Takeoff

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Re: Takeoff

Postby CEO1 » Sat Feb 13, 2016 6:47 pm

I wouldn't have thought the 4" would work... :mrgreen: You' re on a roll with undersized piping, so maybe 3" will do enough. ;)
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Re: Takeoff

Postby MITTS » Sat Feb 13, 2016 7:31 pm

:lol:

It will be the first take off :mrgreen:

Since it will be way easier to run the 3 I'm just gonna do it and see
I'll use the 6" HETO and reduce as far down as possible.
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Re: Takeoff

Postby MITTS » Sun Feb 14, 2016 8:22 pm

If I'm doing it right I'm measuring about 50 cfm
It's gonna have to do
I don't think I'm getting a 4" pipe in there.

After a day of running and the bathroom still gutted it feels warmer upstairs than down stairs now so if need be I could always pull more air from a bedroom.

Turns out I didn't have much room to play with. It went right from the take off to two reducers then a elbow. Had to bend it over to make the drop spot.
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Re: Takeoff

Postby CEO1 » Sun Feb 14, 2016 9:57 pm

MITTS wrote:If I'm doing it right I'm measuring about 50 cfm


Down in this part of the country, for the A/C load, that's about right. And with mostly heat pumps, it works the same for heat.

Back when I did a few load calcs (early 1990's spec houses), they usually came out to 500-600 ft2 per ton, depending on windows and insulation. I never figured loads per room...just "eyeballed" the different sizes and added run-outs accordingly. For typical baths, I'd figure 50 cfm and run a 5" or 6" flex.

Going with the conservative 500 ft2 and 400 cfm per ton, you get 0.8 cfm per ft2. Your 5' X 8' needs 32 cfm...

Bullseye! You're batting 1000...
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Re: Takeoff

Postby MITTS » Sun Feb 14, 2016 10:23 pm

That would have never worked without that take off
It was moving some serious air when it was just that one 3" 90
Was like a hair dryer :mrgreen:
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Re: Takeoff

Postby CEO1 » Sun Feb 14, 2016 10:36 pm

MITTS wrote:That would have never worked without that take off
It was moving some serious air when it was just that one 3" 90
Was like a hair dryer :mrgreen:


Yeah, the take-off makes a difference. I've "fixed" lots of under aired rooms just by increasing the size of the take-off. :)
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Re: Takeoff

Postby AC480 » Mon Feb 15, 2016 12:16 pm

This has been an interesting topic. I haven't gotten very involved in ductwork, other than a simple pressurized residential plenum system. I am surprised how well the take-off worked. Does that "shoe tap" create an area of low pressure somewhat like the upper edge of an airplane wing and cause the air to turn into the tap?

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Re: Takeoff

Postby MITTS » Mon Feb 15, 2016 1:20 pm

I think they its described as
The Coandă effect
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Re: Takeoff

Postby AC480 » Mon Feb 15, 2016 1:53 pm

Thank you MITTS. Any particular reason why your pipe is not insulated? Is it in the conditioned space? No problems with condensation?
Choosing metal pipe was a wise choice. We usually use flex duct because it is easy. The problem with flex is it has a very high friction loss. Failure to properly stretch the flex prior to installation aggravates the friction loss. If you look at a friction loss chart for flex duct, it is going to show the best case.
Coanda effect is the phenomena in which a jet flow attaches itself to a nearby surface and remains attached even when the surface curves away from the initial jet direction. In free surroundings, a jet of fluid entrains and mixes with its surroundings as it flows away from a nozzle.
https://en.wikipedia.org/wiki/Coand%C4%83_effect

There is a lot of information on the Hart & Cooley website with charts and calculators including the XL air duct calculator:
Air Duct Calculator.xls
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Re: Takeoff

Postby MITTS » Mon Feb 15, 2016 2:32 pm

It's a work in progress ;)
We hired a company to finish the bathroom I gutted like two years ago and they started today so I was up last night insulating in the bathroom where I won't be able to get at. I'll be wrapping the rest or most of it later on.
I usually do everything but lately it's been tough getting time.
I was going to be working on the supply and return plenums because of the high static but too cold now. I shut it down again last note after everyone went to bed and figured no one would notice being under the covers but my youngest came up to see me dressed from head to toe in his snowsuit :lol:
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