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A little air leaving a steam radiator is normal. Constant hissing, spitting water, or rooms that overheat while others stay cold means the venting or boiler pressure needs attention.
Steam radiators need vents to push air out so steam can enter. Once the radiator heats, the vent should close.
If it keeps hissing or spits water, the vent may be bad, the radiator may be pitched wrong, or the boiler pressure may be too high.
Replacing every vent with the fastest vent is not balancing. The right vent speed depends on radiator size, room load, and distance from the boiler.
$120-$250 typical
Old vents stick open, hiss constantly, or spit water.
$150-$450 typical
Too much pressure can force vents to hiss and fail early.
$120-$300 typical
A radiator must drain condensate back toward the valve.
$250-$800 typical
Poor main venting makes radiator vents do too much work.
Steam radiators get hot. Keep hands and children away from live vents.
Note which radiators hiss longest.
Check whether any vent spits water.
Make sure the radiator valve is fully open.
Look at whether the radiator pitches slightly toward the valve.
Lincoln Square greystones, Portage Park bungalows, and two-flats often have radiators that were changed room by room over decades.
A good repair looks at radiator vents, main vents, boiler pressure, and piping together.
If this page is close but not exactly your problem, these pages may match what you are seeing.
Brief hissing as air leaves can be normal. Constant hissing, spitting water, or loud vent noise is not.
On one-pipe steam, keep the valve fully open or fully closed. Half-closed valves can trap water and make noise.
No. Vent size should match radiator size and location in the system.
Bernie's checks vents, pressure, pitch, and main venting so radiators heat without the noise.