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Converting for Steam to Hot water

Sifin Member Posts: 1
Does anyone know if you could use a steam motorized zone valve in place of a hot water zone valve? I'm quoting a job that has two boilers one hot water the other steam, and a air handler that has a steam coil also. The steam system is a Hoffman type with steam traps. Feed and return lines. The steam boiler has a condensate tank for make up. I would like to install another hot water boiler and convert the steam system to HW. Also replace the current air handler to a more modern type Hydro air multi position unit.


  • Steamhead
    Steamhead Member Posts: 16,710
    Don't convert it

    unless you like living dangerously.

    The current Hoffman Vapor system was designed to run on half a pound of steam pressure. If it's currently running higher than that, it's too high.

    Hot-water needs at least 12 pounds, more if the building is higher than 2 stories. This much-higher pressure will find every weak point in the piping and radiators and leak all over the place. This tends to attract rabid lawyers.

    Even if it doesn't leak, the radiators may be too small to heat the building on hot-water. And, the return lines are probably too small to handle the flow needed for hot-water... etc. etc. etc.... My company does not recommend or perform this type of conversion

    If there's no danger of freezing and the AHU coil is big enough, it may be best to run the coil on HW and eliminate the steam zone valve.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • Jamie Hall
    Jamie Hall Member Posts: 22,877
    Why on earth

    replace a Hoffman system with hot water?  It would be like trading a Rolls-Royce in for a Yugo.  Just maintain the Hoffman right.  Save money and sleep better.

    On the zone valve, though.  If you have to have a motorized zone valve, or any zone valve, on steam, make sure that it's a full port type, either gate or plug.  Reduced port types, which work OK for water, may give some very hard to troubleshoot problems on saturated steam (which is what we're talking here) -- and globe valves are a definite no-no.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
This discussion has been closed.