Fabing a supply plenum/return plenum and filter box

I can't tell you how to properly size the ductwork but surely there are places on the web with that info. But when it comes to galvanized sheet or painted sheet I would go with galvanized. I wouldn't weld anything. If you need to make custom duct I would suggest soldering. I did this in my house when I had to modify the installed ducting. I just plain couldn't find any stock ducting for a couple places. So I bought ducting that was as close as possible to the desired sizes and shapes, some flat sheets of galvanized steel, and a roll of the same stuff. I bent the pieces to size and I was going to use screws to hold it all together and that aluminum tape to seal the seams. The stock ducting was made so that the seams were sealed by crimping and I couldn't do that. And even though that aluminum tape is made for this type of work, and seems to stick forever (unlike DUCT tape) I decided to try soldering. The ductwork was amazingly easy to solder. So I soldered my custom pieces and only used the aluminum tape to seal the seam where my custom work met the original work. Eric

How did you solder it and with what? Does soldering not remove the galvanized coating?

Use a tinners iron - I have an electric one - the original "tinner's iron" was heated with a blowtorch. Flux the galvanized and solder it together - the zinc stays on the steel.

DON"T try soldering it with a torch. You WILL burn off the zinc, and it will rust bedause you will overheat the joint.

I soldered mine with a torch and didn't burn off the zinc. I used regular lead fee plumbing solder and paste flux. The solder melts at a much lower than it takes to burn off the zinc. You need to keep the flame moving. If you let it dwell it can then heat up a spot enough to damage the zinc. There are available (at least there used to be) soldering tips for a propane torch that fit over the torch head and use a screw to hold them in place. One of these would work very well for soldering galvanized sheet. Eric

I assume a propane torch?

A soldering tip for a propane torch sounds like a great invention. I have never heard of one.

I think I still have mine, which I bought 40 years ago. But I find my

An online search yielded zero results. Am I understanding it correctly, a tip that attached to a propane torch and the torch heats the tip and the tip is what you solder with?

I would love to have a hi watt electric one but they are rather expensive to buy for just one project....

Yes. The tip is ahead of the flame, and there are ports for the flames to come out of the sides of the tip, behind the copper part.

I found it very awkward to handle and use, but it would do the job in a pinch -- if it didn't catch something on fire.

Mine is at least 60 years old. It was used for soldering copper standing-seam roofs. I've used it for sheet-metal work and it's great to have that much heat. The tip must weight over a pound.

I also had four furnace-heated soldering coppers, which I gave to a collector some years ago. Those were great if you had a small foundry or furnace to heat them, but heating them with a plumber's torch was a pain in the rear.

I'm surprised , they've been around for a long long time . I've had them in torch kits I've bought , and Dad had at least one when I was growing up (and I ain't young) . I know this because he used it to solder radiators . He was a DIY guy , I learned from him ... I'm a DIY guy too .

I couldn't believe you couldn't find it, but I couldn't either. Here is what they look like:

I've had one forever, but never use it. Maybe nobody does & that's why they don't make them anymore.

Bob

I've seen HVAC sheet-metal shops bend up these things. Measure carefully, and get them to do the work: they're fast, efficient, and already know how. Check some local stores, see which filter sizes are well-stocked, and use one of those sizes, but you probably already knew that.

Soldering duckwork seems pointless unless you just like soldering for the hell of it. You can buy duct in L shaped sections that are pre-crimped and form nice rectangle or square sections. Screw them together and cover in the aluminum tape. They also make some sort of putty-like stuff for sealing ducts that comes in tubs, like drywall joint compound.

I have also had one "forever" and haven't used it in at least 35 years. But, if you want a really kick-ass soldering copper, take a look at