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 Knewnews
Thinking XXX but only AA
 
Registered: 08/30/05
Posts: 1,809
Loc: desert floor
Last seen: 23 hours, 47 minutes
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 AC/Heating duct work = PVC? 
#16345884 - 06/07/12 01:30 PM (11 months, 11 days ago) |
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hey guys swapping out my AC unit, in the process i tore out my drop down ceiling (where the old flexy ducting is) to replace the old inefficient insulation.
i am doing most of the work besides the actual cleaning and hook up of the new FHU, condenser, and fan unit. my budget is about spent, i want to replace the flexy duct work with hanging exposed duct work (think modern loft kind of style). was thinking PVC would be a good way to cut expense while keeping things crisp and clean to the eye.
little confused, some says to only use underground/in cement slabs and others look similar to what i pulled out.
any advice with products or efficacy?
thanks
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ashfiken
TotalCrazyasshole
Registered: 09/06/06
Posts: 1,363
Loc: SChemestate
Last seen: 4 days, 23 hours
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Re: AC/Heating duct work = PVC? [Re: Knewnews]
#16345938 - 06/07/12 01:38 PM (11 months, 11 days ago) |
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I've just recently seen something similar to what you're speaking of mate... Being an amateur carpenter I noticed this at a certain house I was spending some time... The duct work uses PVC as components of duct work and works fantastically. I think it would be fine to use and cut costs and it also does have an aesthetically decent look...
hope this is relevant and helps.
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iateshaggy
i haxor 360s
Registered: 05/20/05
Posts: 4,281
Loc: 612 Warf Avenue, next to....
Last seen: 2 days, 4 hours
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Re: AC/Heating duct work = PVC? [Re: ashfiken]
#16347846 - 06/07/12 08:21 PM (11 months, 10 days ago) |
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i take it you are talking about a commercial application "drop-in ceiling". they do make solid duct "pipe" to run off of your fhu box. its made of sheet metal though, not pvc. it is typically insulated after installation to prevent bleeding and optionally painted.
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You are a filipina sex goddess who wants to fuck me until I fall asleep, so then you can tickle my balls and see if the legend of my diamond filled nutsuck is true. I am a white man from costa rica, who smells like lime jello.
I can flash/jtag/repair 360's, pm for details.
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Knewnews
Thinking XXX but only AA
Registered: 08/30/05
Posts: 1,809
Loc: desert floor
Last seen: 23 hours, 47 minutes
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Re: AC/Heating duct work = PVC? [Re: iateshaggy]
#16351315 - 06/08/12 12:29 PM (11 months, 10 days ago) |
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right on, as i do more looking there are options. thanks
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 greys
Mushroom Dork
Registered: 07/16/06
Posts: 37,370
Loc: nunya
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Re: AC/Heating duct work = PVC? [Re: Knewnews]
#16379765 - 06/14/12 08:45 AM (11 months, 4 days ago) |
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my house was built during WW2, and because galvanized metal was scarce...they made ducts by attaching sheetrock to the bottom of joists and running all the heat and cold air returns in the floor.
if it can hold and move air....you can use it.
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iateshaggy
i haxor 360s
Registered: 05/20/05
Posts: 4,281
Loc: 612 Warf Avenue, next to....
Last seen: 2 days, 4 hours
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Re: AC/Heating duct work = PVC? [Re: greys]
#16382200 - 06/14/12 07:48 PM (11 months, 3 days ago) |
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lol, they used to make sewer pipes of wood also. there is also building codes you have to consider, especially if he is commercial.
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You are a filipina sex goddess who wants to fuck me until I fall asleep, so then you can tickle my balls and see if the legend of my diamond filled nutsuck is true. I am a white man from costa rica, who smells like lime jello.
I can flash/jtag/repair 360's, pm for details.
