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  1. #40
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    Jun 2014
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    Dover, DE
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    Rough estimates of increased airflow with each size.
    That’s if your current duct is ideal and flows around 1,700 CFM. Which I’d guess does not with all those twists and bends.

    10” ~300
    12” ~480

    You need around 350-400 CFM per ton of capacity.
    I havent failed. Ive just found 10,000 ways that wont work. - Thomas Edison

    Its not whether you get knocked down, its whether you get up. - Vince Lombardi

    "In this house we obey the laws of thermodynamics" - Homer Simpson

    Local 486 Instructor & Service Technician

  2. #41
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    Nov 2019
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    Quote Originally Posted by rider77 View Post
    Rough estimates of increased airflow with each size.
    Thats if your current duct is ideal and flows around 1,700 CFM. Which Id guess does not with all those twists and bends.

    10 ~300
    12 ~480

    You need around 350-400 CFM per ton of capacity.
    Yeah I wasn't a big fan of just patching them with a small addon so I think that's kind of off the table. I think the market in this town kind of makes all the contractors just naturally veer towards the cheapest, duct-tape style solution to everything so that's where it always starts.

    The only quote they are coming up with is for the custom box. We were also debating whether it was worth moving the second ceiling grille over to be right next to the first one, so it would be more of a straight shot into the unit. On the one hand it would be easier for the duct work, but on the other hand it would mean moving the return supply for the downstairs unit 4 feet farther away from the open spiral staircase that it sits kind of kitty corner/above right now.

    Here is a picture taken from the downstairs in the middle of the stairwell, you can see both ceiling grilles.

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  3. #42
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    Jun 2014
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    Dover, DE
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    Since they are set on only using a central return, hopefully the carpenter undercut the doors so the system could at least halfway function while running.
    I havent failed. Ive just found 10,000 ways that wont work. - Thomas Edison

    Its not whether you get knocked down, its whether you get up. - Vince Lombardi

    "In this house we obey the laws of thermodynamics" - Homer Simpson

    Local 486 Instructor & Service Technician

  4. #43
    Join Date
    Aug 2002
    Location
    Southold, NY
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    Without a base Line reading how do they know what size ducts to add? They dont!

  5. #44
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    Nov 2019
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    Quote Originally Posted by rider77 View Post
    Since they are set on only using a central return, hopefully the carpenter undercut the doors so the system could at least halfway function while running.
    Yeah, the doors are undercut. I've actually thought about just planing off another 1/4 inch or so to help a little bit heh.

    We also talked about adding more returns elsewhere, but they seemed in a hurry and just said they would do the quote for the boxes and we could talk about other returns later. The problem with adding returns is that it only helps with the supply issue for the upstairs unit, I can't pull any new ductwork to the first floor and there are no returns on the first floor at all right now. So we kind of kept it focused on the central returns for now since that helps BOTH systems, and then upstairs where stuff is actually accessible we'll probably also add some additional stuff too.

    I got the impression that they thought their quote would scare me off and they were wasting their time, so I'm curious to see what they come up with. I'm kind of expecting it to be like $-$ to fix everything, so hopefully whatever they come up with won't actually scare me off heh


    Quote Originally Posted by pecmsg View Post
    Without a base Lin’s reading how do they know what size ducts to add? They don’t!
    I dunno, the guy didn't even have his phone app duct size calculator because he just got a new phone. I'm not exaggerating when I say this town is just stupid. The first HVAC company I called was this one:

    http://www.airsupplyinclv.com/servic...ation-service/

    They said they no longer do duct work because their duct work guy moved to California.
    Last edited by beenthere; 12-03-2019 at 06:22 AM.

  6. #45
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    Aug 2002
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    Southold, NY
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    Quote Originally Posted by Droo View Post
    Yeah, the doors are undercut. I've actually thought about just planing off another 1/4 inch or so to help a little bit heh.

    We also talked about adding more returns elsewhere, but they seemed in a hurry and just said they would do the quote for the boxes and we could talk about other returns later. The problem with adding returns is that it only helps with the supply issue for the upstairs unit, I can't pull any new ductwork to the first floor and there are no returns on the first floor at all right now. So we kind of kept it focused on the central returns for now since that helps BOTH systems, and then upstairs where stuff is actually accessible we'll probably also add some additional stuff too.

