I need to replace the vent pipes for my hot water heater and furnace- they're 3", 4" and 6"diameter and made of sheet metal. The duct assembly is held together with short sheet metal screws-- and I'm not sure how to start the screws in the new vent system.
I always thought sheet metal screws were self-tapping but doesn't seem like you could push very hard to self-tap without bending or crushing the pipe- especially the large diameter ones. Do I need to drill a pilot hole or what?
Joe
You can drill a pilot hole, but if you get the hex-head screws that have a very sharp point, you can drive them using a cordless drill (or corded, it's just that most people seem to use the battery stuff these days). They will spin against the metal for a short time and then bite in. That is in fact what most people do. If you want to use screws with a phillips head, you will have to drill a pilot hole.
Actually both the drill and the "zip" screws bend the pipe somewhat, but it springs back.
Sheet metal screws are self tapping, in a sense, but most of them are not really self-drilling. These special sharp screws work ok with fairly light material like ductwork.
You need a pilot hole. Pop rivets work well too.
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