Rigid Metal vs Flex for HVAC Ducting
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- Опубликовано: 21 фев 2012
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For more information see my blog at www.risinger.blogspot.com Flex duct is super common in residential construction but it's not the best way to move air. See how my crew uses a mixture of both for the best duct install for the money. -Matt Risinger , Risinger Homes in Austin, TX
Seach plan contains all the components of the perfect shed plan ruclips.net/user/postUgkxB7IXYxLzb_Ichhe45zM3Im5xfEiSp9vB that i showed you above. This includes cutting lists & tools, with clear labels showing what each item is used for. (so you can buy just what you need, budget better and multiply your floor space). So the shed ends up just clicking together at the end. Every part will fit perfectly. You see from all angles, what each part is supposed to look like before you start building.
I really appreciate your strong voice for quality.
Matt, I did this in a 3rd floor apartment for my parents - rigid insulated trunk & plenum with insulated flex to the ceiling registers. The air blew strong and silently. You're right on the money!
We have been considering metal as my son does commercial AC management. The short, direct video sold us! Great quality and concise video!
Thanks for watching, it takes a special person to be geeking out on ducting options! Glad to have others like myself out there. Funny how I tend to attract clients who are engineers. Best, Matt
Thanks for the comments Paul & Phil. Yes lets get the word out to our builder friends! Best, Matt
Thanks Matt. It helped me address some of my hvac issues in my 42 year old house.
Planning to build my first house and I find myself watching your videos often. Thanks!
Excellent show, and when I want to know how to do something right, I turn to your advise. Thank you. Keep up the great work.
Man I’m actually in HVAC school as I speak this is really helpful
Great video. You clarified the duct work questions i had in my head
We just did a house fully with mini split systems. We used the Mitsubishi Multi City system and we used their conventional air handler so we had the best of both worlds. The really nice thing about this job was that we were able to link it to the web and the homeowner controls it from his iPhone app. I really like you 10' max on flex runs. Great job on the video. Good luck with your future endeavors.
As a rule of thumb, I install no more than 5 feet of flex at the end of runs, and absolutely no flex if I can get away with it. Great video and solid advice.
Very timely advice. Just found out to today that my flex duct was trashed by pests and are wide open in spots. Trouble is they are located in a low crawl space. All work must be done either flat on your back or on your stomach.
Great video as always Matt.
The more we educate on this topic, the more other people will care too! The general public has no opinion because they don't know any better.
Thanks for commenting. Best, Matt
I really like the ductless mini-split systems. I've not installed any LG units, but I've put in quite a few Mitsubishi mini-splits and low static pressure forced air units. They are amazingly efficient systems and have a TON of benefits over a standard forced air system. I visited Japan a few years ago and every house I visited was heated and cooled with Ductless systems. They do cost a bit more, but the savings and control I feel are worth it. The down side is the aesthetics. Best, Matt
They now have cassette style venting so the unit you used to see mounted on the wall is now recessed in the ceailing/attic, and the aesthetics are no more a issue. Also, they are actually MUCH cheaper, BUT the industry regulators have forced the price up. They are less than half the price. The install is more, but the units made in Japan for the S American market is excellent as all of SA uses them as well as Asian countries, and they are about $600-900 per 18K btu cool and heat units running 23+ SAR
Matt very well done on your video.I have been in the HVAC industry for over 30 years and you are right on track!Rigid duct is by far the best way to get every dollar out of your HVAC system.Minimizing the flex length,I usually stay around 6 to 8 feet in length,should be a standard practice.Unfortunately flex is quick to install and unfortunately to many contractors are in a hurry and want to get the job done and move on to the next paying customer.Homeowners do your research and demand rigid.
Excellent Comments Paul. I don't typically do filter grills for aesthetic reasons, but your comment makes sense. I'm using metal duct in the return and avoiding duct board at all costs. I really like the April Aire Media air cleaners, check out my other video on those. -Matt Risinger
I actually seen a return air plenum made of metal wrapped w/ duct board tapped w/2 16"round connections first for everything I guess.
Thanks for the video! It helped me in my project.
A lot of people overlook the diffuser.
The celing defuser is rated at 50cfm for 12"x12" regester.
Usually 1 regester in every room won't flow enough cfm of conditioned air and will cause the ductwork to spring leaks.
Great video !! Thank you for the information and explanation..‼️
great video, very informative. Keep them coming.
Got it! Thanks for the advice, Matt!
