cast iron radiators

Discussion in 'HVAC Heating & Cooling' started by mowin, Feb 18, 2008.

  1. mowin

    mowin New Member

    Messages:
    16
    Hello,


    Recently purchased a home for rehab that was abandoned before winter set in. As such, the boiler and bout half the radiators cracked.

    Is it possible to mix a new type steel radiator with some of the existing cast iron?

    I've been told of different heat radiation values from the cast to the steel and it wouldn't work.

    Cannot find any used cast without paying exorbinant sums.

    Thanks for any help or suggestions.
  2. BigLou

    BigLou New Member

    Messages:
    138
    mowin.
    as long as the radiator is properly sized to provide the room with the correct amount of BTU's it should not matter what its made out of

    Lou
  3. krow

    krow Plumber

    Messages:
    906
    Location:
    Ontario, Canada
    IMO, It does matter. The cast iron takes longer to heat up and it also takes longer to cool down, the steel or copper rads tend to heat up quicker, but on the down side, cool down quicker as well. If the thermostat is in an area which is being heated with cast iron rad, the rooms with the steel rads will cool down when thermostat isn't calling for heat.

    However , if you can balance the house according to the type of rad , ei; a cast iron rad valve can be closed slightly to allow the steel rads to heat up for a longer period of time, then you will be good to go.
  4. seaneys

    seaneys New Member

    Messages:
    192
    Location:
    Chicago Suburbs
    Is there any chance you could zone the two systems radiators separately if you got into trouble? It would give you a brute force way to balance the heat load if needed.
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,015
    Location:
    New England
    There are thermostatic control valves for radiators that would work fine to balance the rooms out (or at least I think you'd have a chance to do it). They go in place of a shutoff valve.
  6. mowin

    mowin New Member

    Messages:
    16
    interesting,

    Thanks folks.

    In one reply that is what I understand that if the thermo is in the cast room, the steel rad rooms will cool down to quickly.

    Dual zoning would not be practical.

    If there was a thermo on the steel rads, if the boiler was not on due to the main thermo in the cast room, it wouldn't make a difference cause heated water would not be "on" ? i.e. if the steel thermo "said" give me heat, there wouldn't be any to give cause the boiler would not be on, circulatory pump not running ?

    Thoughts?

    And P.S. If anyone knows were to purchase used cast rads w/o a second mortg. much appreciated.

    thank you!
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,015
    Location:
    New England
    You could let the circulator run, and let each room adjust it's needs based on its thermostat. These are totally mechanical, no electrical parts - they adjust the flow through the radiator to maintain the user set temperature. This also makes it easier to cool off a room that isn't being used to a predictable temperature. The boiler could be set to turn on when the return was a certain temp using aquastats, and abandon the central thermostat.
  8. Where are you located??

    Just wondering about where you are located
    and wether you have done an assessment of
    your air conditioning??

    if you got to sink a lot of money into the
    place , if everythign is frozen and
    cracked here and there
    just wondering if it would be more feasalbe
    to switch to a forced air system ??
  9. mowin

    mowin New Member

    Messages:
    16
    thanks for your posts.


    I really don't think a forced air system would work.
    The house was built in 1930's and all the outside walls are brick and masonary. No insulation. No way to insulate unless the wall were built out - inside.

    I believe a hydronic system the only way economically to supply a 'steady' heat. Forced air would be instant warm. instant cold ? I think.

    Thanks for the help.
  10. krow

    krow Plumber

    Messages:
    906
    Location:
    Ontario, Canada
    If you replace the rad in the thermostat room, then the rest of the house would use the heat in that room to turn the boiler on and off,
    If you make the rad vlave in that room work, you can adjust the amount of hot water running through the cast iron rad, allowing the steel rads to heat up longer. The rest of the house's heat would be gorverned by the room temperature of the thermostat location.


    I find that you can usually pick up cast iron rads at a salvage yard (scrap metal dump) at a fraction of the price of new ones. Of course you will have to pressure test them . Some places will sell them by the pound . Scrap dealers usually offer about 3 cents per pound and you may end up picking one up for 5-20cents per pound from them (depending how desperate you look)
  11. Wet_Boots

    Wet_Boots Sprinkler Guy

    Messages:
    798
    Location:
    Metro NYC
    You can probably get better efficiency with a new forced-air furnace than a boiler would provide. There are multi-stage furnaces that will run for longer intervals, as they adjust the BTU input according to heating requirements. I have a project where steam heat may be replaced with forced air, for lower operating costs, not to mention central air.
  12. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,015
    Location:
    New England
    It depends on the price point you are trying to end up with, but a two stage furnace with a variable speed fan would allow the system to run at low temp for a long time, keeping the temp even. Another thought is to use a high velocity system - the vents are very small and are designed to go in the ceiling. You'd often end up with more than one in a room depending on the size, which helps to keep temps more even.
  13. BigLou

    BigLou New Member

    Messages:
    138
    Unless I am missing something here he has a hot water system. its possible to get a hot water condsing unit thats 98% efficient. They will also modulate and provide lower btu's when needed. They are most efficient when running at low temperature for longer periods of time. It will also provide a very comfortable heat.

    Lou
  14. frenchie

    frenchie Jack of all trades

    What Lou said. Plus, hydronic heat is way, way more comfortable.

    Mowin - where are you located? In NYC, there's plumbing shops that re-fit & re-sell cast iron rads, pretty cheap. Last time I checked, a few years back, they were going about 25-50$.

    That said, I'm not understanding why you can't mix cast & steel rads on the same system. The cast rads have a built-in thermal reservoir, so to speak, so there's a lag... but if the room with the thermostat has a steel rad - what's the problem?

    As long as your replacements are sized properly, there's no reason cast and steel should/would transmit a different amount of heat per cycle. BTU's are BTU's. Am I missing something here?


    Lou - you know a lot about hydronics - any idea why it wouldn't work?
  15. krow

    krow Plumber

    Messages:
    906
    Location:
    Ontario, Canada
    I never suggested it wouldn't work. All I suggested was that the house needs to be rebalanced with the mixture of heating material elements. There are extra steps that need to be taken for the system to be balanced properly ei; the amount of heat producing water running through a particular materialed rad
  16. Wet_Boots

    Wet_Boots Sprinkler Guy

    Messages:
    798
    Location:
    Metro NYC
    Must have been the hissing of my radiators making it hard to think. I still think 'steam' when I see the word radiator, since just about nobody wants cast-iron radiators in their homes, if they have a choice. (At least I didn't include a link to the Coal Burner website)
  17. seaneys

    seaneys New Member

    Messages:
    192
    Location:
    Chicago Suburbs
    That is a great idea.

    All you need is a thermostatic valve. They even make them with remote sensors in case you have radiator covers.
  18. seaneys

    seaneys New Member

    Messages:
    192
    Location:
    Chicago Suburbs
    Wow.... For total system efficiency it is virtually impossible to beat hyrdonic heat. It is simply much more efficient to heat water and move it around than it is to create and move hot air.

    I'd stick with the hydronic heat.

    Steve
  19. seaneys

    seaneys New Member

    Messages:
    192
    Location:
    Chicago Suburbs
    The only issue I can think of is if the radiators have significantly different thermal properties. Some steel rads have very low thermal mass. They are not designed to 'store' heat. Most cast iron radiators that I have seen have large thermal masses.

    Steve
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