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How many shut-off valves for hot water cast iron radiators?

housefix Member Posts: 7
I'm putting in a entirely new 2-pipe hot water heating system with cast iron radiators. Should shut-off valves for each radiator be installed on just the supply side pipe or on both the supply and return side?

What is the main the purpose of the shut-off valve(s)? i.e. is it mainly to let you turn a individual radiator on/off or control the flow? Or does it let you service/remove a single radiator without having to turn off the whole system?

The radiators will be in a rental unit. Any thoughts on if I should not install any shut-off valves at all or maybe not install the the shut-off valve in the room with the thermostat... to avoid the problem with a tenant turning off the radiator but leaving the heating system on.


  • Jamie Hall
    Jamie Hall Member Posts: 21,116
    Both where you put valves and what kind of valves you use are determined by why you are installing them -- and that is largely your decision. There isn't a "right way" to do it.

    If your objective is to adjust the flow through an individual radiator for temperature control, you only need one, and it can be either on the supply or return -- but supply seems more logical, somehow. Further, it should be a type -- such as a globe -- which is useful for throttling. If your objective is to be able to remove a single radiator for some reason, then you'd want shutoff valves -- probably ball valves -- on both the supply and return. From the heating system point of view, you really don't need any except zone or balancing valves at the manifolds.

    Turning off the radiator -- or allowing it to be turned off -- in the space with the thermostat is asking for trouble.

    For that matter, I wouldn't put valves, except possibly TRVs, on radiators in a rental unit. Too much opportunity for busy fingers...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    JUGHNE Member Posts: 10,581
    There are some hot water valves that allow adjustment but not 100% shut off. These were used in old gravity systems to insure some flow to keep the rad from freezing. If you wanted this insurance you would need at least one valve and then simple radiator 90 union. If you want 2 valves they would both have to have this feature, if you wanted it.

    Who knows what a tenant will do...maybe want the feel of camping outdoors in their bedroom...leave the window above the rad open overnight?
  • hot_rod
    hot_rod Member Posts: 19,282
    Is home run piping still an option?
    Each radiator gets a small pex S&R, valves back at the manifold for isolation. As well the ability to add TRVs to some or all of the radiators.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • housefix
    housefix Member Posts: 7
    Thank all, this is helpful information. Since this is a rental, I'll play it safe and not install any shut-off valves in the living room and bedrooms. I'll might just install a single shut-off valve in the kitchen and bathroom radiators for the tenants to adjust temperature/flow control if they wish to do so. -- since those rooms have a larger chance of being overheated.

    @hot_rod The system is a reverse return, home run is not an option.