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  1. #40
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
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    11,376
    Quote Originally Posted by paul42 View Post
    Some shots after I lined the chase with drywall, mastic and caulk.
    The first picture is an overall view from the main room.
    The second picture is a closer view of the return vent opening from the main room.
    The third picture is a close view of the return vent opening from the side room.
    The fourth picture is of the back side of the chase from the closet.
    Fourth pic...looks like a fur-down was framed for a return...in the closet? I also see potential nailing problem for ceilingdrywall at that location...no nailer adjacent to fur-down, and nearest joist is at least 12-16" away. Drywall will essentially "float" in this corner, and over time the seams may split or crack.

    Pics showing return air openings...why the obstructions? Looks like drywall in one pic and a framing member in another. If the structural load can be or is transferred around that framing member, then IMO it would be better gone. Same for protruding sheet of drywall in other return air opening. It needs all the free area possible...looks a bit light as is.

  2. #41
    Join Date
    Jun 2001
    Location
    DFW
    Posts
    684
    Thanks for the input!

    I will check to see if there are places where I need to add some drywall nailers to the outside of the chase this evening. I added several to the inside of the chase while I was putting in the drywall liner.

    The obstructions in the return air vent openings are not an issue. The return air duct at the bottom is a 14 inch flexible duct, or about 154 sq. in. The free opening area of the vent into the front room including the obstruction is about 170 sq. in. The free area opening into the other room is about 140 sq. in.

    It would take some very restrictive grills to make that a problem.

    The air velocity in that return air flexible duct is higher than I would like. I may end up replacing that flex duct sooner than later.

    If I had gone to the trouble of specifiying things like the maximum allowable air velocity in the return air duct, I would have scared off all of the bidders (instead of just 6 out of 7).

  3. #42
    Join Date
    Jan 2004
    Location
    Here and there
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    4,808
    Paul, with all due respect, are you playing a joke on the folks here ? What it seems you have is a total wreck as far as a duct system goes.With a full basement why not run return trunkline and do it right? If the house is that tight why no discussion on an ERV ? There are a lot of issues to be addressed. No offense intended but I believe your " budget" dictated your choice in contractors and talking to the installers was next to impossible as they likely dont speak English. Best of luck.
    i belong to peta ... people eating tasty animals. all my opinions are just mine.

  4. #43
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
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    11,376
    Quote Originally Posted by paul42 View Post
    Thanks for the input!

    I will check to see if there are places where I need to add some drywall nailers to the outside of the chase this evening. I added several to the inside of the chase while I was putting in the drywall liner.

    The obstructions in the return air vent openings are not an issue. The return air duct at the bottom is a 14 inch flexible duct, or about 154 sq. in. The free opening area of the vent into the front room including the obstruction is about 170 sq. in. The free area opening into the other room is about 140 sq. in.

    It would take some very restrictive grills to make that a problem.

    The air velocity in that return air flexible duct is higher than I would like. I may end up replacing that flex duct sooner than later.

    If I had gone to the trouble of specifiying things like the maximum allowable air velocity in the return air duct, I would have scared off all of the bidders (instead of just 6 out of 7).
    Having now once again looked at the original photos and then of your modifications, I now see why the obstructions are there, and that they are pretty much immovable.

    Nevertheless I think I would've just flipped the return grill collar to vertical vs. doing the fur-out/fur-down into the closet. I've seen plenty of rectangular return grills run with the long sides vertical. I don't see how much difference it makes in appearance, but in your case it would give you more free area, and you could lose the fur-down in the closet.

    What is the tonnage of this system, again?

  5. #44
    Join Date
    Jun 2001
    Location
    DFW
    Posts
    684
    Quote Originally Posted by jpb2 View Post
    Paul, with all due respect, are you playing a joke on the folks here ? What it seems you have is a total wreck as far as a duct system goes.With a full basement why not run return trunkline and do it right? If the house is that tight why no discussion on an ERV ? There are a lot of issues to be addressed. No offense intended but I believe your " budget" dictated your choice in contractors and talking to the installers was next to impossible as they likely dont speak English. Best of luck.
    No jokes.

    When the total CFM for a 2,230 sq. ft. house is 800, a return trunkline is way past overkill. Not that I haven't already done some of that on this system.

    In this part of the country, an ERV would not pay for itself before it wore out. They are just not very efficient at recovering the latent energy that is a very sizeable chunk of our energy costs. The total energy cost for this house should average well under $100 a month. An ERV isn't going to make enough dent in that to ever be worthwhile.

    It turns out that the HVAC installers are all white Anglo Saxon English speaking men. They are just used to installing everything in the attic.

    "BUDGET" is one of the realities I must live with. We do not plan on ever moving out of this new house - but we must also be intelligent and consider the unexpected. No decisions are made lightly.

