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Replacing Main Vent

PinkTavo Member Posts: 64
edited January 2017 in Strictly Steam
OK...I have a Hoffman 4A right now. About 20 years old. Not sure that it is working well because my new radiator vents "hiss" too much, from what I understand. All radiators do heat very well. I was thinking of replacing this with a Big Mouth, but there may not be enough clearance, pipe to wall, to fit it in. I won't be able to just screw in the Big Mouth because the overall radius is much larger than the 4A. This is a small system. 210 Sq Ft of radiation. Would a new 4A work OK? I can't find its venting rate (CFM?). I posted last week, plan on adding a 2nd Main vent on the smaller branch this summer. Maybe two 4A's would work OK? Thanks for any help.


  • PinkTavo
    PinkTavo Member Posts: 64
    Here are a couple of photos showing the clearance.

  • KC_Jones
    KC_Jones Member Posts: 5,354
    edited January 2017
    The beauty of the big mouth is you don't doing the whole thing to install. The tailpiece installs with a 5/8" hex wrench and the the vent itself installs on that. No need to spin the whole thing so it could be a good fit for your application. As far as overkill on a small system maybe, but when you compare dollars to venting rate I don't think any other main vent can touch it.

    Edit: Height could be an issue, how much height do you have?
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
  • Fred
    Fred Member Posts: 8,540
    @PinkTavo , that Hoffman 4A vents at .26 CTM @ 3 ounces of pressure. That's less than a Hoffman radiator vent set at 4 or 5. No way enough for a main. Use the Barnes and Jones Bigmouth. As @KC_Jones said, you don't have to spin the whole body, just the tailpiece which is about the same diameter as a 3/4" union.
    If height is an issue (even though it looks like you have plenty height) use the Barnes and Jones Vari-Vent. It is shorter, probably about the same as that Hoffman, maybe a little shorter and about the same diameter and is about 10 times faster venting that the Hoffman 4A. The Bigmouth is about 14 Times faster.
  • PinkTavo
    PinkTavo Member Posts: 64
    edited January 2017
    OK. Thanks all! I am ordering a Big Mouth as soon as I get off this post. Height should be fine....I can always cut out some off the drywall. I did see a post about a tail-piece using an 5/8" hex, but didn't quite get how it worked. I get it now. Am going to use the suggestion of a 5/8" bolt head....instead of buying a hex for likely just one use.