Hello,
Depending on the geographic area, different opinions about design prevail. In the south, where AC really needs to be right, what you call spider, is the typical system. Either flex or metal duct. The trunk design system is only used in commercial applications or very large buildings.

Depending on the room size, 2 6-inch ducts might be enough. 2- 6 inch approximates 1-8 inch. The 10 inch is 50% more area than 2-6 inch ducts. If the ducts were originally installed for heat only, they are probably undersized for HVAC. If HVAC whisles at the grille, the duct and grille is undersized. Undersized systems fail prematurly and require more service. Square duct is very expensive. See what local code allows. Get more bids.

Thanks Bob. I'm kind of almost giving up on this. I don't know who to trust and I'm tired of making time for people coming to look.
I thought 8 contractors would be enough.

You are correct about the South!! I had a friend who did CAC systems and ordered all this stuff for my home when it was refurnished about 4 years ago from Florida (I'm in NY)! Well, he didn't really know what he was doing and now I'm trying to get it resolved and I haven't spoke to him in the 4 years! lol
Every supply to to every room is 6'!!

The room size with the 2, 6" ducts is 180sq ft. But this room is furthest from the air handler and is a loaded with 5 windows, 5 ft door and huge skylight.

So I guess the other guy was correct on the 2, "6 equaling 1, 8".
This was the guy that I'm hoping calls back. He came in and really knew his stuff. This was over a week and half ago that he came, but I'm hoping he calls back. Basically an entire overhaul of all the duct work and new trunk and spin the AH around to fit the trunk..... etc... Like a new install.

Time will tell.

hello,
2 6in ducts of flex are good for about 390 sqft. It round metal about 200 sqft. This is rule of thumb by Carrier? many years ago. Flex can handle more air without noise. 8 in metal should be good for 210 sqft. Flex is good for 420 sqft. A 10 inch metal 390 sqft. 10 in flex 750 sqft.

Windows add to the btu demand. East and west facing windows the worst. A manual J would clarify this for you. Rule of thumb, if no major work is done between first installation of equipment and replacement and the house cools adequately on a hot day, replace with same size. A man J will give a ballpark estimate only. If the equipment only lasted for 4 years? there is a problem.

Yea, theres definitely a problem.
So the 2, 6" ducts for that room seem plenty. I wonder why the only guy that gave me a good vibe on what he knew said that 1, 10" would be needed. All the supplies are 6" in the entire house which people say is a no-no.
I don't know. I don't know who to believe. Now I'm aiming towards having the other guy come out who said the duct work is fine, though it needs to be balanced and some other work.

The A/C worked fine the 1st year but ran most of the day. Last year, it barely worked!!

Oh well, this will be my last shot at trying to repair this and if it doesn't work, wall units will be installed.

Thanks!
-Chip

I work for a reputable hvac co in Georgia. We do residential jobs anywhere from $2,000 to $50,000. We advise strongly against spider systems, ductboard systems, and all-flex systems. We typically run 10 and 12 inch galvanized pipe trunk lines and 8 and 6 inch branches, with some flex at the boot to reduce noise. Most of our residential business is retrofit, so we have seen all kinds of installations and the problems that resulted. Regardless of the numbers and consequent performance predictions, the bottom line is How much air comes out the register. Bear in mind that metal pipe systems require more labor, but there is a reason for this. Most contractors who cut costs do so by using flex and installing it quickly and improperly. Some use ductboard and do a good job, but it releases fiberglass particles into the air. Many of our competitors brag that their two-man crews can change out two systems in a day. We can't do that. We can do some systems in a day, but most require two, and of course some take longer.

The longer the pipe, the more friction, the less air flow. When we divide the air flow from a pipe into two smaller pipes, the size of the step-down is usually 2 inches. We use a 45 degree wye to split the stream. To split a 9 inch pipe, e.g., we typically use a 9x7x7 wye. Many of our competitors do not use 9 inch or 7 inch pipe because they don't take the time to size a room properly and they don't want to carry the extra stock.

One of the reoccuring problems that is found with duct systems is high static pressure. If the duct is designed properly, this will probably happen anyway. Todays higher SEER equipment must have larger than normal duct to obtain the SEER efficiency ratings. This means the ducts need to be oversized from what is optimal design. Flex allows more air before becoming noisy. almost double the air flow. The objection is the life span of the flex is not as good as metal duct. Many million dollar homes in Texas use flex duct.

While I do not agree with what SEER represents to the HO, I can read the results and see the higher SEER equipment needs a different design model to succeed in hot climates. When the air flow is reduced, the cooling capacity reduces. If a house is sized for maximum airflow, then the system will be inadequate for a hot climate. Furthermore the practice of extended operation time decreases the SEER by multiple points on the days over 86 degrees.

