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Steam/Hot water Hybrid Setup

mcs1925 Member Posts: 9
my house was originally built with steam heat which works great. The extension (comprised of a bathroom and two bedrooms) that was built in the 60’s has hot water baseboards which are connected to the same steam boiler.
The setup worked ok. The extension was never as warm as the steam heated rooms because the baseboard rooms always cooled off faster, but we lived with it.. 

The issue we came across now is we are having the bathroom redone which originally had baseboard. 

We figured it would be best to switch that to a cast iron radiator which we did. 
Now, the extension doesn’t get heat at all.
I tried to bleed the radiator but air gets sucked in like a vacuum instead of bleeding out. And I noticed any water in the baseboards and radiator now drain back into the boiler. 

Was it a mistake to switch the baseboard to a cast iron radiator? Is there a way to fix this while the bathroom is still under construction? 

Thank you in advanced for the help! 


  • Jamie Hall
    Jamie Hall Member Posts: 23,454
    May I presume that the hot water baseboards and ne radiator are higher than the boiler? If so, there is a way to do this. Presumably there is a circulating pump. Make absolutely certain that the return from the hot water system is normally connected well below the boiler water line. Now you should be able to turn on the pump and, with it, fill the baseboards and radiator with water -- open the bleeders and make sure they flow water. When a bleeder is flowing water freely, close that bleeder -- until all the bleeders are closed.

    Hopefully this will purge all or at least most of the air out.

    Now so long as you don't open a bleeder again, or the return from the system gets above the boiler water level, it should work properly.

    Check the boiler water level...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • mcs1925
    mcs1925 Member Posts: 9
    False alarm to anyone who read this thread. 

    Turns out the person who installed the radiator forgot to open the valve to the circulator pump..

    I noticed it was still shut when I went down to double check. 

    Once I opened it, the new radiator heated up faster and better than I ever imagined. 

    I’m so lucky this was an easy fix. 
    Thank you Jamie for your input! 
  • ethicalpaul
    ethicalpaul Member Posts: 5,740
    Congrats, but still, see if it will bleed air out when the pump is running (after all, you did let air in and depending on the radiator it may still be in there.

    my open system (without a heat exchanger) works great once the air is out of the loop, but my pump isn’t strong enough to get there. I have to flush the air out by hooking a hose to it from my sink.

    once the air’s all out the pump circulates it just fine
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el