    I got the impression that they thought their quote would scare me off and they were wasting their time, so I'm curious to see what they come up with. I'm kind of expecting it to be like $1500-$2000 to fix everything, so hopefully whatever they come up with won't actually scare me off heh




    I dunno, the guy didn't even have his phone app duct size calculator because he just got a new phone. I'm not exaggerating when I say this town is just stupid. The first HVAC company I called was this one:

    http://www.airsupplyinclv.com/servic...ation-service/

    They said they no longer do duct work because their duct work guy moved to California.
    Its not just your town. Only a small % of contractors want to do it right. Keep looking there out there!

  7. #46
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    Aug 2002
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    If they are not testing, they are guessing and hoping for the best.

    A simple static test takes very little time, but you could offer to pay for such a test to see if they truely know even how to do it. Take pictures of where they test it and what the readings are. On your equipment there should be 3 small hole locations. One hole right before the blower at the furnace for the return static, one right after the furnace but before the evaporator coil for the supply static, and one right after the evaporator coil for the supply duct static.

    This test will show where your issues are and it is simple to do.

  8. #47
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    Nov 2019
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    Quote Originally Posted by Advanced Response View Post
    If they are not testing, they are guessing and hoping for the best.

    A simple static test takes very little time, but you could offer to pay for such a test to see if they truely know even how to do it. Take pictures of where they test it and what the readings are. On your equipment there should be 3 small hole locations. One hole right before the blower at the furnace for the return static, one right after the furnace but before the evaporator coil for the supply static, and one right after the evaporator coil for the supply duct static.

    This test will show where your issues are and it is simple to do.
    They (there were actually 2 guys together) said they would have to send their "air quality" team over, and they would drill a series of holes on the supply side in the box before the blower. They would take a measurement through each of these new holes and average them out to get static pressure. Your way sounds a whole lot easier and makes more sense to me!

    They also suggested cutting a 10" hole in the box in the attic and duct taping a cheap air filter over it, to see if the noise was effected enough for me to go ahead with the modifications. I am still getting at least two more quotes so I didn't want to do that just yet.

  9. #48
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    Apr 2011
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    SE Washington
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    cheap stamped return grills, take and straighten out the louvers on the grills and see what pitch changes, agree 20" not enugh, but louvers are cheap fix for annoying grill noise

  10. #49
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    Yeh box you are referring to is called the return box(meaning returning house air to the furnace).

    The supply box and ductwork is after the furnace and is what supplies your home with conditioned air from the furnace.

    Drilling several holes and taking an average reading, sounds like they are talking about doing a transverse cfm or velocity measurement. Which is different than a static pressure measurement.

  11. #50
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    Nov 2019
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    Quote Originally Posted by Advanced Response View Post
    Yeh box you are referring to is called the return box(meaning returning house air to the furnace).

    The supply box and ductwork is after the furnace and is what supplies your home with conditioned air from the furnace.

    Drilling several holes and taking an average reading, sounds like they are talking about doing a transverse cfm or velocity measurement. Which is different than a static pressure measurement.
    Yes, he mentioned measuring velocity of the air during this test so you must be right. I was very clear about a static pressure test, I used that phrase about 5 times and I showed them the table from my blower manual of CFM per fan speed setting at different static pressures, saying "I'd really like to know where the systems are at right now on this table, because I think the goal is to get it to 0.5 or less".

    My wife says the first person who can successfully measure static pressure gets the job. I wonder how many people it will take to find one!

  12. #51
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    Jun 2003
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    Texas
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    if ya open all the filter grilles does it still have the noise?

  13. #52
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    Nov 2019
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    Quote Originally Posted by poppa View Post
    if ya open all the filter grilles does it still have the noise?
    Yes, the noise is still there without any filters. I think it's just the amount of air being sucked through the single 20" round duct - the noise in the attic right next to the unit is actually really good so it's not a weird vibration thing.

    First quote came in at $ to fabricate and install two custom boxes replacing the 20" flex and existing ceiling box. Pretty much what I was expecting, but these guys don't seem that good and have been trying hard to sell me on a UV light which I definitely don't want or need. Two more companies coming tomorrow, they both seemed pretty good on the phone so with any luck I might finally get that pressure test done tomorrow
    Last edited by beenthere; 12-03-2019 at 06:20 AM.

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