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baldy Member Posts: 1
I am involved in converting an old low pressure steam heating system to hot water. The intent is to reuse the existing cast iron radiators for the heating medium. The existing control valves and traps will be removed and a air vent will be installed. There will be a new non-electric control valve and balancing valve installed on each radiator. Is it better to connect the hot water supply to the bottom of the existing radiator or the top? Should the air vent be put on the radiator on the opposite side of the supply?  Has anyone done such a conversation? If so, did you reuse the existing piping or provide new piping? How long did it take to flush out the existing cast iron radiators? At what temperature was the system set to operate, IE high side at 160 degrees? Low side at...? Was the water temperature reset based on outdoor air temperature, or did you find that keeping it at one temperature functioned better? What boiler manufacturer was chosen to be used in the system and why? I was considering a condensing type boiler with the intent of setting up the high side at 130-140 degrees and using a 30 temperature drop. Please feel free to comment and make suggestions. some of the questions contained here-in may sound stupid, but there are very few people out there any more that can talk cast iron rads, hot water heat and converting systems. Your help will be appreciated.


  • Charlie from wmass
    Charlie from wmass Member Posts: 4,322
    Tons of old posts on this,

    Do a quick wall search on converting. I had one of these jobs back in 1991 and we finished it but not what they thought they were going to save in fuel. Do they know steam can be 86% efficient and quiet? Maybe that horse has already left to barn. also Hydronic Alternatives makes a conversion valve for this type of work. http://www.hydronicalternatives.com/Steam-to-hot-water-conversion-valve.pdf
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • Rod
    Rod Posts: 2,067
    edited August 2010
    Where to Search

    Hi- As Charlie mentioned there are a lot of old posts discussing conversion. There are two search functions on this website.  You'll find one if you go the top line where the "Shop", "Ask Questions" etc. and go to the far right of the page where you will find a box labeled "Site Search" This will search articles posted by Dan on the main site. The second search function you'll find as you come on to the "Ask Questions" section. Scroll down the page and you will see an orange button marked "Search the Wall". This will search the old posts and is likely to have the info you need.

    I'm a homeowner myself and at one time was considering converting over to HW. I'm now very glad I didn't.  A couple of things to consider. Steam systems run at very low pressure (less than 2 PSI)  HW systems run at many times that so the chances of leakage using old radiators has higher probability.  A radiator operating with  steam (212+ F) puts out a lot more heat than the same radiator using HW so you may run into a situation where a radiator converted to HW is now undersized. Another thing I've noticed is a lot of the pros won't do these conversions due to a possible liability standpoint so depending on your position in this project that might be a consideration for you. The old "Wall" posts should answer most of your questions.

    - Rod
  • Jamie Hall
    Jamie Hall Member Posts: 23,438
    In general...

    Don't.  Charlie and Rod have given you lots of things to look at, so I won't reiterate -- but, in general unless there is an almost overwhelming reason to convert... don't do it!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Steamhead
    Steamhead Member Posts: 16,894
    Yet another reason not to convert

    is that a converted system would run at higher temperatures much of the time, as it tries to heat the building with its limited radiation. So a condensing boiler wouldn't condense much of the time- bye-bye, promised higher efficiency.

    Much better and more cost-effective to keep it steam and fix whatever problems it might have. Tell us more about the building and the system.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • Don't start down this road . . .

    I would not start down the road to converting an old steam system to FHW unless you are willing to replace all the piping and radiators. If your going to convert be willing to just rip EVERYTHING out and install it all new. Murphy's law has a whole section on whatever can go wrong WILL go wrong and I think he wrote it just after trying a conversion like this.

    Once you start down the conversion road you could be in for a big bag of hurt. No matter what you decide to do it will cost a pretty fair piece of change to get the heat working right. It would cost a lot less to just get a good steam man in there to fix what you have.
  • Henry
    Henry Member Posts: 998
    Steam to water

    We have done a number of steam to hot water conversion in major downtown buildings. We repipe the radiators after flushing them. Yes, it is preferable to enter by the top but, not necessary. We use a ddc to control system temperatures. proper pipe sizing will make redundant balancing valves. Thermostatic radiator valves are a good idea. The steam radiators are grossly oversized. Remember, influenza? They were sized so that one could heat with the windows open.

    A condensing boiler system is a must. A few years ago we performed this conversion for  a cathedral. Gas consumption went down 75%!

    It is so much easier to reduce energy consumption with hot water heating compared to steam.
  • Steamhead
    Steamhead Member Posts: 16,894
    In order for your numbers to mean anything

    we have to know what condition the steam system was in, what boiler was in there, etc. etc.  Otherwise the comparison is meaningless.

    I'm willing to bet there was plenty of low-hanging fruit on that system, that would have cost far less to fix than the conversion did.

    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • As Steamhead said..

    Probably lots of low hanging fruit.  To give you an example...I converted a church hot water system to a high efficiency  hot water system and cut fuel usage 75% also.  I have upgraded lots of church hot water systems and typical fuel usage reductions are 40%.    These numbers are about the same as steam to high efficiency hot water conversions, so this tells me that steam is not  inherently inefficient, but that the systems are using inherently inefficient heating plant designs and controls. 

    There was an error rendering this rich post.

  • ttekushan_3
    ttekushan_3 Member Posts: 958
    Low hanging fruit, yes

    Hi guys-

    I pick my steam heat battles carefully, so I usually get excellent results. I may have mentioned this particular case in the past but it bears repeating. Just because a steam system works doesn't mean that it isn't wasting fuel --and that it can't be quickly and competently rectified.

    A most satisfying steam job I had two years ago still pays dividends. About a half dozen contractors were asked to an open house at a very old church to look over its 1885 steam system. Most everyone who actually bid on the job quoted a complete new hot water system. One quoted a conversion to hot water with the existing cast iron radiators even though they were steam only.

    My bid was for a tune up/ descaling/ downfiring/ venting/ draft control/ zone sequencing. There were also a few errors in a partial conversion from two-pipe air vent arrangement to a vented main arrangement. However, no major equipment changes were necessary in my estimation. Consequently my bid was about 5% (not a typo) of the next bid. I absolutely guaranteed a 1/3 reduction in fuel costs. (Did I mention the system was clearly out of whack?) The result is a consistent 59% reduction in total fuel consumption per degree day. A hot water system that provides about 20% of the total heat load was untouched. Therefore, the steam system's fuel consumption was reduced more than 60%.

    The payback period was a couple months. It also appears that this congregation's board of trustees is unanimously delighted in their decision to stick with the steam system.
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