Takeoff

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MITTS
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Takeoff

Postby MITTS » Sun Jan 31, 2016 5:38 pm

See any issues with a take off like this?

Wasn't sure why elongated takeoffs were still perpendicular.

I am looking to grab as much air as possible. Ran two 6" lines from the basement to the attic and dropped in two bedrooms that are cold/hot winter/summer

IMG_20160131_162408403_HDR.jpg


Saw another style that grabbed air with the damper door that might be better if this doesn't work.


Image
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Re: Takeoff

Postby CEO1 » Sun Jan 31, 2016 8:19 pm

Yeah, looks good to me...the one with the scoop would catch more air. I've rigged scoops on existing run outs a few times. ;)
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Re: Takeoff

Postby AC480 » Mon Feb 01, 2016 7:55 pm

That really looks good, it may work just fine.
When I built my house I ran a square metal trunk line the length of the house which reduced every so many drops. The first drops were going to the Master Bedroom. We weren't getting any air. Apparently the velocity was too high and the duct wasn't pressurizing. All the air was stacking up at the end of the trunk line and dumping through the last registers on the run. I was able to make some improvement by throttling the dampers, but I still wasn't getting what I needed in the MBR and bath. I must have messed up somewhere in the calculation of the size. I wound up getting some round start collars with scoops, which solved the problem. A picture of them is on the attached catalog page. If it doesn't divert enough air to suit you, I think if you add an adjustable scoop from the picture MITTS posted it would solve the problem. I like the looks of that design because it is adjustable. Are the runs in question some of the first drops off the trunk?
scoop and damper p10.pdf
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Re: Takeoff

Postby MITTS » Tue Feb 02, 2016 6:36 am

It will be the first two and it is in a tee section that feeds into the main trunk line so what you were saying might be an issue.

There were some videos MecAcc posted at ProTech that really stuck with me showing the air flow difference between a elongated takeoff and perpendicular ones. They showed some drasticly long mouthed ones that I just don't have room for but the difference in air flow shown in the video was dramatic.

Another from a different video he posted I might also try for a little extra return was to attach a straight piece of round to the inlet of the blower wheel. By straightening the flow of air entering the blower the fan was able to move more air.
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Re: Takeoff

Postby Rat » Tue Feb 02, 2016 1:05 pm

That may work, but it isn't the best option. The best option in this case would be a radiused shoe tap. I don't like extractors (the scoop) unless I am moving 50% of the air in the main trunk (like at a tee in the main); they cause too much turbulence and increase in static.

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Re: Takeoff

Postby MITTS » Tue Feb 02, 2016 1:51 pm

Thanks Rat but I Googled that and literally just got pictures of shoes lol
I don't got enough duct banger blood to know what that is ;)
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Re: Takeoff

Postby Rat » Wed Feb 03, 2016 2:22 pm

It's like a square tap or a square to round tap. Traditionally they are used for branching main ducts abut they really make a big difference for individual branch ducts as opposed to spin ins or just a straight tap. Looking at a fitting table the straight tap is worth 35 feet of friction while the straight shoe tap is worth only 10 and the radiused is worth 5; so you can cut down friction loss by 30 feet using them in a single branch duct.

When used as a main branch duct the fitter may also put in an extractor, which I don't use and is definitely not needed when using it as a branch duct tap in place of a start collar or spin in.

It is very similar to the elongated fitting you mentioned earlier. However, with the radius, the elongation doesn't need to be as exaggerated.

If you have a Shop Data fitting stencil it is fitting number F15 and is called a radius tap. It can be made as a square to square tap or square to round.

The radius in the below image is the key to good airflow; just like any other fitting.

radiused shoe tap.jpg
radiused shoe tap.jpg (13.07 KiB) Viewed 518 times


I think what you have will work. You may get some turbulence right there where it goes from flat to round; it would have been better to make that a true square to round transition. But I bet it will be better than what you had.

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Re: Takeoff

Postby MITTS » Wed Feb 03, 2016 2:45 pm

Thanks I'll try and make one with a radius and get a true transition from square to round. It might be too tight where I'm at to get the real thing unless I can find where to get a couple and they aren't too long overall.

Would you happen to know how long a 6" fitting is?
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Re: Takeoff

Postby MITTS » Sat Feb 06, 2016 8:14 am

Rat wrote:If you have a Shop Data fitting stencil it is fitting number F15 and is called a radius tap. It can be made as a square to square tap or square to round.

The radius in the below image is the key to good airflow; just like any other fitting.

radiused shoe tap.jpg




So I've been looking around and all I can find is the middle ground what they call a HETO or High Efficiency Take Off

I can see now why the slang term was shoe

Image

I happened to find this one too where they aren't using the perpendicular back on it.


Image

http://www.smcduct.com/sites/default/fi ... _11188.pdf



I realize now I think Rat was offering the radius as best but it is a special order shop made type of fitting and not on the shelf prefab???? I found the F15 reference pop up on a custom order sheet to have ductwork made up. I think the one I found it on listed as a F11 style.
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Re: Takeoff

Postby MITTS » Sat Feb 13, 2016 4:15 pm

Took two too many years putting this off so settled for the premade high efficiency take offs.

Most places around here didn't even know what I was talking about. This was a carryover project since protech since we moved into this house (cape cod)

The two 6" lines did it. I walked around with a beaded thermocouple and there is no more temp difference between upstairs and downstairs :)

It's 15° out now and before as soon as you would pass the ceiling height up the stairs from the first floor the temp difference would hit you in the face. Same difference in the summer and we used to run a window shaker.

Not anything to look at but its all I could think of with the cards delt.

Thanks for the help guys.

IMG_20160213_144610-640x511.jpg



Now I need one more line run which is for the upstairs bathroom.

Was going to run 4" but the piece of 3” sides up this chase so much easier. It's a 8x5x8 bathroom and we are taking out the window. Am I crazy thinking about 3" for this bathroom?
Our downstairs bathroom is so overpowered I have the damper and register both turned off and its the most over run room in the house. So figured 4" no problem but wondering about 3"
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