The Wall
Forum / Strictly Steam / Converting Steam Radiators to HW is Condensing Boiler Worth it?
  • Post a Reply to this Thread

    Converting Steam Radiators to HW is Condensing Boiler Worth it? (4 Posts)

  • TeriD TeriD @ 8:10 PM
    Contact this user

    Converting Steam Radiators to HW is Condensing Boiler Worth it?

    I've been receiving conflicting information from a few folks re: the best options for heating our home. 
    THE BASICS:
    1) We have recently purchased 1930 Tudor home in Newton, MA
    2) We have a 2 pipe steam system
    3) Furnace is about 15-20 yrs old and from what we have been told, it was never installed correctly, so the condensate is not flowing down the 2nd pipe, it is traveling down the first pipe. -- the cost to fix this is nearly the same as to swap it out for a different heat altogether, so we are looking at our options.
    4) We are planning an analysis of our existing radiators to determine that they could #1 be converted to HW, and 2 woudl provide enough heat for the home with a HW system.
    5) The house is just over 4100 sq ft - 1st, 2nd and 3rd floors -- and has a finished basement about 1000 more aq feet.
    5) We currently have some baseboard in our master closet/bath and we have a heat pump off an old AC compressor in our family room (which needs to be replaced -- currently looking at a mitsubishi or fujitsu ductless for this application)

    What I am having trouble understanding is whether or not (due to the fact that we have steam radiators) the hot water would have to be heated above 140 degrees to make the radiators hot enough to throw heat.  If so, it seems to me that a condensing boiler would rarely run in its condensing mode and therefore we'd rarely see the 95% efficient capabilities of the boiler. 

    My questions are: (provided the analysis of our radiators shows that we can convert and get enough heat)

    1) is the hot water temp requirement in converted steam radiators higher than a traditional/standard hot water system?
    2) would you expect to see the boiler run in non-condensing mode for the bulk of the winter?
    3) would you recommend a different style of boiler to do this in our house.

    We are also installing a Unico Hi Velocity AC system - we have the option of using hydro air in some of the floors of the house -- we are fans of radiated heat (not forced hot air) so we have not thought hydro air is an option, btu I'd love to get opinions on this.

    If anyone can provide some insight to these questions, I'd greatly appreciate it.  I've gotten conflicting info from folks -- but I do find that very few folks truly know steam systems.... and it's the steam guy (who I really htink knows his stuff) who's told me that a condensing boiler would be a bad choice.

    thanks

    Teri D
  • Steamhead Steamhead @ 8:46 PM
    Contact this user

    Steam guy is right

    besides the question of whether the radiators are big enough to work with hot-water, and how hot you'd have to run them if they were (did they do a heat-loss calculation?), there is also the very real possibility that the higher operating pressures would cause leaks. I've seen where this has happened and it's not pretty.

    Hot-water needs at least 10 times as much pressure as steam, in order to get the water up to the top floor. A 2-story house needs 12 PSI, and with three floors you need 18 PSI or so. Steam can circulate on ounces, and should never get over 2 PSI.

    Do your radiators have two pipes connected to each one, or just one? If the latter, you probably have a Vapor system, which was the Cadillac of heating in its day and is still one of the best out there. Straightening it out will be money well spent. It might even be possible to extend it to the addition, bringing better comfort to that area.
    "Reducing our country's energy consumption, one system at a time"

    Steam, Vapor & Hot-Water Heating Specialists

    Oil & Gas Burner Service

    Baltimore, MD (USA) and consulting anywhere.
  • Paul48 Paul48 @ 9:07 PM
    Contact this user

    ?

    "the cost to fix this is nearly the same as to swap it out for a different heat altogether"
    What did the "Steam Guy" say the problems were?
  • Jamie Hall Jamie Hall @ 9:07 PM
    Contact this user

    This is a pretty common topic

    here on the wall -- look around and you will find some other threads on the subject.  However, in some ways that makes it easier to write about.

    In general, we do not recommend attempting to change a steam system into a hot water system, although in some situations it has been done, and in a few situations it has been reasonably successful.  It has been our general experience that it doesn't pay, even when it can be done.

    To look at your message... my comments are in italics.