Sorry to hear that. I would suggest you first get a Duct Blast test performed by a BPI Certified energy rater to find out just how leaky your duct work really is. They can likely suggest a good contractor who can do some air sealing work for you. A new home should test down to under 10% duct leakage, a well built system like I install is under 5% leakage. You'll never get to 0%, but if your house is older (10+yrs) a good goal would be taking your leakage to 12% or less. Best, Matt
Thanks Matt for the great content.
Very cool! I've got several Mitsubishi systems coming up and I plan to do some videos on these installs. Your system sounds fantastic! What part of the US was that system you installed? Best, Matt
Great Video Matt.
Nice to see someone with standards these days! We're replacing our new home flex with rigid pipes for better flow and less dust! Can't wait!
awsome , wow great man, now I have to find somebody that will do that, wish you can do it for my house,
Great looking work!
This guy is spot on. Flex duct is used because it's: 1. Cheap. 2. Very fast install. 3. Allows for inappropriate installs for speed (i.e. weird bends, etc. to make install easier for the installer, yet the homeowner pays for it for decades for friction created and loss of energy). Very good video.
gone-shootin' not to mention the plastic becomes brittle and falls apart. in 8 years time.
Excellent Video!!! Great Information!!
you're gonna get a great install
love your videos... and watched lots of them. i built a camp 4 years ago, and did not do an erv install at the time. its one level, slab on grade... can i run insulated flex over top my attic insulation to supply bedrooms and exhaust bathroom/kitchen? i'm getting a lot of condensation on my marvin integrity wood windows, and thats not a good recipe at all. no problem when camps sitting on 12deg c when not in use, but as soon as getting there and bringing heat up to 23 with wood or elec obviously on cold days im getting some real problems.
"Metal trunk lines and plenums and limit flex duct to 10' or less at the end of the run" That's very good advice. I wish the HVAC contractor who replaced my system several years ago had that same commitment to quality - and I used a well known "reputable" contractor. {{{sigh}}}
I've seen old comm. lines pulled w/out regards to insulation being compromised and flex lines choked off installation of both can be goofed up much less design and size issues of course.
So great to see the same quality content even 11 years ago, so cool to see how you’ve developed as a presenter. Bravo.
Hey, what is the rule of thumb when selecting the right dimensions of the floor register i.e I'm using 7 inch rounded metal duct. Thank you!
Good Video! I personally only use flex on very short runs and to insulate round ridged ducts.
Hey Paul, I got out of designing all flex (or, Owl Flex) duct systems years ago mainly because of airflow issues. Not only because of the material itself, but because of the way it was being installed in the field. The field workers were getting carried away and not installing the flex per the standard of care. So now I use metal insulated main supply trunk lines with flex branches and flex main returns (in attics mostly, bsmt's are all metal). More builders should see this video. Phil
philmiller99 rats chew right through this crap.
They used to make a flex duct called JPL. It had a scrim cloth interior that was not air tight. If you got a tear in the vapor barrier, it became an air leak. This crap fell apart inside due to airflow erosion. We had a whole commercial building installed with it, and it all had to be replaced within the first five years.
Very timely video... we are getting a system installed SOON and they're pushing duct board main trunks. Do you know of any known air quality issues with that stuff? My Dad is on oxygen as it is and certainly do not want to cause him more problems.. Thank you
Hi Matt, I saw a few 90 degree turns at the end there, I'm just wondering what the code was in your area for that? Is it more lenient than dryer venting and do you try to us as much 40's as possible? Thanks.
the only real benefit on flex is it's easier to install if someone doesn't know how to join and hang metal runs. we just did a house on Tuesday that had 100% flex in the crawl space. had it all torn out and half the house ran with rigid by the end of the day, finished the metal runs and mastic on Wednesday. it cost the client a little extra but it's well worth it.
I know this is an old video, so I can only hope to get a response. I have a house that was built in the 20s. My ducting is made of metal and rectangular box shaped. Wrapped in asbestos to top it off, although most has been properly removed. I would like to replace all of the ducting but am not exactly sure what to do because I am limited to the same shape that I already have since it has to fit between the Joyce's. Should I just replace it exactly as is, or is there a better option? I would greatly appreciate some feedback on this.
Great Vid. Can you recommend anyone in the Houston area to replace existing flex with rigid? I've had my ducts cleaned over the years and now it appears they are starting to fall apart.