    Anything that is added to the house must have a reasonable payback, add appreciable comfort, add resell value, make a real dent in maintenance, or be a necessary part of our way of life. An ERV or a return trunk line were both considered, but they do none of the above.

  6. #45
    Join Date
    Jun 2001
    Location
    DFW
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    684
    Quote Originally Posted by shophound View Post
    Having now once again looked at the original photos and then of your modifications, I now see why the obstructions are there, and that they are pretty much immovable.

    Nevertheless I think I would've just flipped the return grill collar to vertical vs. doing the fur-out/fur-down into the closet. I've seen plenty of rectangular return grills run with the long sides vertical. I don't see how much difference it makes in appearance, but in your case it would give you more free area, and you could lose the fur-down in the closet.

    What is the tonnage of this system, again?
    The central system is 2 ton.

    The original work the installer left had even more obstructions than I ended up with. I removed a couple of studs and added others outside of the vent area appropriately.

    I considered running the grills vertically, but the aesthetics of the horizontal won out. As you suggested, I did add a drywall nailer on the one side of the fur down. With a ten foot ceiling in that closet, the fur down doesn't cost any valuable space.

  7. #46
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    Jan 2004
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    Paul , your just wrong.
    i belong to peta ... people eating tasty animals. all my opinions are just mine.

  8. #47
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    Jun 2001
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    DFW
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    Quote Originally Posted by jpb2 View Post
    Paul , your just wrong.
    My wife tells me that all the time

  9. #48
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
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    3,304
    Quote Originally Posted by jpb2 View Post
    Paul, with all due respect, are you playing a joke on the folks here ? What it seems you have is a total wreck as far as a duct system goes.With a full basement why not run return trunkline and do it right? If the house is that tight why no discussion on an ERV ? There are a lot of issues to be addressed. No offense intended but I believe your " budget" dictated your choice in contractors and talking to the installers was next to impossible as they likely dont speak English. Best of luck.
    I will second that opinion that an ERV does not do a whole lot in a hot-humid climate. Simple fresh air intake will provide ventilation with the AC having an opportunity to condition it better than an ERV would. If a dehumidifier could be put in the picture that would improve humidity guarantees, especially in mild spring and fall weather.

    To Paul42, have you considered looking up a copy of ACCA Manual D and working on the duct design? I am a homeowner myself and don't have the experience, but can testify Manual D is not too expensive and is readable. It would also be very nice to obtain a Manual J heat load calc to know what airflows will be required. The software from this site is cheap enough and easy to use.

    Best of luck -- Pstu

  10. #49
    Join Date
    Sep 2001
    Location
    Vancouver Canada
    Posts
    996
    Return trunk too expensive? Flex duct in this situation is a waste of time and money. Return duct will give far better flow charactoristics. As far as an HRV or ERV, it is not there for return on investment but for comfort and livability in a tight house. How are you planning on ventilating the place? In our area if you used flex duct in a basement you would be laughed out of town. We use all sheetmetal, no duct board or flex. The chase is nice but way overkill, just have the clowns install a duct with two return air outlets on it if you don't want to use the chase unlined. Only about 15 minutes of work to install it once you make it up.
    "Go big or Go Home"

  11. #50
    Join Date
    Jun 2001
    Location
    DFW
    Posts
    684
    I have manual D and used it to design the duct work that I installed. I also have and have run HVAC calc on my house to calculate the necessary cooling and heating requirements.

    The only flex duct work was installed by the HVAC contractor between the air handler and the ends of my sheet metal duct work. I knew I was going to be stuck with that, so I sized my work accordingly. The sheet metal supply ducts in my house are sufficient for about 1,800 cfm. So even with the flex duct connections, the total static pressure is going to be quite low.

    I have run HVAC calc many, many times with different estimates on infiltration, etc.. So, I have a pretty good idea what areas of the house are important for me to spend my time and money on. According to HVAC, the total cooling load on my house is 16,137 BTUH.

    There is a 6" fresh air intake into the return air of the central system for fresh air.

    In a cooling dominated climate, it is preferable to place all of the supply and return vents up high. In 99.9% of the houses in this part of the country, that is through flex ducts in the attic with ceiling registers.

    While waiting for the rain to stop so the foundation could be poured, I spent many hours in my shop building wall stacks so that all of the supply vents could be placed high up on the walls.

    In a more northern climate, the ERV would make more of a difference in comfort than it does in North Texas. Different climates lead to different answers.

    I prefer sheet metal duct work. But if I specified sheet metal duct work instead of flex, I would have to search long and hard for a contractor that was capable of doing the work, and the cost would be at least triple. So, lots of DIY.

