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Old 12-19-2011, 09:41 PM   #16
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inconsitent air flow


Doc, how much do you know about static pressure? If the register is closed the air still ain't moving through that run, which is what I assume you meant by cutting it off at the plenum with a damper....?

Explain to me the difference between shutting off a run at the register as opposed to at the plenum. Neither device is a 100% shut off, so let's ignore that.

Once the system pressurizes, the air is going to go somewhere. That 15' of 6" flex means exactly squat for volume, but that register at the other end makes all the difference in the world.

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Old 12-19-2011, 09:55 PM   #17
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inconsitent air flow


so make a suggestion on how to help his problem here without tearing his house/ductwork to pieces
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Old 12-20-2011, 09:33 AM   #18
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I never said there was an "easy button" option. Doing things right often requires a little effort, and it sounds to me like he needs to focus his efforts on modifying his ductwork.

It's kinda hard to get real specific since we don't know any specifics about his house or duct system.
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Old 12-20-2011, 09:38 AM   #19
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No it's not and again, closing off registers will have little to zero affect on esp. Closing off dampers at the plenum will have a huge impact.
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Old 12-20-2011, 02:03 PM   #20
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Explain the science behind that Doc. If the air ain't moving, it matters not if it stops at the damper or at the register. That run is still not moving air.

Do a little test. Go to your supply plenum and check your static. Then go close all your registers and check it again. If you don't record a difference your manometer doesn't work.
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Old 12-20-2011, 04:18 PM   #21
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The 2 main differences between using the damper at the register or at the supply take off. Is the possibility of noise. The damper at the register can give you noise as air pushes past it at the areas its not air tight at. Also, if you use the register damper, any section of that supply up to that damper that had air leakage before you closed it, will now have a slightly higher leakage rate. There is also a possibility that the supply run could develope leakage at joints that didn't leak before.
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Old 12-20-2011, 05:20 PM   #22
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Quote:
Originally Posted by brandonmcginnis View Post
Explain the science behind that Doc. If the air ain't moving, it matters not if it stops at the damper or at the register. That run is still not moving air.

Do a little test. Go to your supply plenum and check your static. Then go close all your registers and check it again. If you don't record a difference your manometer doesn't work.

i have two magnahelics and two brand new Fieldpiece digital manometers and I have tested this many times, beginning in schoOl last year with my instructor and a few dozen other people in the class right there and on job sites and at my own home. Not a noticeable change closing off registers.

I wouldn't have said it had I not already seen it with my own eyes, more than once.

Exactly what BT has said was the isuue, the exact same reason my instructor (of Goodman technical supPort and an hvac technician and business owner of 39 years) stated were the most probable causes. That and the diminishing value air has to length traveled.

Perhaps in a perfect world.
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Old 12-20-2011, 05:55 PM   #23
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I am not in any way advocating shutting off any registers. I've been against that from the beginning of this post! If there is balancing to be done, it should certainly be done with dampers at the plenum.

I am simply saying, that if you have X amount of airflow and a diminishing amount of discharge area, the static pressure is going up. The ductulator does not lie.
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Old 12-20-2011, 05:59 PM   #24
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I am not in any way advocating shutting off any registers. I've been against that from the beginning of this post! If there is balancing to be done, it should certainly be done with dampers at the plenum.

I am simply saying, that if you have X amount of airflow and a diminishing amount of discharge area, the static pressure is going up. The ductulator does not lie.

There's your problem, you're using a ductulator and not a manometer. Since the beginning of time engineering and actuality in this field have greatly differred.
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Old 12-20-2011, 09:42 PM   #25
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I have and use both. I'll stick with what has always worked for me.
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Old 12-20-2011, 10:02 PM   #26
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One has nothing to do with the other. A ductulator tells you friction rate and cfm (per duct size) and velocity and this and that but has nothing whatsover to do with wc concerning esp.

jEez dOod, did you go to schoOl, ever?
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Old 12-20-2011, 10:06 PM   #27
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I take that back, you have to have correct size ducts delivering the total system cfm or that's how you get into trouble concerning esp but still, you can't calculate esp from a ductulator.

That's what I should have said.

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