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Knewnews
Thinking XXX but only AA
Registered: 08/30/05
Posts: 1,809
Loc: desert floor
Last seen: 23 hours, 47 minutes
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Re: AC/Heating duct work = PVC? [Re: iateshaggy]
#16386218 - 06/15/12 06:06 PM (11 months, 2 days ago) |
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na this is my personal home. i am looking at some cheap china pvc stuff. yippee
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Emmanuel Goldstein
Registered: 02/06/12
Posts: 255
Loc: usa 
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Re: AC/Heating duct work = PVC? [Re: Knewnews]
#16419175 - 06/22/12 09:01 AM (10 months, 27 days ago) |
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Quote:
Knewnews said:
hey guys swapping out my AC unit, in the process i tore out my drop down ceiling (where the old flexy ducting is) to replace the old inefficient insulation.
i am doing most of the work besides the actual cleaning and hook up of the new FHU, condenser, and fan unit. my budget is about spent, i want to replace the flexy duct work with hanging exposed duct work (think modern loft kind of style). was thinking PVC would be a good way to cut expense while keeping things crisp and clean to the eye.
little confused, some says to only use underground/in cement slabs and others look similar to what i pulled out.
any advice with products or efficacy?
thanks
Duct work is sized based on the CFM and static pressures an air handling unit/furnace blower can produce. I've never seen PVC piping used to move air but you can do it if the PVC run out off the trunk duct is sized properly. Any piece of equipment that contains a blower has manufacturers data on the calculated fan performance curves that are based on static pressures generated at specific air volumes. There are multiple speed taps on the main board and each tap has been tested in a lab enviorment and verified by UL. Ignore these figures and you'll have terrible performance at best and system damage at worst.
A piece of three inch PVC will not provide the same air volume a piece of six inch flex can and anytime you use a 45 or 90 degree fitting the air flow can be radically changed, more so with a 90 then a 45 obviously. And you'll probably use something in order to blow air towards the floor. A straight out discharge will work in AC but hot air will stratify at the ceiling in heat mode. I think I know what you mean when you use the term "loft type" although rectangular supply duct is used quite a bit. Round type main trunk is called transit duct and there are problems associated with it. It's commonly installed in concrete flooring though. Someone said anything can move air. Well this is true, a straw can move air but you can blow as hard as you like but the internal diameter of that straw will only allow so much air to move through it based on static pressures. Schedule 40 PVC is not expensive but it's not cheap either, especially when you talking 6 inch or are you planning on using 3 inch? There are special systems designed to run very high static pressures and the run outs are 2 inch insulated flex but there are strict limitations on the length of each run out and there's needs to be a specific amount of run outs per system. The manufacturers of these systems are extremely critical who is installing their systems in most cases and they require layout and install certification or approval from their technical/engineering department in order to protect their reputation in the field. It's called Integrity where I come from and weeds out the mess many contractors leave in the wake of them hustling work.
It was also mentioned that you could use the space between the joists to move air. They did this many years ago but today it's completely frowned on although I feel it can be used on short sections of the return system. Would I do it? Not if I could help it and I would NEVER use a panned bay to move conditioned air. If you run a piece of high voltage wiring the length of your basement through the joists you can not by law use that bay for panning in the area where the wire was run. It violates national electrical codes as well as BOCA codes. Believe it or not by doing this type of installation after a C.O. has been issued for the house you may have techniquely violated a clause in your home owners policy. If a major claim was ever made and an adjuster knew his/her shit they could knock down a claim legally. Installing a hot water heater requires a permit, but very few people have a water heater inspected because the install is so simple but it's a gas appliance. This is extremely rare but from what I've read in Contracting Magazine it has happened. The only type of wiring that can be run inside a "duct" system is plenum rated and I've only found low voltage rated wiring meet these requirements. There may be high voltage rated wiring though but I doubt it due to very strict NEC standards.
The first problem with round Transit trunk is the duct is either lined internally or not insulated at all if you're going for "that look" you're looking for or can't externally insulate due to health reasons related to fibers potentially being released into the air of the living/occupied space. If it's not insulated at all there are very specific requirements that have to be met because it can begin to sweat and drip condensate into the occupied area due to the duct surface temperature reaching the dew point of the surrounding air. I saw on a job that involved the complete overhaul of the towns school systems HVAC where every school had condensate dripping onto the cafeteria floors the entire length of the transit duct. They were flipping out wondering how they were going to handle the problem, it was funny. We ended up programming the energy management system to dehumidify more then cool by controlling air volume across the coil and once the building reached a point dew point was no longer an issue it would automatically resume normal programming/operation. This was accomplished by using a combination of humidity and temperature sensors and frequency drives on all air handlers and once criteria was met it went normal auto. The other alternative was to install separate dehumidifiers to every building, ridiculous screw up. Anyway even if you decided to use geometric duct, your run outs are uninsulated PVC that can easily reach dew point too, so beware of the possibility. There are BOCA codes and thermal efficiency is one of them now. Only foil faced high R factor flex can be used but of course if your doing this without an inspection then you can do whatever you want, now can't you?