Don't assume that you'll get rigid metal trunk lines, very few HVAC contractors do that. Tell him you want flex drops of less than 10' in length with all else being rigid metal. Best, Matt
Why 10 feet? As a PE we would not accept anything more that 3 feet, but only when you want to relocate a diffuser say in a ACT ceiling
Thanks for the video Matt. I'm in the process of remodeling my home which was built in the 40s as well. I have taken things down to the studs and am currently debating how to run the new HVAC system. I plan on completely starting from scratch as the old system was added to and patched together over the years. It's extremely ineffective. I have just came across the new LG ductless system, have you heard anything about that?
Hello Matt,
So good to find you! I bought a 1904 home in the low country of South Carolina. I have 2,000 sq. ft. of crawl space with very old metal ductwork and shredded insulation thats wetttt. I have had 3 different contractors look at it. 2 want to replace with flex stuff and 1 wants to use metal with 3" insulation. I want to use metal man (gut feeling) and then you really convinced me. Well, metal man (40 yrs. in heat & air) said he was afraid when replacing all ductwork, they have to move the 3 units for connecting and the old units might not work afterwards? What what what am i suppose to do under those circumstances?
I hear a Carolina Wren! Lucky homeowner!!!
Metal duct work was installed in most homes in Texas until mid 80's then atco vinyl spiral flex was introduced, which after 6+ years would split open in heat. Foil back spiral flex then came into installations, and duct/board. Sound will resonate through metal so it is good to tip duct at the ends with flex. Take from Ole Timer 1970's hvac man. Metal is better static flow and out last flex.
I was just checking my flex ducting and I can feel a little bit of cool air coming out of all the connecting locations. Is that normal to feel a little bit of cool air come out like that?
Great info
Hi,
Thank you so much
Matt, hopefully you can show us some tips for upgrading old balloon frames.
Normal, yes. Correct, No. That's duct leakage and you want to seal those leaks up. Air that's leaking out isn't going where it's intended. Best, Matt
Hi Matt, thanks for this video.
I have drawn up a concept for a Local Exhaust Ventilation system that I will install in a nail salon. However, I do not know how to select the proper duct sizes, as I do not know how to perform the fluid dynamic calculations (calculating static load) of the network. The system is rather simple: think of an ant; At the head is a centrifugal exhaust motor mounted adjacent to a wall that it exhausts through to outdoors. And at each foot, I need to provide a minimum of 50 cfm volumetric air flow. I will have in-line dampers on each ankle, and a rheostat to control the motor for control. Any suggestions on how I should determine the duct sizes at each branch, (and ultimately select the correct fan capacity range)?
Thanks, James
I never saw flex until I moved to the south. Up north with basements we just run uninsulated rigid in the floor joists.
what type of ridge and eave vents are you going to instal in that place?
what refrigerant charging techniques do you guys use?
Matt? Can I get a good spray foam insulation job in my walls without completely taking down the walls? Does it work well to just take the walls apart from the outside say when residing the house?
What do you call the wall unit cage on the out side to protect the air conditioner or from thieves pushing in the air conditioner. Is it called a cage ?
what ducting systems do u use for sound proofing
Retrofitted a lot of older homes with existing pot soldered rigid ducts in them. 99% of the time I recommend keeping the rigid system and insulating to current State standards. Often they are (by current methods) undersized but found that sealing them is easily enough to surpass current min. requirements by 50%. Personally and in the field Blaster and hood testing flex duct FR is wholly understated, it's much higher than the marketing states.
Would love to see a video on how to insulate the rigid ductwork (I'll look around for one.). Had mine redone by a local AC contractor and it's sweating badly. Contract said 2" of wrap, probe showed anywhere from 1/2" to 3/4". I'm getting tired of re-doing sloppy work.
Yep which is why I'm learning to do my own work as much as possible
Hello there, don't mean to spam but I am. Have you done retrofits and how long on average before the customer sees the savings of the extra costs in the beginning?
I have used both as most of us here.....how do you do a proper duct cleaning when flex is installed?
I work with flex and we move it so it wont have restriction. We also put the mastic in the flex, attach it to the can, zip tie it tight, snip. Then bring the insulation over to mee the tie and tape it shut with flex duct tape. Then we insulate the remaining parts with brown insulation including the can if its showing silver thankyou. We have five stars on reviews on Google
How far away do you try to keep duct from drywall?
What is your opinion on using PVC for ducting that is only carrying cold air?
I agree. Metal plenums with short flex drops to knock down the noise. If it is all metal you hear noise from the metal expanding. Too much poorly installed flex duct out there.
