For radiators in room in which the thermostat is located; or where radiators affect operation of thermostat.
Venting capacity equal to 4. ordinary air valves. Use on radiators near boiler and in warm rooms (second-floor radiators, for example).
Venting capacity equal to 8 ordinary air valves. Use on radiators farther ,from boiler and in cold rooms.
Venting capacity equal to 15 ordinary air valves. Use on radiators farthest from boiler and in coldest rooms (for example, on third floor radiators and above).