Heating systems that feature boilers and radiators can be hot water or steam systems. Hot water systems heat rooms by pumping hot water through the radiator, where the heat is radiated out into the room before the water flows back to the boiler. Hot water systems always have two pipes attached to the radiator, one at each end near the bottom.
Radiators for steam systems look similar to hot water radiators, but they operate through the flow of gaseous steam vapor rather than hot water. Radiators for these systems may use one pipe or two pipes. If your steam system uses a one-pipe system, the radiators will be mounted with air vents that need to be periodically cleaned.
How Single-Pipe Steam Systems Work
In the two-pipe steam system, there is one network of pipes that distribute steam outward from the boiler to the radiators, and separate pipes that collect the condensed steam as it turns back to water. In a single-pipe system, however, a single pipe both delivers steam outward to the radiator and collects the moisture that condenses and transports it back to the boiler. The single-pipe system depends on special one-way radiator vents that close when they heat up, ensuring that steam doesn't escape. But when the system cools, the vents must open up to allow free passage of air.
The air vents on radiators for a single-pipe system are usually bullet-shaped devices, pointed on one end. The air vent is located on the opposite side of the radiator from the control valve, which has a twist knob. In single-pipe systems, there is very often a characteristic hissing sound caused by air passing through the air vent. This hissing sound will occur as the system is just beginning to heat up, as well as when the system is cooling down.
During the system's heating cycle, the heat-sensitive air vent closes to contain the steam inside the system and prevent it from escaping into the room. At the beginning of the heating cycle, air within the radiator will escape through the vent, often with the characteristic hissing sound. Then, once the vent senses the high temperature as steam fills the radiator, it closes tightly to contain the steam. As the system cools down again and moisture condenses, the air vent opens again to allow room air back into the system.
Occasionally the air vent may clog with rust or mineral deposits. Sometimes a troublesome radiator air valve must be replaced, but in many instances, a simple cleaning will restore it to working order, as described in the following steps.
Equipment / Tools
- Open-end wrench
- Small pot
- Plumber's Pipe Seal Tape
- Household white vinegar
- New air vent (if needed)
Turn Off the Radiator
Turn off the steam to the radiator by closing the supply valve found on the end of the radiator opposite the air vent. If there is no valve, turn the thermostat to a low setting to ensure the system is not producing steam while you work.
Remove the Air Vent
Using an open-end wrench, remove the air vent from the radiator by turning it in a counter-clockwise direction.
Clean the Vent
Heat a small pot of household white vinegar and submerge the air vent in the hot vinegar. Let it soak for about 30 minutes, allowing the vinegar to dissolve any mineral deposits and loosen any rust. Rinse the vent with cold water.
Test for free airflow by blowing through the vent. If you cannot blow through the air vent, then repeat the process again. If you still cannot blow through the vent, then it needs to be replaced with a new one.
Reinstall the Vent
Reinstall the cleaned vent (or new one) in the radiator by wrapping three loops of plumber's pipe-seal tape around the threads in a clockwise direction, then screwing the vent into the radiator vent fitting until it is hand tight. Tighten an additional one-quarter turn with a wrench. Adjust the head of the vent so the pointed end is facing upward.
Test the Vent
Reopen the steam supply valve on the radiator and test the operation of the vent. The vent should allow air to pass through as steam begins filling the radiator, but then should close to retain the steam as the system gets hot. As the system cools, the heat-sensitive vent should open again to allow air back into the system. If the vent does not close as the system heats up and open as the system cools, then the vent fitting needs to be replaced.