If it quacks like a duct...?

[dallasbill]

OK... I am starting a new thread because I want to post some pics (at bottom) specifically related to my HVAC sub's ductwork so far (you are welcome 41gasman!) He has rectified a lot, but there is still some stuff I am not pleased with. I base this on reading here, and on Internet research on good flex duct design/install.

I'd like to ask comments on the pics because I am going to get them fixed. The sagging is easily bad, but others may be open to argument. Esp. if I am a consumer -- via my GC who is onboard w/ this -- telling an "HVAC pro" it needs re-work.

Specific concerns:
1) duct passing over duct in subfloor cavities -- he may say that only the outside R6 insulation layer is crushed, not the inner air-bearing layer.
True? ..or comments I can counter with would be appreciated.

2) In many, many places -- and I have no pics here -- instead of using a 3-seam elbow to feed a vertical-boot outlet, they have used mitred floor-boot outlets instead. I have read that this sharp right-angle on the inside turn of the mitred boot causes CFM turbulence at the exit and adds an eqiv. length 40 feet longer than the other way. I want them removed and replaced with 90-corners and vert. boot outlets. Comments?

(See this Home energy Magazine article for that info I used):
http://hem.dis.anl.gov/eehem/01/010314.html

As I have posted before, this is an energy efficient ICF home. We are not going to cut corners and the HVAC guy says he will do what he needs to do to make us happy. That is very good! So, I want to be informed and fair when I bring these points up.

As always, your professional comments are appreciated!
:-)

http://pg.photos.yahoo.com/ph/cloare....net/my_photos

[docholiday]

Well it could be cleaned up a bit for looks. Certainly not the way I wouldve done it.

Ok now... and I am asking because I aint no builder.. but isnt there some limit to the size of hole you can cut into one of those engineered joists?

[Toolpusher]

My thoughts too Doc,

If the floor sags, will he sue the duct Mfg for not holding up the floor ?

[trane]

Originally posted by docholiday
Well it could be cleaned up a bit for looks. Certainly not the way I wouldve done it.

Ok now... and I am asking because I aint no builder.. but isnt there some limit to the size of hole you can cut into one of those engineered joists?

The ducts are the least of your problems. You need to have your builder check into the holes in these joists. They are very specific on what can be done and this cannot be done.

[oloenneker]

As far as i can remember, you can cut a hole up to 2/3 the size of the TGI joist as long as you do not cut the top or bottom of the "I Beam" part. But I do agree, that hole is much bigger than that. Suprised that the inspector did not sqauk a little on that. The ductwork looks messy, but functional.

[supremehvac]

I've seen worse, it's hard to tell with some of pics because I can't see more of the duct run. On the one he just needs another strap. On the one going up to the sub floor it looks like it is going into a register boot and dosn't seem that bad. The one that over laps the other is hard to tell from the pic if it is crushed bad enough so that it will cause a major problem. The Y fitting should be fine, but tough to say with out seeing more. As far as the holes I'm sure they are acceptable. I like to use all galv pipe on my jobs, it works and looks better. So this isn't the way I would have done it either. Make sure the flex is supported good at all the bends it will be likely to kink some over time.

[dallasbill]

All of these pics are from the first floor, looking up at the 2nd floor subfloor above the kitchen, pantry, downstairs bedroom and garage -- which has a media room above it. Space was limited due to design of home. You can see it all from Day-1 at http://billusa.********.com but it will take awhile.

I will check on the TGI joist hole issue -- it's news to me. The holes for the largest duct pass-thru's are well within 1" at the top and bottom where the beams are. I guess I need to do some more Googling to educate myself there too!

As to "crushed bad enough" where they pass over-under: there is about 1/2-3/4" compression on each outer surface of the R6 -- the duct surfaces that touch each other and then the top surface pressed against the bottom of the 2nd floor subfloor.

Could anyone please comment on my question #2?

Thanks!


[Edited by dallasbill on 02-07-2005 at 10:08 PM]

[trane]

Question #2- I use these 90 degree boots all the time with no problems. It seems to me that there are other problems that need your attention more. If you want a 90 elbow and straight boot at every register its going to be below the bottom of the floor truss and I don't think you will be able to tell any difference from one to the other.

[supremehvac]

If it is only compressed 1/2" - 3/4" then it's fine, what other option does he have for that duct run, I'm guessing none.

Can you post a picture of one of these mitered floor boots, I'm not clear on what you mean. Is it a 90 boot like mentioned or something the installer fabricated in a half ass way.

[Edited by supremehvac on 02-07-2005 at 10:24 PM]

[trane]

He means a boot that is usually called a 90 degree or angle boot which is used in all houses by most contractors because a straight boot and elbow will hang below the bottom of the floor joist.

[docholiday]

An angle boot or 90 degree boot is pretty much standard and I dont think thats a problem, a straight boot with a 90 may be too tall for the joist space between the ceiling and the floor.

The boot, by design flares out from the round to the rectangle. Its a non issue. I should add that you arent fussing about flex being run so why worry about something as trivial as an angle boot?

Overall the job looks acceptable if you're ok with flex runs where rigid pipe could easily have been run. The only thing I would question as mentioned is the holes in the joists.

[Edited by docholiday on 02-07-2005 at 10:28 PM]

[supremehvac]

Originally posted by trane
He means a boot that is usually called a 90 degree or angle boot which is used in all houses by most contractors because a straight boot and elbow will hang below the bottom of the floor joist.

I agree then I use them to.

[trane]

Doc, you must call them angle boots because I put 90 first and thats what I call them. Looks like we were thinking alike though.

[docholiday]

Actually we answered at the same time, you just hit the enter button first. (both at 10:25).

I should claify an ealier comment, Flex can be used effectively as long as the added friction is considered. Just remember turbulance is part of the friction and as far as I know, there is just about nothing worse than flex for turbulance. To clarify, I meant that the 90 inside corner of an angle boot is probably less that 0.5% of the friction in those runs and probably not more than the resistance of the grille itself leaving 99% of the friction as a result of using flex.

[docholiday]

Dallas, the 90 thing you may have read is primarily a trunk line thing.

If you have a rectangular duct and make a 90 degree turn and do not round the inside of the fitting, then rounding the outside of the fitting is virtually useless. What happens is the air along the inside of the turn maintains a straight heading and colides with the air being swept around the corner and basicly forms curtain of air that requires additional energy to overcome. By rounding the inside corner of a 90, you allow the air to flow more smoothly and evenly. The ideal 90 would have turning vanes installed.

But you are right in the sense that every fitting does have an equivelent length associated with it. I didnt look it up but for a single supply, I am not sure the differnece between a round 90 on a straight boot is equivlent to 40 feet less than a 90 boot. I'd almost bet the 90 boot isnt even worth that much to begin with.

[trane]

Angle boot= 30 ft. duct
Straight Boot= 5 Ft. duct plus 90 Degree elbow= 10 For a total of 15 So its half.

[dallasbill]

Thanks guys... you are great! I like a good discussion!

I won't worry about the angle boots! And the flex duct 'drag' itself was accounted for in design -- I'm just making sure that I get other opinions.

As others have stated "I woundn't do it thay way, but it looks OK from here" ...that's what I am looking for... reasoned opinions from others... and I thank you all~!

In the end, I can live with stuff IF I KNOW what other pros do or don't do.

And I will ask about the holes -- I think they probably look worse in a photo than they are and my GC is A-1 on not letting anything like that slip by if it will compromise this house quality. I walked through 3 other houses (not his) near here this past Sat. and they all have them in the 2nd floor subfloor for these large duct runs. Must be a Dallas thing.