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Steam boiler with baseboard & radiant floor.

Snowmelt Member Posts: 1,415
I may have a job where the existing steam boiler is supplying steam for the home, also domestic water, 2 zone baseboard and one zone radiant floor. The radiant isn’t hooked up but the baseboard is, I think when the customer redid the kitchen and family room they added the radiant floor. I noticed the 2nd zone of the baseboard does not get warm. I think it just has to be recipes in the basement with a separate return with a shut off and hose bid.

The question is when I put a new steam boiler, by the way going from oil to gas. Can I or should I use the add a loop which I did twice in the past but put a flat plate hex with a bronze B & G 100 pump on the side of the steam boiler and on the baseboard/ radiant floor side put a pump sized properly for the baseboard and radiant floor. Which look small.

If I add my rads and get a total of 75,000 btu of steam an about 8,000 for baseboard and both numbers are high. So I am not talking about a big boiler at all. Only one shower in house so there is no domestic water problem.

I don’t think they want a tank water heater either.
Give me some idea of what you would do.......


  • Jamie Hall
    Jamie Hall Member Posts: 23,289
    That 8,000 BTUh for the radiant is well within the pickup capacity of a properly sized steam boiler, so you don't need to add for that -- just size the boiler EDR to the existing steam EDR in the usual way.

    That said, though, I definitely would use a heat exchanger and two pumps. First off, I'd be uncomfortable running boiler water through the radiant piping. More to the point, though, the radiant is going to want to run somewhere around 100 F or maybe even less -- certainly not more than 120 or so -- and the water in the steam boiler is going to be a lot hotter than that! So... separate loops, and a pump on the boiler side circuit controlled by the return temperature in the radiant side, to give the radiant side a shot of heat when it needs it.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Snowmelt
    Snowmelt Member Posts: 1,415
    Thanks Jamie, I think I have a HEX left from a job that didn’t use it. If I recall there are HEX for steam am I right.