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cast iron radiant?

Tim Gardner
Tim Gardner Member Posts: 183
Which brings me back to the original idea. Is there any steam design that might work for radiant? How about 2-1" steam pipes instead of the 2"? How about dropping it 3 inches below the floor? Or is it just plain a bad idea and steam is just too hot at any pipe size?


  • Tim Gardner
    Tim Gardner Member Posts: 183
    can I fabricate an underfloor cast iron radiator

    I took out a radiator on my first floor under a dining room window that will become a door to a deck, but now my dining room is a bit cold. Access to the dining room floor from underneath in the unfinished basement is easy.

    Using the condensate from my steam boiler for radiant is one good option.

    But I had another idea after seeing Michael DiMenna's clever fabricated radiator:


    What about running 2" cast iron pipes off the main between the joists, connecting the far ends with 3/4" through the joists, and then putting a 1/8" vent at the end of the 3.4", and then covering it with insulation below. Cast iron radiant heat! Ignoring time and the cost of the big iron, is this a bad idea?
  • Joe_13
    Joe_13 Member Posts: 201
    Toast your wooden floors

    Not only would you have hot spots but I'm sure that much heat cannot be good for a floor. You'd probably get splitting and discoloration.
  • Tim Gardner
    Tim Gardner Member Posts: 183

    Thanks for answering. So I gather that the reason radiant works is that the heat is spread out over a greater area? Or is radiant a bad idea for hardwood floors in general?
  • heretic
    heretic Member Posts: 159
    Low temp

    The answer is A.
    It's the low temp over a large area.
    Designed properly, there is not a problem with radiant under wood floors.
  • heretic
    heretic Member Posts: 159

    You could 'leech' some hot water off the steam boiler, and run underfloor tubing.
    Try this:
  • Tim Gardner
    Tim Gardner Member Posts: 183

    Yes, I understand that using the condensate is a good idea, as I said in my original post. But I wanted to explore the steam idea. If it could be done, it would avoid a pump, extra complexity, etc.
  • Mark J Strawcutter
    Mark J Strawcutter Member Posts: 625
    too hot

    the point is, steam is too hot. Cool enough for radiant under wood and it's no longer steam.

  • Uni R
    Uni R Member Posts: 663

    This may cost way more than it would be worth but if you could just have cast iron plates up between the joists, big buffer and no hot spots. Your house better be well built... L
  • Tim Gardner
    Tim Gardner Member Posts: 183
    how hot can the hardwood get

    in a typical radiant floor application?

  • Tim Gardner
    Tim Gardner Member Posts: 183

    I don't think hanging all that weight would help the structure any, but I am curious whether something like that could work.
  • tombig
    tombig Member Posts: 291
    Floor Convector

    Tim, your first idea isn't bad but you'll need a grille in the floor in front of the new door. They make convectors for hot water systems... 8-10" wide by 6-8-10 ft. long. Cut the floor, drop it in and pipe it. You could build your own with a steam emitter below if you have the clearance to the main for pitch, vent, etc.
    Don't try to heat "through" the floor with steam, too hot and will toast your floor. You need the linear grille. Make sure to consider convective air movement. Hot air won't rise if there's no cool air to replace it.
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