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Used cast iron vs. new panel radiators - efficiency/lifespan

JanelleT Member Posts: 4
It's our first winter in our 1940s house, and we suspect that our hot water heating system wasn't properly maintained - 3 of our 9 cast iron radiators have sprung leaks. We've been told that sludge/corrosion is likely the issue, but that doing a flush would likely do more damage to the already-weakened radiators. We replaced one leaking unit with a used radiator from a local vintage shop, and the other two we capped off for now.

To avoid future leaks, we are considering replacing all of our radiators with European-style panel radiators. We like the look, the fact that they are wall-mounted, and the ability to control each unit with TRVs. We've been looking at Myson and similar brands.

But... I'm worried about the lifespan and efficiency of panel radiators as compared to cast iron - for example if panel radiators would cool off faster and make our boiler fire more often, or don't have the same 100+ year lifespan of cast iron. It's hard to find a comparison online between cast iron vs. panel radiators beyond looks.

We don't want to switch away from cast iron and then regret it in higher heating bills or needing replacement radiators in a few years. The vintage shop in town has tons more cast iron units, so we could just swap those in as our system continues to spring leaks. Thanks for any thoughts!


  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,578
    It’s not just the potential for leakage in the comparison between panel rads and cast iron-it’s the thermal mass of the cast iron, which makes them superior in some ways.
    What sort of boiler is there in the system?
    I wonder if the system had a partial freeze up before you bought it, or if there could be an overpressure problem.
    You will need to have new valves with the replacement radiators, in order for the valve and spud to be matched, unless the original valve is still on the replacement radiator.—NBC
  • psb75
    psb75 Member Posts: 845
    Cast iron radiators are superior heat emitters. Its quite an advantage to have a source of replacement c.i. rads nearby. Panel radiators are a close second as heat emitters. But there are many other issues to consider: how are the current cast iron rads. plumbed? In series--I would presume. Large piping? Could you replumb with smaller pex and homerun manifold? Could you install a new mod/con boiler? Mod/cons love high mass heat emitters. But they also love (demand) good water quality.
    Panel rads. have a certain convenience in their ease of handling, installation and control once installed. Lifespan basically dependent on system water quality. Cast iron is less susceptible--due to its metal thickness and high mass.
    Cast iron is harder to work with--its HEAVY. It has vintage look, and classic function. Panel rads are "spiffy" and function really well. Material costs are equivalent. Labor costs are where the differences will really show.
  • JanelleT
    JanelleT Member Posts: 4
    Thanks - our boiler is an old cast iron model, which will likely also need replacing in the next couple years. We have a monoflow system with galvanized pipes and have been told it's in good shape. We'd want to leave the main pipes in place if possible, though we know we'd need new connections and valves.

    When we had the one radiator replaced it was fairly significant in labor costs, hence our thought that replacing them all at once with new models (and being able to flush the sludge out the system etc) would be more cost-effective in the long-term. None of our radiators have shutoffs, so every time we replace/cap off one we have to drain down the whole system.

    Further complicating things is that the majority of our current radiators are Sunrad-style, so the supply and return pipes are closer together than they would be on a more standard model (since they run from the interior of the radiator and face outward, rather than coming to the radiator through the outside edge - not sure if that makes sense). We can't find the Sunrads at our vintage shop, so replacing them with traditional cast iron radiators means re-routing pipes anyway, or having a radiator that's too small for the room.

    A mess!
  • hot_rod
    hot_rod Member Posts: 22,256
    It would be tough to guess the conditions inside your current radiators. If some have failed due to corrosion or sludge it may be safe to assume the rest are in the same condition.

    There are plenty of pros and cons between the two styles. Cast iron provide comfort, mass and a certain nostalgia to your home.

    Panels are quicker responding, take less room and would come with some warranty.
    Water quality has a lot to do with the life expectancy of any hydronic component.

    Properly installed and controlled withe will provide efficient and comfortable heat at about the same efficiency.

    I would suggest performing load calculation for the home, room by room. Determine how much heat emitter each room requires and determine what size radiators would be needed.

    It may be possible to mix and match some cast iron and panels, with proper controls and piping.