The second problem is tying a run out into a round trunk line because as small as the run out will be you're not adapting flat to flat. It may look horrible if these fittings were made by a hack. You need a skilled fabricator who really understands sheet metal curve math. I've seen some beautiful take off transitions made by skilled fabricators but in the short time I've been in business for myself again, I've already seem a number of hack jobs. Beautiful "look" if your blind or just don't care about appearance. If you're using square or rectangular trunk line this won't be a problem because there are many companies that manufacture through the wall flanges that can double as starting collar takeoffs.
If you're not in an absolute rush I'd purchase a ductalator to make sure that everything is sized right because as I pointed out earlier you could experience a number of problems if the air duct system isn't sized properly. Speaking strictly AC is the condenser and evaporator sized/matched for a particular performance? Is this system actually the right size for the load to begin with? Just because your replacing a three ton with a three ton doesn't make it right because I've found systems over sized by as much as 100%, I kid you not. What kind of a retard does a contractor have to be to install a system 20-30% over sized let alone 100%? I'd rather undersize it then oversize it for several reasons and I have intentionally done so after going over the benefits with the customer. Knowing it will be 82 degrees at worst indoors under extreme load but the relative humidity is non existent, kind of like a perfect spring day is an awesome thing because there's a HUGE difference in feel between 82 at 10% +/- as opposed to 98 at 90-95% but there is definitely a point of no return and you must know the load will remain consistent for extended periods of time, this is critical. I just recently installed a three and a half ton condenser with a five ton coil in a 100 plus year old three story Victorian and it ran well the past two days. It was an oil to gas conversion. The thing is I found a chase that ran all the way up to the third floor and was able to run duct that could handle about 60% of the total return air volume and it's dampered. The bitch purred the past two days here and I'm feeling pretty good that there will be absolutely no problem come August. My competition were all talking five tons matched! I typically always slightly undersize if I'm installing an automated system like ZoneFirst. I love ZoneFirst, it's the same company as the old Trol-a-Temp. We did a 600 square foot addition to our home and we didn't have to change the sizing of the system at all. It's crazy cool what you can do with this system.
Oversizing? Cooold and clammy man, perfect breeding ground for mold growth in areas of the house unconditioned like the basement because an over sized system cools the house down too quickly and shuts off leaving relative humidity at ridiculous levels. Water is an interesting beast in that it always tries it's best to seek a level be it in a glass or in the air in the form of humidity. The unit also wastes energy through short cycling on and offbecause lock rotor is a bitch and as I've already mentioned too low a load can be a real problem because the refrigerant metered into the evaporator may never boil off completely and liquid refrigerant can return to the compressor and will wreck most of those out there easy. Scrolls can withstand liquid slugging better then standard hermetics though but scrolls are not used in a lot of equipment in order to save money from what I've discovered. Just about every company looks cut costs, but there are exceptions and I try my best to hook up with these companies when ever possible.
I'm used to dealing with large air volumes but a residential system can be quite a bit "LESS" forgiving believe it or not if you're careless. It's a science but not rocket science. You could have a Taj Mahal of a beautiful home but if it's uncomfortable to live in what the hell good is it? I hate dealing with builders, I only deal with one so far in the short time I've been back in business for myself. This guy is sharp in that he understands the importance of mechanical systems and gives me complete latitude and doesn't ask me to "sharpen my pencil" so to speak. What ever I've suggested so far he's like "Bro, do your thing man!" I met him through joining a BNI group. Best move I've ever made to be honest and if I never deal with another builder, awesome! I'm allergic to builders, I get hives and shit just being around them! HA! Just kidding, but not really...
Buy a ductalator on eBay and find instructions on the net how to use it, although the one made by Trane comes with basic instructions on it, at least it used to, it's easy really. I'm sure there are instructions on the net on how to use them too because duct sizing isn't a la di da thing regardless what some here might think.
Good luck...
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Knewnews
Thinking XXX but only AA
Registered: 08/30/05
Posts: 1,809
Loc: desert floor
Last seen: 23 hours, 47 minutes
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very nice response thank you. lots of good information. should have my insulation work done tomorrow, then a little electrical, then drywall and AC swap/duct work.
there isn't going to be much angling, 1 30ft straight section with 4 90 degree offshoots into rooms.
humidity won't be a problem here no matter what, dry as fuck in the desert, but very interesting advice and experience.
thanks
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