Problems with flex duct 

My dad and I discussed this many years ago. Not being HVAC techs we weren't sure. Thank you! And Happy Father's Day!

More videos like these good sir. Thank you

I’m a DIY type and I use hard duct with insulation wherever I can when retrofitting my 100 year old house. The only place I used flex duct was installing retrofit jump ducts from the upstairs bedrooms to the hallway. But I used a larger diameter than the supply ducting to compensate for the added friction.

Here in australia we used to have flex ducts with a semi rigid perforated aluminium core (like the dryer ducts you have in the states) They were insulated with fiberglass and a clear polyethylene sleeve. They had very low friction loss and never sagged. That style lasted from the eary 70s throug to the late 80s when interlock was introduced. That had a silverish tarpaulin type fabric core and a mechanically locked wire and plastic channel. They were very good. The semi rigid ones forced installers not to cut corners and make tight bends and squash them. Although I have seen them kind of crushed to fit but not as bad as modern flex. If you look up "flexmaster triple lock" thats pretty much how it was.

Great video GFM. We need more like it when you can.

Great video, GFM! In FL, I've seen the worst installations for Flex duct. I agree with that sheet metal elbow and then the flex connection to increase airflow. Im a longtime fan of your videos. Hope all is well. Take care!

Good info especially the stretching right out of the box

i noticed these little quirks of flex ducting recently when i reran my basement dryer line.. did it on the cheap cause its electric and its one of the newer driers with many temps and i never use more than med, the run is entirely plastic flex and it flows better than the old foil flex the previous owner had in there. and i suspeect its because its nearly a straight run with only one bend thats not tight at all. the previous one had a huge sag in it where im sure lint was building up and pulling it down further

Good to hear from ya GFM ... Nice little vid with good info ... Thx

those bad installed flex ducts, remind me of being a kid, where we smashed in a random 150K furnace into a tiny house(bad #1), then where the ducts didn't line up and had to clear main beam, four elbows in roughly 90 angles to go down around and back up... yeah, that's what happens when you have your son and his friend(me) install things at age 14..... 🤣 we actually repaired multiple 2 line deep well pumps (in well ejectors) back then also. but those were pretty easy, check depth to make sure footer valve wasn't in muck and repair the leaking poly pipes, pumps or various parts. those were easy at that age. man are still working to this day(30+ years ago now), some had issues, from brass corrosion (pinholes in ejector or footer valve).

Hello Grayfurnaceman! Long time I haven't heard of you.

Great video, thank you. I wish that I could find flex duct with a better insulation value than R8. I have flex duct in my attic, and there is significant unwanted heat transfer between the duct and the attic on the longer duct runs. I find it interesting that while the ceiling has R30 insulation (I believe), the duct work in the attic only has an R-value of R8. PdZ.

there's a problem with stretching the flex ducts on install, they shrink and break down with age, ripping apart at random places with normal airflow! that may very well have been the case in many cases. more or less, they need a flat trough or "bed" to lay upon, when only supported here and there or by wide strapping failure is inevitable. new ducts in my own home? 99.9% hard piped. sans insulated bathroom exhausts (minimal temperature fluctuations). not afraid to knock tin and did an "ten times" way over my head job, in an tight space commercial building attic, not only that, in below 10F weather, effectively removing the only heat for the large building full of glass front coolers. sweating bullets and knocking tin like mad, re-using existing ducting to re-make transitions for new gas duct heater. sweating bullets x900. got it done after way too many hours. their other options were remove roof or remove ceiling and all multi rows of wine shelves and other products below for a big lift to fit and remove old unit. I had to bang apart 36" square duct and two 16 x 32" to move it away and built an rack/storage sled to hold the old giant unit heater. I should have never taken on the job, but I did and got it done in about 12 hours straight.

I haven't worked for any company that would let me take the time or extra money to use elbows like that.

How do you deal with ducts sweating when you lay them on a plywood runner?

good old ribbed noodle ducts, restriction 1 of 1

The duct work in my house is awful. The unit is lower and all the flex come out and go higher and bends all over the place. Should install elbows to help it circulate better?

The real question is what is the static pressure of a crushed flexible duct ….. Answer: it depends how crushed it is … I do know however , that adding an adjustable 90 is equivalent to five additional linear feet …thus increasing the load on the blower potentially …. So adding a 90 could be worse in some instances….although it will prevent crushing

👍 It's a shame that you have to do a video about fixing installers' work. They should know better.

ducts don't belong in hot/cold attics anyway - there's always a way to avoid but builders are cheap!

great examples of hard pipe elbows and straight flex pipe on "flat surfaces". being cheap and fast is what made them "great". just like everything else cheap and fast, the failure rate is giant right from the start. also rodents cannot chew through, nor enter proper hard ducts 🥸