Thanks for all your replies.
Though some of the info you've provided sounds Chinese to me (Im Italian lol) I'm trying to understand.
Heres the strange part. Most of the people that came out said the air flow coming out of the vents is fine, except for the rear room which I barely feel anything (its also the furthest from the AH).
The guy that gave me the price said that he could balance the system to get more air flow our of the rear room.
He also said if the air is coming out but its not cold, then there something else that needs a tune up or repair or something.
Now just to let you all know, I had MANY people come out, who removed freon, added freon, changed a part, put a new small copper line from AH to condenser.....etc..etc. They all say if the air flow is there, it should be fine.
Ive spent soooo much $$$$ that this is my last resort.

Airsome, Ive heard the same from people that the spider system is not recommended...!

Gonna be another hot year.... lol

Ok. True, the existing system can be repaired and improved. Go for it. If the man knows what he is doing, you should be fine. Just don't pay up front. He should have absolutely no problem with that. Get the quote. Put it in writing. Pay nothing until the job is done and you are satisfied. This is how we do all our business, and it is only fair.

I assumed you were talking about the knowledgable man referred to Fri at 13:52. Rework, flip system. If he does the job to your satisfaction, you will be very happy.

HI Airsome,
Would you like to jump on the next flight to NY? lol :-)

The guy that your talking about never got back to me!

The guy that says everything will work as is, is the one Im describing.
For $1500, he will add dampers to all the supply ducts on the triangles (See the diagram above), balance the system and remove one of the 12" ducts that supply one of the triangles and install sheet metal tube to it so it can minimize the friction as this is the one going to the rear room.

Im not totally crazy on what he wants to do that it will work.
The only thing good about this guy is that I told him that I want to reinstall EVERYTHING, and he said I wouldn't have to and do it his way and save money.
I mean he could of said yea, reinstall everything and ripped me off, but he didn't.....
But Im not crazy about the system... I don't know...

That's how I picked my HVAC company.
I asked for a new system and they said:
"Don't do it. When this one needs repaired
then call us back.' And I did, very glad too.

HTH
Chris

Truth be told, that was what I meant at first, then I second-guessed your intention. Try it, you might like it.

This is a slight threadjack for a question to airsome in regards to ductboard.

I recently decided to redo my own ductwork using ductboard for the trunks after having a manual j & d performed. The original contractors used a 'one-size-fits-all' approach rather than sizing the ductwork for the needed airflow.

My question is this: Before choosing ductboard for the material, I tried to do as much research as I could, and ran across mentions of this fiberglass particle issue. Now, here is the problem. I have read stories of people with severe respiratory and allergic issues that resulted from fiberglass being blown into their home from a damaged duct surrounded by fiberglass.
However, I have yet to read or find any evidence (even anecdotal) that ductboard causes a similar problem by itself.

I have, however, run across well-documented tests performed by many that indicate that there is no significant addition of fiberglass from ductboard, even at conditions well exceeding design specs.
For example,
Peter F. Hays (1991)
Detection of Airstream Fibers in Fibrous Glass Duct Board Systems
Indoor Air 1 (4), 522Â530.
doi:10.1111/j.1600-0668.1991.00016.x

Now, admittedly, I am assuming that these studies were funded by the ductboard manufacturers. However, I haven't seen any hard evidence whatsoever from the opposing camp.

For my own peace of mind, since I am still at a point where I could rip out the ductboard if need be, can you provide any supporting evidence for your claim that ductboard releases fiberglass particles into the airstream?

Thanks

No I can't. However, we (I and the company I work for) have personal experience with ductboard. When we physically pick up a sheet of ductboard we immediately become covered by a cascade of fiberglass particles which infiltrate our clothing and our skin and make us totally miserable for the rest of the day!
Other problems: If there is a mold issue in the house, it will become readily apparent when the interior surface of the ductboard is inspected. There will be large patches of black coloration in the top layers. But nobody looks for mold on the inside of ductwork until it is indicated by other symptoms.
If there are air leaks in the ductboard, or similarly, if there are air leaks around ceiling penetrations to your attic, they may be visibly indicated by a mottled black streaking effect near the air gap, as the fiberglass acts as filter.
"OH NO! I HAVE MOLD!" says the homeowner. "What's a mother to do?" (from an old TV commercial). :-)
Well, what is a reputable hvac contractor to do? Keep using ductboard? Why?
Over a period of several years, especially if the contractor takes shortcuts in the forming of the duct (for example, using a "V" cutter instead of a shiplap (more expensive)), the structure of the ductboard will deteriorate, thus increasing the likelihood of above problems.
On the other hand, there have been improvements in the manufacture of ductboard in the last two years or so. Chemicals have been added to seal the top layer so that fewer particles are picked up by the airstream. But I have yet to see the benefits of such advertised methods.