    With panel radiators it is common to design around much lower supply temperatures. If and when you upgrade the boiler a high efficiency mod con matches up with low temperature radiators nicely.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • NY_Rob
    NY_Rob Member Posts: 1,370
    If you do decide to go w/panel rads, size them for 130F Average Water Temp so they will be right-sized when you replace your cast iron with a mod-con in the future.
    If you size them for your current 170F AWT, they will be seriously undersized for a mod-con.
  • Dave in QCA
    Dave in QCA Member Posts: 1,786
    It is extremely rare for radiators on a hot water system to rust out and start leaking. I suspect "sludge" is the result of trying to explain something for which the answer is not known.

    I think a past freeze up is more likely. I have seem radiators that were in a house in which many were lost due to freezing, but somehow escaped destruction during the freeze-up. However, they were apparently damaged to some degree and were weakened or received a hairline crack which did not leak for a few years. Then, suddenly, for no explanation, the radiator that seemed perfectly fine starting leaking.

    If you could figure out how to get it done, I would replace with cast iron to match the size of the originals. Doing it all at once might be the best idea.
    Dave in Quad Cities, America
    Weil-McLain 680 with Riello 2-stage burner, December 2012. Firing rate=375MBH Low, 690MBH Hi.
    System = Early Dunham 2-pipe Vacuo-Vapor (inlet and outlet both at bottom of radiators) Traps are Dunham #2 rebuilt w. Barnes-Jones Cage Units, Dunham-Bush 1E, Mepco 1E, and Armstrong TS-2. All valves haveTunstall orifices sized at 8 oz.
    Current connected load EDR= 1,259 sq ft, Original system EDR = 2,100 sq ft Vaporstat, 13 oz cutout, 4 oz cutin - Temp. control Tekmar 279.
  • Steamhead
    Steamhead Member Posts: 16,893
    Sunrad-type radiators are available from OCS Industries:

    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • mikeg2015
    mikeg2015 Member Posts: 1,194
    Panels with their low mass work better with a mod con boiler where you keep them warm all the time but lower temps in mild weather. Cast iron is best for on/off operation since it stores heat better. Plus a lot more water volume. Water store more energy than metal per lb.
  • Paul Pollets
    Paul Pollets Member Posts: 3,656
    Panel rads require a 2 pipe system to work best and all of the radiators would require a repipe to hook up the panel rads. Sometimes it means the flooring around the radiators needs removal to do the repipe. I agree that the panels should be sized for 140 degree design to work at lower temps.
  • Mike Cascio
    Mike Cascio Member Posts: 143
    Keep the sunrads, besides you can still get new ones. Also, what pressure is your system running at? How many stories is the home? If the pressure is unnecessarily high that may amplify this problem.
  • JanelleT
    JanelleT Member Posts: 4
    Thanks all for weighing in - we got a couple quotes back for upgrading to panel radiators and they were all at least 3x more expensive than we had guessed they would be, so we will be sticking with the cast iron ones!
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,578
    Don’t forget to add in the new valves you will need.—NBC
  • New England SteamWorks
    New England SteamWorks Member Posts: 1,520
    I'm with @Dave in QCA . Not normal at all for radiators to fail. Your multiple failures means something very unusual happened, or is going on.

    Replace with what you love. Life is short.

    And btw, if you find an old cast iron radiator and have it professionally sandblasted and painted, -it will be every bit as beautiful as those new panel radiators, -and for less money.
    New England SteamWorks
    Service, Installation, & Restoration of Steam Heating Systems
  • JanelleT
    JanelleT Member Posts: 4
    As to the cause of the leaks... It's possible there was a freeze last winter, as the house was unoccupied for a span before we bought it and the heat was off. The first leak happened about a month after we turned the heat on for the first time, and the other two were a couple months after that, after we replaced a circulator pump that had stopped circulating (sigh... previous owners had a lot of deferred maintenance). We thought maybe the new pump stirred up some residual issues in the system.

    Unfortunately our pressure gauge also seems to be broken (did I mention we're replacing the boiler as soon as we can afford it?), but we turn off the system and check the bleed valves on both levels every once in a while to make sure the water is at a trickle vs. shooting out and it's seemed fine.
  • Mike Cascio
    Mike Cascio Member Posts: 143
    You should replace the pressure gauge. Its a $30 part and it will tell you what your system is doing. Higher than normal pressure will make matters worse.