G-90 Ducting Cost Info?

[CuriouslyGeorge]

Is anyone familiar with G-90 ducting? It is a (special?) material used for outdoor ducts designed to withstand the elements. Also,I believe it has extra-thick walls for strength and/or to better guard against leakage.

I need pricing information (materials, labor, O&P) to install rectangular G-90 ducts, OR! I have RSMeans data on typical galvanized steel prices per lb. Can you give me a feel for a %mark-up for G-90 material, labor, etc?

FYI: My ducts (two different designs) will be 12x10 and 28x28, (width x depth) and let's assume 100 ft each. I'll just scale it from there.

Whatever you can provide would be greatly appreciated. Please specify if you're quoting bare costs or if it includes O&M. Thanks! - CuriouslyGeorge...sweatin' it!

 

[CuriouslyGeorge]

OK...what about double-walled duct, if nothing else?
- Curiously George

 

[CountOlaf]

I feel like we're designing whatever is you're working on. Why don't you send us all the drawings so we can check them.

 

[CountOlaf]

Alright, here goes:

The 2000 ASHRAE HANDBOOK—HVAC Systems and Equipment recommends ASTM A 653/A 653M, G90 (Z275) coating designation. The Sheet Metal and Air Conditioning Contractors' National Association's (SMACNA) HVAC Systems—Duct Design states that the G60 (Z180) coating designation is adequate for most applications. The "G" number is the total weight of zinc coating on both sides of the sheet in hundredths of an ounce (gram). Lock-forming quality is necessary to allow 180-degree bends without the metal or coating cracking and flaking on the outside of the bend.

Coatings protect materials from atmospheric corrosion. Corrosion resistance is a direct function of coating weight. SMACNA's HVAC Systems—Duct Design explains that the G60 (Z180) coating designation is suitable for applications where the duct is not exposed to industrial pollutants, marine atmospheres, or continuous contact with moisture. The 2000 ASHRAE HANDBOOK—HVAC Systems and Equipment, Ch. 16, "Duct Construction," recommends the G90 (Z275) coating designation.

In other words, G90 is practically the standard galvanized sheet metal you're getting from Means anyway. I doubt there's a signifciant "adder". Specify G90 for all your ductwork (unless your going with something special like SS, aluminum, PVC, etc.) Don't use it outdoors without some additional protection, even if that's only paint, as it will start to rust.

 

[imok2]

George, I hope this job turns out to be a big success as I feel you have a lot of us involved in it(smile) anyway
SMACNA has issued a free technical paper addressing zinc coatings used on galvanized steel ducts.

The paper refers to “Hvac Duct Construction Standards – Metal and Flexible,” second edition 1995. The paper reviews zinc coating thickness variations, as commonly used in trade practice. Also included are “the burdensome effects of imposing a universal requirement of G-60 and/or G-90 coating for all components.”

The paper addresses rectangular, round and oval duct, and duct hangers. Under “factors to be considered” it states: “Where ductwork exposures do not involve wet and dry cycles, high humidity and chemically polluted environments, the traditionally used zinc coating amounts reviewed herein have provided satisfactory service life in hvac system service… The service life of both G-60 and G-90 zinc coatings in outdoor temperatures is relatively short; G-90 is a recommended minimum on exposed sheet and reinforcements when supplemental paint coatings are not specified. The cost increase for G-90 versus G-60 coated sheet is small but availability varies nationally.”

The document was prepared by SMACNA’s director of technical services John Stratton. It is available for downloading free of charge at

http://www.smacna.org

in the “technical services” section

 

[CuriouslyGeorge]

You all must work in the real world where you have access to all these references. I have squat, but I am expected to perform. My neck is on the line, and I've spent the past 18 months out of work. How you would feel in my shoes? I hope you guys sleep well at night because I sure don't. You think I'm asking these questions as a hobby?

I thought these boards were for professionals to share information. If I had those books...I wouldn't need this Board, would I? Do you really think everyone who works on HVAC starts off at the expert level?

Put yourself in my shoes! This is exactly why a good mentor is one in a million. All the time in the classroom (in Mech Eng, not HVAC per se) is such a waste when it has nothing to do with the real world. I'm so glad I sent all my money to college to learn squat...not Daddy's money, mind you, by MY money. I've busted my butt for everything I have in this world while (most) of you all don't even appreciate what life has handed you so easily...

So, when you go to church and humbly claim what a good soul you are, think about us earthworms who scorunge for every crumb you throw to us - C.George, pist!

 

[CountOlaf]

I don't go to church.

 

[cme]

G90 is standard commercial grade ductwork, .90 oz zinc/sf duct

G60 is residential, .60 oz/sf

G90 had 50% more corrosion resistance than G60 because of the greater zinc content

G115 is 1.15 oz/sf and is found in cooling towers

I use Means for the duct weight tables in the back and use $6.00/lb .... 3.50 matl + 2.50 install

Means is horrible for equipment cost, get quote from vendor

I calc only a few duct sizes; no smaller than 12x12

 

[CuriouslyGeorge]

Thanks, CME...your info is a great help. To all, sorry for ranting, but people quicky forget where they came from when they were cutting their teeth. In my case, it's more like cutting my throat! - C.George

 

[imok2]

George, If I offended you, it was not my intention. Im sure we understand where your coming from as probably most of us have also been there. Lighten up and try to accept the things you cannot change and change the things you can. As far as references are concerned it's taken me over 30 years of study and accumulation of resources, this is a life time profession. Between you and this board, I think an apology,
is in order

 

[cme]

let me correct myself .... G235 is used in cooling towers

 

[HVAC68]

Well, I'm probably not answering the question George has asked, but will reply to his "ranting".

imok2 is absolutely right. After 14 + years of experience in the industry, am still learning. I wish I knew about this forum earlier. The references that imok2 gives is amazing - I have always wondered how he's able to get out these links so quickly. I'm sure he has a great filing system only for links !!!

George - Cool down. Everybody goes through the same when they start their careers - I haven't heard of anybody who knew everything the day he/she started his/her career. I believe you are no exception to that. The link imok2 has given is a "free to download" link.

I just referred imok2 - but there are such great guys around like quark, lilliput1, friartuck, etc., to name a few that comes to my mind immediately.

Good luck George

HVAC68