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Cast Iron Baseboard Pressure Testing

FormerlyFormerly Member Posts: 78
Hello All,

I have some CI baseboard that I am installing, being reused from another location. I am re-assembling sections that were broken apart into sections for transport and will simply clean up the nipples, add some dope and re-combine the sections. My plan is to plug up the sections and pressure them to around 15lbs and see how long they can hold (air). My question is:

Is this sufficient? If there's a slow leak, would it be fine if over 8+ hours? Should I test with a higher pressure? Looking for some experience on what is acceptable or a red flag - thanks all!!


  • Big Ed_4Big Ed_4 Member Posts: 1,341
    I would charge with water , something you can see .. Or air and a good gauge. The most pressure it would see is 30#.
    I have enough experience to know , that I dont know it all
  • FormerlyFormerly Member Posts: 78
    I'd do water but these things are 16ft long and heavy.... using air I had one that dropped from 15lb to 14lb over the course of maybe 12 -14 hours... I felt that was acceptable.

    I have another that is losing pressure faster, I'm wrenching the fittings tighter and rechecking every so often. hoping it's not the nipples and just one of my plugs
  • mattmia2mattmia2 Member Posts: 1,297
    I would get it leak free. you will likely see a spot turn crusty with minerals from the water seeping out from the slow leak. I would give it another couple hours to a day to make sure it isn't just expansion and contraction with temp changes.
  • Jamie HallJamie Hall Member Posts: 12,847
    Water. And I'd go to 30 psi, which is your pressure relief valve setting.

    Air is tricky to test with, as you must take into account temperature changes which can either obscure leaks or make you think you have one when you don't.
    Br. Jamie, osb

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

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • FormerlyFormerly Member Posts: 78
    I didn't think about air temp variables. Thanks! I have to figure out how to maneuver these giants to test with water.... I may just test them in place and then use the manifold to suck out the water with a vac if one fails.
  • mattmia2mattmia2 Member Posts: 1,297
    You could leave the air on there for a few days. If it falls and rises again, no leak. if if falls more and more over time, it is leaking. More pressure makes a leak easier to find, but it could also make something fail that otherwise wouldn't have. With piping it is easy since it is usually rated for well over 100 psig, with a radiator you could cause a failure that otherwise wouldn't have existed.

    You can fill it with water and see where it seeps out, but with the slow leak and the greater viscosity of water there might not be much water to find. You could brush or spray soapy water on it and look for the slowly growing bubble but make sure you rinse it off because the soap will rust the cast iron.
  • Big Ed_4Big Ed_4 Member Posts: 1,341
    The low pressure test dropped , you have a leak . Try 30# with water on dry surface to find the leak..

    I would recommend new if you asked
    I have enough experience to know , that I dont know it all
  • FormerlyFormerly Member Posts: 78
    I think I found the leak on that one rad - the new bleeder valve I installed wasn't screwed down as hard as I thought...

    Unfortunately for me, due to the weight of the rads and other factors, I can basically only test them in place. It's not a big deal, I have them on their own manifold so I can purge them out without draining the whole system. I'll pressure up this zone with water to #30 and report back findings for posterity.

    I'd love to do new rads (probably would do baserays or maybe runtals) but the cost wasn't in the cards for me this time.
  • kcoppkcopp Member Posts: 3,497
    You will not be disappointed w/ the heat that cast iron baseboard puts out....
  • dopey27177dopey27177 Member Posts: 298
    remember air is compressible, water is not. Test with water, if you get a leak it would show.

    Me I would test to 30 PSIG. That would allow you to know if you use it on a water heating system (boilers usually have a 30 psi safety valve, that the cast iron base board is safe to use in the event of boiler pressure creep.

  • MikeL_2MikeL_2 Member Posts: 255
    We like to test our assembled cast iron baseboard with air using a pressure gauge that has a 30lb max dial reading. Pump the air pressure to just over the 30lb line; the lower max pressure gauge will register a leak more quickly than a 100lb gauge. Be careful while handling the baseboard; carry it the same way it mounts to the wall. Also watch out for small drips of condensation or leftover water. We once left a trail of black droplets on a carpeted stairway......
  • EdTheHeaterManEdTheHeaterMan Member Posts: 572
    I thought the industry standard for hydrostatic pressure testing is 1.5 times the maximum working pressure rating for hot water and 45psi for low pressure steam systems. I may be mistaken.
  • FormerlyFormerly Member Posts: 78
    Update Time.

    I have 4 rads and three are pressurized at 30-35 PSIG water. No leaks for 4 hours and counting. I had one spectacularly fail however - as I was flushing it, it began to spray out of a large crack near the supply intake. It did not look like this before the water test. This is also the radiator that did the best on the air pressure test by the way - interesting how it failed HARD. This means I have to find a new left end 2 foot section. Of course it's on the longest radiator, at 14 feet long. I had a bit of a panic moment seeing the water on my brand new oak floor I put down...thankfully I had 2 shop vacs ready...

  • kcoppkcopp Member Posts: 3,497
    edited June 25
    Go easy putting in the radiator spuds. Looks like you got a bit eager...
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