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Two valves on each radiator?

Wonky Member Posts: 10
Large 100 year old colonial. Hadn’t used the steam in over 10 years. Just replaced ancient oil fired boiler with Independence gas fired unit just as the weather got cold. Also had thermostatic valves placed on nearly all radiators (about 20–it’s a big house). So far things are working quite well. Heat is very even and comfortable and the system is quiet. My question is about the valves.

I understand how the metal cylinder on the top works: I can move the little brass pin to control the speed at which the air is bled out of the radiator and thus control how fast the unit warms up. This allows me to boost the heat in some rooms and back off in others even with a single thermostat for the house. So far, so good. But what is the plastic grey knob for? That has plus and minus direction markings and can screw tighter and looser. But what is it for?


  • BobC
    BobC Member Posts: 5,479
    edited November 2019
    The grey knob is a thermostat that will shut off when it senses enough heat. You can adjust the point at which it stops the steam by adjusting that knob.

    BTW those air vents can be a problem on steam because they vent very fast. With venting you have to find a balance between all the vents so rooms heat at the same rate. If it's all working leave it be but if it's not you may need slower vents.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Wonky
    Wonky Member Posts: 10
    I don’t understand why I have both. Do they do different things? Should I be using one instead of the other?
  • acwagner
    acwagner Member Posts: 505
    The silver one is required to make the radiator function properly. It allows the air inside the system to escape but prevents steam from being released.

    The grey one is optional, and generally considered an upgrade. It reacts to the room temperature. If the room is warmer than a set point, it prevents the radiator from heating up and overheating the room. If the room is cooler than the setpoint, then it allows the radiator to heat up and warm the room.

    They are handy to have in areas of the house that can vary in temperature from the rest of the house--such as a kitchen with the oven on all day or a room that gets lots of sun compared to other sections of the home.
    Burnham IN5PVNI Boiler, Single Pipe with 290 EDR
    18 Ounce per Square Inch Gauge
    Time Delay Relay in Series with Thermostat
    Operating Pressure 0.3-0.5 Ounce per Square Inch

  • mikeg2015
    mikeg2015 Member Posts: 1,194
    Wonky said:

    I don’t understand why I have both. Do they do different things? Should I be using one instead of the other?

    Just to clarify further. The radiator heats by steam pushing out the air when the boiler makes steam. How fast the steam enters the radiator depends on how fast the air is allowed to escape. The grey know controls a valve that opens and closes based on room temperature. The metallic vent, sets the rate that air escapes when the valve is open.

    All the radiators impact each other however is terms of balance.

    Imagine you have 12 shot glasses on a bar and you are filling them with whiskey. Since you cannot change boiler output, it’s like the bottle of whiskey has to remain at hte same angle and you can only move your arm the same speed. If you decide to not fill one glass, the others will have to get filled faster. the vent on the radiators is like determining the diameter of the whiskey glass the radiator size is like the height of the glass.

  • Gordo
    Gordo Member Posts: 857
    @Wonky : It looks to me like that grey knob on that TRV body in your photo is just a hand knob and not a proper sensing element. It looks like you need a Danfoss direct mount TRV.

    I would also consider replacing the vent with something other than Heat Timer, as they can be problematic for several reasons.
    All Steamed Up, Inc.
    "Reducing our country's energy consumption, one system at a time"
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Baltimore, MD (USA) and consulting anywhere.
  • Bill_17
    Bill_17 Member Posts: 68
    Gordo is correct, the grey knob is the shipping protection and can serve as a temporary manual adjustment cover. It should be replaced by a thermostatic operator (control) so it can automatically control the radiator's venting of air based on the ambient temp versus the thermostat's temp setting. Below set point, it then will allow the radiator to vent and steam will enter the radiator. If the room is above set point the thermostatic radiator valve will be closed and the radiator will not vent, preventing steam from entering the radiator.