1

I compared the black ducting for wood stoves with regular galvanized ducting and found that they are both 24 gauge and I noticed they are both steel since both tug magnets. There is quite a large price difference in addition to not as much stocked variety for the black pipe. The galvanized is ubiquitous with all sorts of adapters and sizes available.

Black pipe is available only in 6 and 8 inch diameters. I had an idea of spray painting the galvanized duct with high temperature resistant RustOleum. Would this work?

6

24-gauge is 24-gauge. However, the the silver type round pipe is coated with a rather inexpensive galvanizing coating. This coating is to inhibit rust. The galvanizing keeps oxygen and moisture away from the raw metal.These elements will discolor the metal, causing the metal to oxidize and rust, thus shortening the life of the metal. Now for the down side of you situation. When the galvanized coating gets too hot as in when used as a wood stove chimney vent the the galvanizing burns off and in the process produces a dangerous gas. If this gas is inhaled the result will be sickness and even death.
Sorry you are going to have to put up the money for the black stuff. Top coating this with paint no matter the quality is not enough to ensure protection against this off gassing.

  • I'm going to back up this answer, and stress again that this is not a wives tale about galv pipe. If this is going in a sealed space (like a home), DO NOT use galvanized pipe. I used galvanized for my wall tent stove, but plenty of air moves through those things. Once it burns off it's gone, but you don't want to risk this in your home. Also, galvanized surfaces need to be etched with something before they'll accept paint well. – slambeth Feb 8 '18 at 15:32
1

Yes, just remove all the zinc galvanizing using a well vented media blast cabinet. You'll need to do that anyway to get paint to stick.

Also check other vendors. Some people emotionally chain themselves to the local big-box store. They know this and stiff you on anything you're not likely to price check. I regularly catch them asking 3x what the thing costs at the electrical supply, case in point 120mm boxes or conduit barrel connectors. So try HVAC supply, stove supply if you have one, or your local lumberyard.

Also realize all magnetic steel is not the same alloy. Steel performance varies dramatically depending on the alloy. Some alloys are much harder to work, require hot vs cold rolling, or have expensive alloying metals. Naturally that is reflected in the price.

1

I say they are both poor choices . Look for 13 Cr stainless steel , it is magnetic ( what modern auto exhaust systems are made with ).Second choice is thicker carbon steel , galvanizing makes little difference . Because a wood stove can get very hot, I greatly doubt that any paint available to the consumer will help. Zinc melts about 700 F and then forms intermetallics with iron and stays on the pipe ( unless corrosion with water exposure removes it). Zinc starts to vaporize above 1600 F ( yellow hot - do not let your flue get this hot. ). Zinc vapor oxidizes immediately in air. Zinc oxide is generally no problem , wives tale aside. HOWEVER, fresh zinc oxide , less than an hour old , can cause zinc chills, = oxide shakes, = brass founders ague . Having had this myself , I can promise it clears up in about 48 hours. I should have said you want double wall flue pipe ; stainless or carbon steel.

0

You cannot use HVAC ducting for a wood fireplace or stove exhaust. The stove/fireplace exhaust parts are typically triple-wall and are totally different in terms of their construction and connection methods. HVAC ducting is simple single wall sheet metal with leaky joints that you cover with foil tape.

It's not an issue of galvanized vs painted.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.