Metal ducts seem cheaper than pvc. Am I missing something?

[Eric D Matson]

I called a local wholesale sheet metal hvac fabricator and told them what I wanted as far a wyes and reducers and what not. If I remember correctly, they charged me $6 for a wye. My fittings were all in the 5-7" range 24 gauge. I was more than happy. I sent them pics from Oneida's website and thats what they made me. It may be worth considering if you have a local supply house.

[Rick Pinzon]

Rick, I did do the "reversing" thing once and while it was doable, the result wasn't quite as good as a purpose built DC wye, although it was certainly a lot less expensive. There are a number of online sources for the DC wyes, so it's worth investigating who has better prices in the moment sometimes. The DC wyes also tend to be "gentler" sometimes and offer more combinations for flexibility. I've also found that the HVAC stuff requires a lot more work to seal...it seems they just slap the things together and don't worry about leakage...which makes sense for a positive pressure situation since any heated or cooled are that leaks still benefits the structure. DC purpose is less tolerant of that kind of thing.

what do you mean about gentler and combinations?

[Mark Bolton]

Do yourself a favor and avoid the home centers. Go with metal and find yourself a local plumbing or HVAC supplier that will sell to to you fairly for cash. You can buy 26 gauge round sheet metal duct up to 8" way cheaper than any PVC out there and unless you have a 20HP DC your never going to even remotely compromise 8" round even in 30 gauge. There is no way a reasonably sized DC is going to ever flatten 8" round sheetmetal even though you will hear warnings from the people who have bought home center aluminum foil duct work.

If you get away from the home centers you will immediately be dealing with heavier gauge material and have access to much more in the way of fittings and reducers.

We have an 8" main, that reduces to 7", then to six and four over about 80 or 90 feet. We too were wanting to have all spiral fabricated ductwork but seeing a quote for about 10X or more we went with our local suppliers. We were lucky to have accounts with them from the General Contracting world but most any of them will be fair with anyone. The only PVC we have in our system is in a trough formed into the concrete floor and we ran 6" sch. 35 PVC through the trough due to the damp/moisture issues in the trough.

[Mark Bolton]

what do you mean about gentler and combinations?

If you look at purpose built HVAC and DC fittings they will have very smooth transitions in directional and size changes. The aim is to keep the flow smooth and eliminate all the turbulence you can that robs your system of efficiency. You can come very close with off the shelf stuff but not perfect.

[Rick Pinzon]

I called a local wholesale sheet metal hvac fabricator and told them what I wanted as far a wyes and reducers and what not. If I remember correctly, they charged me $6 for a wye. My fittings were all in the 5-7" range 24 gauge. I was more than happy. I sent them pics from Oneida's website and thats what they made me. It may be worth considering if you have a local supply house.

I cant find anyone locally that makes them, best I could find are distributors

[Peter Kelly]

If you look at purpose built HVAC and DC fittings they will have very smooth transitions in directional and size changes. The aim is to keep the flow smooth and eliminate all the turbulence you can that robs your system of efficiency. You can come very close with off the shelf stuff but not perfect.

Also minimizing any hard 90° turns by using 2 45° elbows or 90° ones that are smooth stamped or long sweep. Oneida, Blastgateco and Kencraft have these. https://www.kencraftcompany.com/prod...-sweep-elbows/

Also want to spring for the better grade urethane hose as it generally has a smoother interior than the cheap PVC stuff.

[Jim Finn]

Thank you all for the feedback. I will update when I figure out what direction I will go. I definitely learned the there is a difference between hvac wyes and dust collector wyes. If I can successfully reverse the male and female ends by stretching and crimping would there be any other issues with using hvac wyes? $60-$70 per dust collection wye vs $15 hvac wyes adds up $

The way to reverse the crimp end of the HVAC fittings is to just crimp the large end and cut off the crimp on the small end.

[Jim Becker]

what do you mean about gentler and combinations?

The angle that the "drop side" comes off is gentler on some of the DC wyes I bought which makes for smoother air flow as that drop's air enters the main trunk. By combinations, I mean that you can do things like reduce and wye off simultaneously...and example, perhaps, would be something like a 6" to 5" and 3" for a table saw that has both a cabinet pickup and an overarm pickup. It's not a big deal but sometimes saves space for multiple transitions at the same point.

[John K Jordan]

Thank you all for the feedback. I will update when I figure out what direction I will go. I definitely learned the there is a difference between hvac wyes and dust collector wyes. If I can successfully reverse the male and female ends by stretching and crimping would there be any other issues with using hvac wyes? $60-$70 per dust collection wye vs $15 hvac wyes adds up $

I didn't study all the posts but in case this hasn't been mentioned: when designing your layout try not to have any vertical drops tie into a horizontal run on the underside of the horizontal duct. Dust and chips moving along the main duct can fall into the vertical drop and accumulate at the bottom. A friend of mine did that and when he opened the blast gate at the bottom of a vertical drop a pile of shavings fell out onto the floor. I ran my main ducts horizontally above the ceiling down the middle of the room and the wye at every branch came in from this side instead of the bottom so the branch duct ran horizontally for at least a short distance before dropping down. Works well.

Another thing that might have already been mentioned concerning losses due to inefficiencies and turbulence at fittings: a little extra power in the DC can overcome a lot of imperfections! I installed a 5hp ClearVue cyclone which was probably overkill for my shop. I had to make a number of compromises to shoehorn the installation into where I wanted it. It functions amazingly well! In fact, my furthest two runs to the lathe and bandsaw work so well that even when the 6" PVC main is split into several 4" ducts the bandsaw never has dust inside and I have to be careful to hold onto small turnings when parting off at the lathe or they are gone. In fact, when working at the lathe I sometimes crack open the blast gate at the bandsaw to reduce the deafening noise from the airflow at the lathe, with no detectable reduction in dust pickup. (I've devised a way to measure this.)

JKJ