of the house. The room needed to be closed off from the rest of the house,
    darkened by its window shades. If there were transoms, they needed to be closed if not
    sealed. For a new house, central air-conditioning became the option of choice and things
    changed. Chilled, dry air could now be ducted to and from each room making it
    comfortable throughout the house. Central air-conditioning makes it comfortable to live
    all year ‘round almost anywhere, even in places that only the mosquitoes inhabited in the
    past.
    To keep the installed costs down, it became common practice to put supplies into each
    room and use a central return, eliminating the individual return runs. It’s okay to use the
    rooms as ducts as long as all the doors in the house stay open. As soon as doors start to
    close, the system changes. Without the transoms, the air just can’t flow throughout the
    house when the doors are closed.
    Some rooms are pressurized and some rooms are depressurized. Air will seek to leak out
    of a pressurized room and leak in to a depressurized room. Even though air has always
    leaked into and out of houses, the reason it’s a problem now is because of air
    conditioning. The leaks may be very small and the pressures tiny, but even a slow leak
    over a long term can cause serious damage. The pressures are as small as a couple of
    carbonated bubbles popping out of a soft drink. But in a house, those tiny pressure
    differences just don’t go away.
    2
    Now that the walls have been nicely chilled by the air-conditioning, the warm, moist
    outside air that leaks into the rooms under negative pressure, slithers its way down from
    the attic or from the outside through the wall system until it strikes something that is
    below the dew point where it gives up its moisture. This can commonly be behind the
    vinyl wallpaper, which acts like a vapor barrier and the moisture can’t get through. So
    there, where it’s dark and damp and cool, the mold can slowly grow and not be noticed
    for a long time.
    If the system is balanced, there won’t be pressure variations. This can be accomplished
    by installing dedicated returns or the transoms, severely undercutting the doors (three
    inches or so), or using one of the alternatives such as a “jumper duct”, wall to wall grilles,
    or a baffled return air pathway.
    A “jumper duct” is simply a piece of duct that “jumps” over the partition. A grille and
    collector box is installed in the ceiling on each side of the wall, and they are connected by
    a short section of duct work. To keep the pressure below .01” wc (2.5 Pascals), the
    grilles should be connected by rigid ductwork, preferably 8” in diameter. If 8” flexible
    ducting is used, flows up to 100 cfm can be delivered to the room if the grilles are 2 feet
    apart or less. Using 6” flexible ducting, flows of 55 cfm or less can be delivered to the
    room. The bigger the duct, the smoother the curve, the easier it is for the air to move.
    Easier means less resistance, and less resistance means less pressure build up. Also don’t
    ignore the back pressure generated by the grilles. They should be as open as possible.
    For a simple, clear hole through the wall (no grilles), the hole can be sized using the
    formula:
    Area Sq In = CFM/1.7
    This assumes that the pressure difference needs to be .01” (2.5 Pascals). So for 150 cfm,
    the hole would need to be 150/1.7 or 88 square inches or (in even numbers) 12” x 8”.
    That would be a clear hole with no grilles. Adding standard, “return air” grilles, would
    allow only 85 cfm to be delivered to the room. To allow 150 cfm into the room, the
    pathway with the grilles would have to be 12” x 14”.
    To size the hole including the grilles:
    Area Sq In = CFM
    Not many people would really want an open, 12” x 14” hole in their bedroom wall. If
    they weren’t concerned about privacy, why did they close the bedroom door? An
    optimized, through-the-wall system is big enough to allow the air to flow through but
    includes a means to restrict the transfer of light and sound. Tamarack’s Zenon™ and
    R.A.P.™ products do this by including baffles that have almost no resistance to the
    movement of air, but impede the transfer of light and sound by forcing them to move
    through indirect paths.
    3
    If the building code allows it, an entire stud cavity can be used as the return air path,
    inserting a grille high on one side of the wall and low on the other. The effective “hole”
    of this arrangement is the area of the stud cavity, which is limited to 3.5” x 14.5” or 50.75
    square inches maximum. To allow a .01” wc maximum pressure difference and using
    standard return air grilles about 61 cfm can be delivered to the room using this method.
    The accompanying table can be used to select the best method at various air flows while
    maintaining the pressure difference at .01” wc. Knowing how much air is delivered to
    the room would indicate which method would be most suitable. For example, an 8”
    jumper duct could be used up to 100 cfm.
    Note that these transfer
    methods are additive so that,
    for example, combining a 6”
    jumper duct with a 1” crack
    under a 30” door, will allow a
    flow of 100 cfm to be delivered
    at .01” wc or combining a
    R.A.P. 12 with a 1” undercut
    would allow up to 175 cfm to
    be delivered. (It should be
    noted that door undercuts are
    under builder not HVAC
    control and that the actual
    dimensions are greatly effected
    by the thickness of the floor
    coverings.)
    Although the problem may
    seem complex, these pressure relief solutions are pretty simple. And once installed, the
    HVAC system will perform better, the occupants will be more comfortable, and the risk
    of mold or deterioration in the wall structures of the house will be reduced. It’s a small
    cost for a lot of benefit.
    August 2002
    TAMARACK TECHNOLOGIES, INC. (www.tamtech.com) is a principal team member of the DOE’s
    Building America Program and a member of the Home Ventilating Institute (HVI). Paul Raymer is a full
    member of ASHRAE (American Society of Heating Refrigeration and Air Conditioning Engineers).
    Max CFM @ .01" wc allowed by each solution
    0 20 40 60 80 100 120 140 160
    Jumper Duct 8"
    Jumper Duct 6"
    12" x 14" Hole
    12" x 8" Hole
    R.A.P 12
    R.A.P. 8
    Zenon 24
    Zenon 12
    Offset Grilles
    1" Crack 30" Door
    1/2" Crack 30" Door
    CFM



