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Replacing cast iron steam rads with aluminum rads

random12345 Member Posts: 43

I'm a homeowner in the Boston area with single pipe steam heat burning oil. Theoretically for the purposes of this discussion, and assuming my system has no other problems, will replacing my 6 iron standing rads and 2 iron convectors with aluminum rads lower my oil consumption, and if so by how much? Will aluminum rads corrode? Will they cause corrosion anywhere else in my system? Water pH at the treatment plant is 9.72, at the tap its in the mid 8 range using pH test strips.

I've heard aluminum rads can lower heating bills by 5-15%, but haven't found any hard data or studies to back this up. They apparently need to use less steam due to their higher thermal conductivity, and heat up and cool down faster. I would imagine that causes the boiler to cycle on-off more frequently so possibly more wear and tear in that regard, but overall this seems like an easy way to save money. Am I missing anything? I would appreciate hearing your experiences/perspectives. Thanks.


  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,515
    Aluminum will have less thermal mass, and probably cause more cycling of the boiler, and of the money in your account.
    The cast iron is tried and true, and although more slow to heat up, (maybe), the heat released by the steam is never lost, no mater what material the rads are made of.
    Real economy can be had with low pressure, under 6 ounces, and generous main,(not rad), venting. Avoid temperature setbacks, less than 24 hours.
    If you decide to make this change, change all the radiators to avoid imbalance of various areas.—NBC
  • Jamie Hall
    Jamie Hall Member Posts: 17,190
    Replacing cast iron with aluminium -- even if you can find aluminium radiators suitable for steam -- will cause you nothing but trouble. As @nicholas bonham-carter said, you will lose all the slow release characteristics of the cast iron, and the thermostat will cycle more often and the boiler cycle more often.

    It will not save fuel -- that's controlled by the heat loss of the structure -- although it might actually use a little more, due to the increased cycling.

    Not sure where you got the "info" that aluminium radiators will lower heating bills by 5 to 15%, but it's somebody with a very weak grasp of physics...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,515
    Maybe this theory comes from a comparison of the boiler heat exchanger materials, rather than the radiator materials.
    There are no aluminum steam boilers, only hot water. If we compare a mod-con water boiler with aluminum heat exchanger with a cast iron water boiler, there can be some improvement in efficiency, as long as the capacity of the radiation is large enough to keep the loop temperature low.—NBC
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 2,437
    edited April 24
    There is no science that backs up the theory of aluminum radiation makes emitting heat any more efficient than any other metal. At least not enough to save 15% on operating cost. I believe that NBC has an insight as to the savings of aluminum over cast iron. You can't make a cast-iron condensing boiler (you could but it won't last a year before the condensation rots it away). So you can't compare a cast iron condensing boiler to an aluminum condensing boiler. You can only compare a cast iron non-condensing boiler to an aluminum condensing boiler. The metal does not make the boiler more efficient, the condensing feature makes the boiler more efficient.

    You are comparing the difference base on the wrong parameter. The metal is not the thing that s more efficient. If you were able to find an aluminum steam radiator, then went to the expense of installing them on your existing steam system, You would be disappointed with the results of your project. All that expense, and no measurable savings.

    I Vote for trying it anyway and let us know how that works out. Keep accurate expense and fuel usage records so we can all learn from others' mistakes. This sounds like a good project for a government-funded study at a major technical university. We spend taxpayer money on far more ridiculous studies.


    Edward Young
    Retired HVAC Contractor from So. Jersey Shore.
    Cleaned & services first oil heating system at age 16
  • random12345
    random12345 Member Posts: 43
    edited April 25
    Ok. Thank you for your comments. So my mistake, the radiators are actually not pure aluminum, they are bimetallic, steel core and aluminum body apparently. Made by Sira in Italy. Still waiting to hear back from their sales rep. Seem popular in Europe. Several Italian companies in that market. Russians too.

    House was built in 1938. Boiler is 25 years old. I'm still investigating what we need to do. The boiler has consumed 432 gallons of freshwater in the last 3 years according to the automatic water feeder, so we're talking with a contractor about that...However it gets resolved, I was thinking about making the system as efficient as possible by turning it into a vacuum steam system and using these bimetallic radiators.
  • Jamie Hall
    Jamie Hall Member Posts: 17,190
    432 gallons of water in three years? Forget playing with the radiators. Find your leaks. I regard Cedric as thirsty -- and he's taken a grand total of 3 gallons of water (exclusive of LWCO blowdowns) over the winter.

    You may have a boiler leak, or a several leaks out in the piping -- wet returns are notorious for that.

    I might add -- if you have leaks at all, you'll never hold enough vacuum to do any good other than waste your money. Vacuum systems have to be tight.

    I have looked closely at the Sira Industrie web site. I regret to say that while they do seem to have a nice line in hot water heating radiators -- though I personally wouldn't pay the premium price -- I find no reference to their being used on steam heating systems, or being usable for steam heating systems, nor that they have designed for use with or tested with steam.

    Therefore, I cannot urge you strongly enough to get, if you choose to use these radiators, a statement in writing and witnessed, from the installer, the wholesaler, and the manufacturer that they are suitable for use with low pressure steam heat, and also what either the EDR (Effective Direct Radiation) for each radiator is or, failing that, what the actual BTUh output of each radiator is when fed with low pressure steam. You also should get a guarantee, similarly in writing and witnessed, from all three that they will reimburse you for all costs and will reinstall your old system to your satisfaction should they fail to operate satisfactorily on steam.

    I might repeat my previous comment -- they will make no improvement in your heating system's efficiency and they may actually make it slightly worse.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • random12345
    random12345 Member Posts: 43
    Thank you for your advice Mr. Hall. Those are all good suggestions. I have yet to speak with the Sira sales rep, so it's still early days.
  • mattmia2
    mattmia2 Member Posts: 4,016
    You need ti figure out where that water is going or all that fresh water will kill your boiler (if it hasn't already).
  • ethicalpaul
    ethicalpaul Member Posts: 3,141
    If you want to lower your bills and still have a boiler that will last 30 years with proper care, keep your steam system but get a gas hookup instead of that oil. As has already said by people much more experienced than I, don't worry about the radiators, there is no loss there.
    1 pipe Peerless 63-03L in Cedar Grove, NJ, coal > oil > NG