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Info on conversion of steam to hot water of a two pipe steam system

Kmac Member Posts: 5
Anyone have a good reference for a project such as this.

I've been working in a residential single family that's been slowly remodeled over the years. It's got a huge steam boiler supplying steam to three floors of radiators. The first floor has a combination of radiant, steam, and hydro air. Yes all three. Radiant run off a water heater, hydro off a zone off steam boiler. The third floor has a/c and they want to add a coil for heat and do away with some of the radiators.

In my opinion it's time to convert the whole system to hot water, but I've never done it. It's a two pipe steam system, I'm sure someone out there knows what to do. I could use some guidance



  • Steamhead
    Steamhead Member Posts: 16,726
    Do you like living dangerously?

    First, the steam system runs (or should run) at less than a pound (this sounds like a Vapor system). In a three-story house, a hot-water system will need 18 pounds to get the water to the top floor. This is eighteen times the pressure of the existing system, and if there are any weak spots in the piping or radiators, they WILL leak. I've seen a few of these and won't touch them- too much liability.

    Second, the radiators may not be big enough to heat the rooms with hot-water. A steam or Vapor radiator gives off 240 BTU per square foot EDR, a hot-water system only 150. And if you try to run a condensing boiler on this type of conversion, it won't condense much since you'll have to maintain higher water temps. This takes it out of its high-efficiency range.

    Third, the return piping is probably too small to carry the water needed to heat the radiators properly. Have you figured in the cost of replacing all this piping?

    If you "must" put a hot-water coil up there, run it as a hot-water loop off the steam boiler. And if you do, be prepared to deal with complaints that the coil setup does not provide the comfort that the radiators did.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • Jamie Hall
    Jamie Hall Member Posts: 22,918
    Got to admit...

    If I were faced with something like this... I'd be very inclined to recommend to the client that the only really sound way to do it would be to take the existing mechanicals -- the whole lot -- out.  Might keep the radiant floor piping, but certainly not the water heater...  And start all over again either with high-efficiency hydronic (including new radiation) or perhaps with some sort of heat pump system...  I wouldn't try to use any of the existing radiation or piping, although you might get lucky and at least not have too many leaks.  But it would still be a camel.  Much easier to do it right from scratch.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
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