Is it possible to do all rigid and no flex?
continued - He drew the trunk line (which I'm assuming will be made out of rigid duct) and the registers for supply and return, but he really didn't show whether they would use a combo of flex and rigid when branching out to the living, kitche bedrooms and bathrooms. Can I share that with you and perhaps you can suggest the best way to layout the combo flex and rigid. They did caveat that their methods were based on the manual d and manual J guidelines of the ACCA. Thx
Matt - I'm in the process of getting estimates for a new central Hvac for our L-shaped ranch home. No existing ductwork is in place so whoever is doing this will have a clean slate. I've sent the contractors a layout of the home and asked how they will be installing the ductwork.
You are correct sir,flex should be no more than 8' in length!!!
Mostly right, . And much better than most jobs.
We went all ridged duct.. mostly because we spray foamed the lines to make them air tight.. flex is so easy compared to ridged.. if you get a furnace guy to install “on the side” you can save a ton of $$$.
What do you think about P3 duct or phenol
Just had the AC company check my house out. I have a problem with one of the bedrooms not cooling. He said it was the box that distributes the air evenly in the attic and would have to be replaced. The quote was for 10,000 Dollars. Does that sound right?
@67tr876 Agreed.
I got a question. I've seen some people going with PVC duct work for their homes. It not only insulates better but there is less air loss throughout the system. So question how does one implement this system? I already don't have walls in my house since I'm renovating and I'm getting a new HVAC unit. I've heard you need a nonconductive adapter between the HAVC unit and the piping and proper ground for the tubing for static reasons.
Using metal clips to secure the PVC duct will help dissipate static electricity.
Also run copper wire through the inside of the PVC duct runs and ground the copper.
No sure about larger PVC duct systems, but a couple brands the specifically produce PCV ventilation duct are Fantech FlatPack ventilation duct and Verplas Flat Ventilation duct. Both use self seal connectors so they're relatively easy to install. There will be many other brands out there that specialize in this type of ducting.
That just sounds more expensive?
Hey Matt I’m having a contractor come by my house to give me a estimate on my HVAC system because the whole unit is shot it doesn’t work. We bought the house 2years ago but it was built in 1983 i want to educate myself more before they come . What advice do you have for me & i have duct my system is in the attic it’s a tight crawl space
@dogfan4lyfe Yes, they make a slow expansion "pourable" foam. You drill holes in your sheetrock and pour the foam into the cavity so it expands slowly to fill. Not many guys do this however so it may be hard to find a contractor who is experienced. Doing spray foam from the outside is also do-able when residing your house. Joe Lstiburek has done that before so you might look for some examples on the building science corporation website. Matt Risinger
Question, do you suggest having registers going out towards room or down from ceiling? Love these videos!
Hope got your answer depends though
Is it possible to clean 44 year old rigid ductwork?
Good job
I want to replace all the flex in the attic. Not even 10 ft flex runs. All will be sheet metal. How loud will the system be? I don’t like flex ducts at all
Thank you‼️
good to see that you're not going with low bid on your HVAC system for your homes but I would not use flex in a place where it's not accessible the Flex today is better quality than it was 40 years ago I have seen flex fall apart should just do it all in metal where you're going to be finished in enough not that much more anyway I've seen some really expensive homes in my 25 plus years in HVAC with flex. That's just been hacked in good to see that you're not going on the cheap
That is the correct application for flex duct. Use it for terminations only. You should mention, that flex duct that is used in attics and crawl space is very susceptible to rodent damage. They love to nest in the stuff. I would specify 6-7 feet max of flex duct and just at the terminations.
Metal will sweat in the green grass states unless the installation is perfect...it will also sweat anywhere the insulation is compressed (resting on a 2x4). They make high quality duct board that has a smooth inner surface. I did my first house in metal, second one is all flex and ductboard.
Is that going to be a conditioned attic?
What about rusting from condensation?
You can also use aluminum flex in residential.
Glad I watched
ur not doing the 2 inch stuff?
The house is located in the Southeastern North Carolina, Wrightsville Beach to be specific.
The metal duct will reflex the temperature of the supplied airflow because of it being metal as so whether it is hot or cold air., whereas the flex duct will absorb the temperature of the supplied airflow and discharge a totally different temperature versus what's being supplied to it. One other thing is the flex duct does not have a smooth inter surface which will create air rolling effects that are the same as turbulence, which creates resistance to the supplied air. So discharge air at the register will be off if not calculated properly.
Have flex duct in my attic the heat is strong going into attic but as soon as it goes into flex duct it losses all pressure
Is the rigid completely mouseproof?
I WOULD TRUST THIS MAN WITH MY HOUSE.