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Steam rad convert to hot water

Brad Barbeau
Brad Barbeau Member Posts: 52
I have a question about converting a steam rad to hot water.  I have two small rads that have not been tapped for bleeders.  The supply and return are on opposite sides, one at the top and one at the bottom (yes, the tops of the sections are connected).  My understanding is that the supply and return fittings on hot water rads are usually on the bottom of the rads. 

I was going to have someone drill and tap for the bleeders but was pondering last night that if I supply using the bottom and return using the top, does that not make the bleeder somewhat redundant?  My hot water heater works in a similar way, supply in the bottom and return at the top, no bleeder needed.  Of course in that case, opening a faucet lets the air out so I would need to allow for some way for air to be released from these two. 



  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    In the words of Michael Jackson...

    "Just BLEED it, just bleed it..."

    Air has a tendency to come out of suspension where its velocity is the slowest. Unless you have a fire truck for a purge cart, you will not be able to send enough water through the radiator to guarantee complete purging. With old upright cast iron radiators, you MUST fill from the bottom, and bleed from the top with NO circulators running. Hence the need for a bleed tapping. You also have a significantly higher water pressure availability to purge your water heater, and the pipes are not as large as they are in the heating system..

    This means you will be filling the radiators, supply and return lines before you enable the circulator(s). Fill from the bottom to the top, manually bleeding the top of the rad's.

    If space is limited, you can use both tappings on one side with a dip tube going in the bottom, at least 2/3's of the width of the radiator. It will look like a direct return configuration, but due to the dip tube directing the water inward, will act like a reverse return piped radiator.


    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Steamhead
    Steamhead Member Posts: 16,719
    Those rads were used on a Vapor steam system

    which does not use local air vents. That's why they weren't tapped for vents.

    I'd pressure-test these rads to at least 30 pounds before doing anything more with them, and again after making any changes, to make sure they don't leak. Use water instead of air, filling it slowly, that way if something lets go you won't have an explosion.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
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