Thank you for your response. I've also had the miserable experience after working on ductboard for a day -- but as long as that's the extent of it, I don't mind so much.

As far as the mold is concerned, in your experience, is ductboard more likely to grow mold than any other type of ductwork? It seems like mold will grow on any surface (concrete, steel, tin, fiberglass) given moisture and food (dust, etc).

Also, I have been using shiplap tools for my ductwork, but it is more because that was what I could find ($120 on ebay for a used set in good condition) than because I was aware that shiplapping is inherently better than v-grooving. Out of curiosity, what is it about v-grooving that makes an installation more likely to deteriorate?

I do expect that there will be some debris being blown into the house for the first hour or two that the ducts are used after installation, and had planned on using filters at the registers for those few hours to make sure nothing unwanted blew into the home.

One thing that I really have enjoyed about the ductboard is that it has made it possible (even easy) for me to do this work myself. One thing I have found -- you just can't pay someone else enough to care about your home the way you will. I know there are good contractors out there that do good work (although they seem to be few and far between), but still, at the end of the day, it's a home to me, and a job to them.

Thank you again for your time to respond.

Posted by kodiak_jp on Thu, Feb 22, 07 at 1:28...

"One thing I have found -- you just can't pay someone else enough to care about your home the way you will."

That's one of the reasons why I replaced my furnace, oil tank, metal ductwork, and flue pipes myself. The other reason was cost.

The original ductwork was a catastrophe installed by a pro. There's no way he would settle for such poor planning and excecution in his own home. Maybe he just didn't give a darn.

Either that, or the original homeowner was a real cheapskate who demanded a rock-bottom price. Time is money. The installer won't spend one if the customer won't spend the other. From the lack of upgrades to the home - and some of the DIY work - this scenario is not beyond question.

Peace.

Marco

Well, I'm ready to almost throw in a towel!
The guy that I liked best came back to re-evaluate everything and he said I simply don't have enough room to install a trunk line!
Now I'm basically left with few options:
1. Go with the guy that wants to balance everything, add dampers...etc...but I'm still not comfortable with this system.
2. Call another gazillion contractors in
3. Have an AC guy evacuate the system and I will attempt to do everything myself (Ive been pondering this idea).
4. In the wall AC units (burns a hole in my arse to do this as I removed the ones that were there when the house was remodeled!! lol)
If I do it myself, I would need to remove the air handler, remove all the spider duct system. Then spin the AH around and see how big of a trunk I can put on and attach all the ducts.
Im very handy, but I simply dont have the time!!! ARRGGhhhhh

Sounds to me like nobody wants to work on your house. There must be some real disadvantages there, not conducive to the contractor. If so, what do you think these disadvantages might be? How small is the space? How can there be enough room for a spider system but not a trunk line? If you think these issues are relatively unimportant, who have you been calling? How did you select them?

I have a wideline cape. There is no attic in the house. The only space available is behind the walls on the second floor.
There are 2 doggy dormers for the windows in the front, so it restricts the amount of room. I beleive it can be done and it is tight, its just that no one wants to do anything tedious.

The rear of the house theres a small dormer in the middle for the bathroom and both sides of the house have about 15ft on each side. Yea, should have been installed there since theres so much more room.
The current trunk on the system is only 16" long and then has 2, 12" ducts that feed the triangles. The spider system barely fits.
But if the unit is turned around and moved toward the front of the house, the trunk can extend of the ceiling over the staircase.

Some of these people have been referred to me and others were out of the yellow pages.

Out of fairness, 1 guy just called me back about an hour ago and said he will give me a price tomorrow on doing this.
I hope I don't fall off my chair with the price....

You definitely will have to find the just right contractor.
If you try to do this job yourself, you will be miserable.
Take your time. Your patience will reward you.

We have done a few similar jobs here in Georgia. The ones that come to mind took a week or so. One of them wanted the job permitted. This made life a little more difficult for us, but we were happy to comply. If you doubt your contractor, permitting can be a good way to protect yourself.

Yea, I agree I just have to find the correct contractor. Haven't had luck yet.
What do you mean by "permitting"? Is that a guarantee of some sort or getting a permit from the town?

Basically, it is a building permit. You go to the planning commission or similar body, get the permit, post it outside, on your house or a sign. After each step of the installation, a building inspector must approve it before the next step can proceed. He will indicate his approval on the permit. Many contractors will balk at this, and you could conceiveably lose a good one. So you may not want to insist on it, just ask if he thinks you should get one.

@chippy - its been a while, but what was the end result? we’re having a similar issue.