    1) We have recently purchased 1930 Tudor home in Newton, MA
    2) We have a 2 pipe steam system
    These are excellent, and very easy to maintain, although it may take some minor work to restore to proper condition.

    3) Furnace is about 15-20 yrs old and from what we have been told, it was never installed correctly, so the condensate is not flowing down the 2nd pipe, it is traveling down the first pipe. -- the cost to fix this is nearly the same as to swap it out for a different heat altogether, so we are looking at our options.
    Three things here.  First, it is quite possible that it wasn't installed correctly.  This happens more than one would like to think.  Due, I think, to the inability of the installers to read directions.  However, the cost to fix it shouldn't be even close to swapping out to a different form of heat -- my guess would be an order of magnitude less.  Something is seriously wrong with that estimate.  That said, however, it is quite likely that a 15 to 20 year old boiler may have given you what it can, and it may be time to replace it.  I wouldn't care to say without looking at it.  Even so, a steam boiler, properly installed, is no more expensive than a hot water boiler, also properly installed.

    4) We are planning an analysis of our existing radiators to determine that they could #1 be converted to HW, and 2 woudl provide enough heat for the home with a HW system.
    It should be possible to convert radiators from that era to hot water.  All that is needed is to change the valves (steam valves and hot water valves are not the same) and to remove the fittings on the outlets and replace them with plain elbows.  This must be done on every radiator.  As to whether the heat output will be adequate.  The heat output of a radiator on hot water will be somewhere from half to two thirds as great as it would be on steam.  You will need to do a complete heat loss analysis of the house to determine whether this would be adequate; it won't be unless the house has been heavily insulated and draught stopped.

    5) The house is just over 4100 sq ft - 1st, 2nd and 3rd floors -- and has a finished basement about 1000 more aq feet.
    5) We currently have some baseboard in our master closet/bath and we have a heat pump off an old AC compressor in our family room (which needs to be replaced -- currently looking at a mitsubishi or fujitsu ductless for this application)

    What I am having trouble understanding is whether or not (due to the fact that we have steam radiators) the hot water would have to be heated above 140 degrees to make the radiators hot enough to throw heat. If so, it seems to me that a condensing boiler would rarely run in its condensing mode and therefore we'd rarely see the 95% efficient capabilities of the boiler.
    It is very likely that the hot water would have to run well above 140 to get adequate heat.  As you note, this means that you would very rarely see the 95% claimed efficiency.  As a matter of fact, it has been our general practical experience that even in condensing mode these boilers will not operate in real world conditions much above 92%; the claimed figures, like the optimistic figures for gas mileage on cars, are pretty much fiction.  in comparison, a new steam boiler will run around 85% efficiency or slightly better in the real world, and a mod-con hot water will be just about the same unless you can always run it condensing -- which is doubtful.  You will save very little money on fuel costs, if any.
     

    My questions are: (provided the analysis of our radiators shows that we can convert and get enough heat)

    1) is the hot water temp requirement in converted steam radiators higher than a traditional/standard hot water system?
    As noted above, in general, yes.

    2) would you expect to see the boiler run in non-condensing mode for the bulk of the winter?
    Yes, it would be non-condensing much of the time, particularly on colder days.

    3) would you recommend a different style of boiler to do this in our house.
    Indeed.  I would strongly recommend that you find a good steam man and have two things done: examine the existing boiler and determine if it needs to be replaced.  If so, have that done (it won't cost you any more than a hot water boiler would); if not, have the near boiler piping brought up to the manufacturer's recommendations.  Second, have the same good steam man make sure that all the traps and vents and other applicances on the system are present and working as they should, and adjust the pressure of the boiler (new or old) to what it should be -- less than 1.5 psi.  All this activity will cost you less than attempting to convert your steam system -- which provides very even, comfortable, economical heat when properly maintained -- into a hot water system -- and will cost little if anything more to run than a hot water system would.

    You neglect to mention in your questions a couple of other considerations about changing from steam to hot water: first, you are likely to find that radiators which are fine on steam leak when used with hot water; they would need to be replaced.  Second, you should realise that it will be necessary to remove much of the steam piping and replace it with new hot water piping, as it is highly unlikely that the steam piping is arranged in a way that is suitable for hot water.

    Good luck.


    Jamie

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-McClain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  •  
Post a Reply to this Thread