    [Edited by dash on 07-19-2006 at 04:53 PM]

  6. #19
    Join Date
    Jun 2006
    Location
    Richmond, VA
    Posts
    2,844
    My brother in law lives in another state. I designed the ductwork and gave it to the homebuilders sub. He changed his quote for the extras (like sealing the ducts using mastic and installing balancing dampers and a return in every room that has a door.) Put it in like I wanted and it works great.

    I hate the statement "because we always do it that way" There are better ways and if someone is willing to pay for quality then let them have it.
    Give a man a fish, he will eat for a day. Teach a man to fish, he will eat for a lifetime.

    Give a man a capacitor, doesn't know what to do. Teach a man to install it, now he knows everything.

  7. #20
    Join Date
    Mar 2004
    Posts
    171
    Thank you for the replies. Robertsc65 (if I got that right) hit the nail on the head. The HVAC guy is just plain stubborn and thinks that my house is Burger King and he can have it his way. I've gone round and round with him on the ducts and he ain't going to change it. Dash, I've been on the Tamarack site, and my plan is to drop the issue with the HVAC installer, let my general contractor know what I think of the HVAC installer, and address this later one by either having an HVAC company correct it or do it myself using hte Tamarack product. It's a shame it is that way, but I don't have the time or the energy to continue to battle this guy. When I asked him how much air is being delivered into each of the rooms, he replied "not that much to worry about" and when I asked about the CFMs in the master suite, he replied the same. What a guy. Since our children are still very young, we will not be sleeping with the doors closed, and this will not be that big of an issue until the kids are older and want to sleep with the door closed.

  8. #21
    Join Date
    Mar 2004
    Posts
    171
    A couple of more questions. If I do the aftermarket approach by Tamarack, how do I determine the amount of air being delivered to the room through the HVAC supply vent? And if I do not have any walls in the bedrooms against the hallway wall where the central return is, I will have to put in jumper ducts from the bedroom ceilings to the hallway ceilings or connect the returns to the HVAC return trunk. If I go the latter way, I will definitely hire a pro.

  9. #22
    i owuld have it done right now tell them this is your house and your money. and you want it done right or you will find someone else who will. play hardball with them and get it done right. do not settle for their lame ass excuses and lazyness tell them you a return in everyroom and that is it. if they wont do it youll find someone else who will

  10. #23
    Join Date
    Mar 2004
    Posts
    171
    thomefan, I agree to a degree, but winning the HVAC battle may piss of the general contractor, and I have a house to finish. Yes, it will be a pain in the ass to do it later, but cutting returns in the ceiling should not be such a big deal.

  11. #24
    i know but when you are spending as much as you are it should be done right not halh assed sorry contractors like that bother me i bid jobs the right way and they undersut me with that **** good luck man

  12. #25
    Join Date
    Mar 2004
    Posts
    171
    If you are in central NJ, I invite you to come out, because rather than pay this jack@ss to do anything extra, I'll pay someone who wants to do it and isn't go to try to bullsh!t me.

  13. #26
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
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    My guess is your HVAC guy just doesn't know any better,many on this site would admit that there was a time ,they didn't either,I know I would.

    Try this ,click on this link;

    http://www.tamtech.com/PDF/R.A.P.%20...L.%2008.02.pdf

    Same as above ,but the chart didn't come out above.The chart shows how many cfms the door gap and pass thrus can handle.It's a good idea to use thee combination of the two,and add 500 cfms as a asafety factor.

    Now print the chart and article for them,draft a letter requesting them to address it.might want topoint out that when the house is done,if they don't address it,it will be obvious,as closing the door will cause a noticable decrease in supply air to the room,often causes door to close when left standing open ,a few inches from being closed.

    Hint,hint!Easy way for a homeowner to see if they have this problem.


    Good luck!

    [Edited by dash on 07-20-2006 at 11:48 AM]

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