Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit

Main Vent- Hoffman 45

Sorry for the giant pic.....I don't know how to shrink it.

This is the main vent of my system, might be untouched since the house was built. It is a Hoffman 45. I removed it and blew through it. It has a small orifice and doesn't allow much air through! I have a Big Mouth on order.

This vent seems to be way too restrictive for a main vent. Am I right?

Does the mounting look ok, or does it need to be reworked?


  • Jamie Hall
    Jamie Hall Member Posts: 17,084
    The mounting is OK. The Hoffman 45 was dandy when the heat was coal. Too small now!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Fred
    Fred Member Posts: 8,518
    You'll notice a big improvement with the Big Mouth!
    JUGHNE Member Posts: 8,949
    Personally, I like the giant pictures....wish they were all like this!
    Much faster to view and review.

    Yep, vent too small....big mouth will be a great change.
  • dlipter
    dlipter Member Posts: 59
    Interesting that 12 years ago when the boiler was installed, the installer (my oil delivery company) never bothered to look at this main vent, didn't install a low pressure gauge or vaporstat.
  • Steamhead
    Steamhead Member Posts: 14,840
    Doesn't surprise me. And, that Hoffman 45 is a convector vent, so it probably has even less throughput than the usual 4A.
    All Steamed Up, Inc.
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • dlipter
    dlipter Member Posts: 59
    How is a convector vent different from a steam main or radiator vent?
  • Fred
    Fred Member Posts: 8,518
    dlipter said:

    How is a convector vent different from a steam main or radiator vent?

    Much, much smaller venting capacity compared to a Main vent and it is a straight vent compared to angle vents used on radiators.