  12. #51
    Join Date
    Dec 2006
    Location
    Arkansas
    Posts
    292
    Quote Originally Posted by paul42 View Post
    In a more northern climate, the ERV would make more of a difference in comfort than it does in North Texas. Different climates lead to different answers.
    I am not debating your choice to not use an ERV, but in northern climates an HRV is a more likely choice. I believe the ERV was developed for the warmer climates to provide fresh air and recover the energy.

    The concept is right on although the economics typically don't work. Maybe the ERV costs will come down to the point they will be worth installing.

  13. #52
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    Aug 2003
    Location
    Fort Worth, TX
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    Quote Originally Posted by paul42 View Post
    The only flex duct work was installed by the HVAC contractor between the air handler and the ends of my sheet metal duct work. I knew I was going to be stuck with that, so I sized my work accordingly. The sheet metal supply ducts in my house are sufficient for about 1,800 cfm. So even with the flex duct connections, the total static pressure is going to be quite low.
    How low? Do you have a number arising from your calculations?

    Ductwork capable of flowing 1,800 cfm is pretty generous for a two ton system that needs only 800 cfm. If you sized each supply outlet using a friction rate for 1,800 cfm vs. 800, you're likely to have insufficient throw and way too much drop at each supply register. Although each supply outlet will probably be whisper quiet, it will dribble cold air out into the room and generate cold draft complaints for occupants near the outlet. Other areas of the room may become too warm and stuffy.

    Another concern...if your duct system static is too low (a rarity, yes, but might be possible in your case), your indoor blower might actually move more air than desired...say closer to 500 cfm per ton vs. 400. For an arid climate like Arizona, 500 cfm per ton would net more sensible heat removal capacity, but we live in a mixed humid climate here in North Texas. Higher latent capacities come with lower cfm per ton rates...350-400 cfm per ton is about right for this area...but knowing the sensible heat ratio for the structure, derived from the Manual J calc, and designing the system around that factor is more desirable than a rule of thumb cfm per ton number, IMO.

    Lowering static pressure on a blower will cause the blower motor to become more loaded. If the static pressure is phenomenomally low, the motor may continuously run higher than its rated or running load amperage, shortening motor life significantly. Sometimes, less is NOT more...i.e. if bigger ducts means lower static pressure, then even BIGGER ducts would mean even lower static pressure and better system performance...right? Not necessarily!

    I have run HVAC calc many, many times with different estimates on infiltration, etc.. So, I have a pretty good idea what areas of the house are important for me to spend my time and money on. According to HVAC, the total cooling load on my house is 16,137 BTUH.

    There is a 6" fresh air intake into the return air of the central system for fresh air.
    Did you account for the additional sensible and latent load a 6" fresh air intake will impose on the cooling coil when you did your equipment size selection? Did you also derate the system nominal tonnage for your operating conditions, which are outside of ARI nominal tonnage ratings?

    In a cooling dominated climate, it is preferable to place all of the supply and return vents up high. In 99.9% of the houses in this part of the country, that is through flex ducts in the attic with ceiling registers.
    If 99% of the attics in North Texas had insulated roof decks or radiant barrier equipped roof decks, attic mounted ductwork would not be the sticky issue it now is.

    While waiting for the rain to stop so the foundation could be poured, I spent many hours in my shop building wall stacks so that all of the supply vents could be placed high up on the walls.
    High sidewall outlets are actually not as preferable in a cooling climate such as North Texas vs. ceiling diffusers/registers. While 99% of local residential installations use attic mounted ductwork with ceiling supply registers, almost none use round ceiling diffusers, which is almost ideal for a cooling climate. I now own a house with round ceiling diffusers...it's 48 years old. Those old dead a/c guys knew a few things about air distribution us younger contemporary counterparts could stand to relearn.

    In a more northern climate, the ERV would make more of a difference in comfort than it does in North Texas. Different climates lead to different answers.
    Actually, ERV's are for more humid cooling climates, vs. the HRV which is for heating climates.

    I prefer sheet metal duct work. But if I specified sheet metal duct work instead of flex, I would have to search long and hard for a contractor that was capable of doing the work, and the cost would be at least triple. So, lots of DIY.
    DIY that can lead to problems due to lack of experience and information. As for contractors that can run sheetmetal vs. flex...I can name some off the top of my head...R & D Sheetmetal, for starters. A strictly residential contractor won't bother with sheetmetal because commonly speaking all he knows is how to fling flex around like octopus tentacles. You want a good sheetmetal job, hire a commercial HVAC contractor or sheetmetal firm like R & D. You'll pay a bit more, but you'll get commercial grade work.

    Of course that's probably water under the bridge for you, seeing you've already made up your own ductwork. Being that I can't see your system from here, I may be speaking out of turn regarding its sizing, but if you sized it for 1800 cfm like I think you may have, you may be in for some performance problems down the road.

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