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where to ask a tin knocker question , this is the question

it isn't actually for scorched air, but for a vent cap. i'm looking for a 4" vent cap that is oversize enough on the receiver to just slide in 4" duct without a crimp. then i don't to figure the length and precrimp or waste a crimp off my last length (until i can find an affordable pexto, but that's a whole nother question).

maybe somebody here has sussed this out or knows what wall the tin knockers hang out on.



  • AMservices
    AMservices Member Posts: 597
    What are you venting and unless you wanted to pay a fabrication shop to make a custom rain cap, you won't find what you are describing.
    It would be much cheaper buying a hand crimping tool
    HVACNUT Member Posts: 4,194
    The termination end piece should be crimped, not the cap or hood. A crimped end should follow the direction of air flow.
  • archibald tuttle
    archibald tuttle Member Posts: 819
    i get that. what i'm looking for is a termination that would have a diameter big enough to accept the 4" duct without a crimp. so the relationship of the pipe and the cap is the same. the cap goes over the pipe. it just means i can leave a pipe end coming up to or almost to the sheathing with a quarter inch center hole punched through, allowing me to holesaw later from the outside and fit a cap on without knowing precisely how long the cap boot will be because they interleave. see, e.g. the two pieces of a wall thimble that slide in and out of each other with no crimp to allow for different wall thicknesses. to me this works kind of like an extended toilet flange so you don't have to perfectly settle the thickness of your floor finish when you rough in the pipe. then a little silicone on the inside of the oversize duct on the cap , slide 'em together done with no measuring or cutting and I save a crimp.

    and AM, i do have a set of hand crimpers. maybe there are better ones, but don't like the crimps you get with those. i prefer a pexto but haven't trolled ebay enough to get one for a decent price so i use the one at my local tin outfit.

    I didn't have time to pursue further so i just left a crimped end about an inch from the sheathing so i'll have to cut back the duct on the cap to allow for 1 to 1 and 1/4 overlap before i put them together. Not the end of the world or anything, but i have never liked terminating that way - inter alia because most caps are so cheap that if you push hard onto a crimp as they reach the least tapered end of the crimp they can fail, i.e. open at the seam and or the attachment of the cap to duct fails.

    I just think this would work better with an easier fit and silicone.
  • archibald tuttle
    archibald tuttle Member Posts: 819
    actually, now that i've spoken to all the plumbing pyschologlists here at the couch . . . eer the wall, it occurs to me that probably the smart thing for bathroom vents would be just to work out the standard for using light PVC and then get molded, one piece cap that glues over the pipe and has deep insert like an extended toilet flange so it covers a wide range of distance of pipe end from sheathing.
    HVACNUT Member Posts: 4,194
    > @archibald tuttle said:
    > actually, now that i've spoken to all the plumbing pyschologlists here at the couch . . . eer the wall...
    >> From my couch, it occurs to me, you could design a roof cap to your specs. with an extended 4" pipe, submit it to your local sheet metal shop, (a good shop can make almost anything) and have them fabricate them for you. Then you can cut it to the desired length at the job site.

    Or, you can just use a ruler. It pretty easy once you get the hang of it.

    Now where's that remote?