Odd Vent Hiss

RobF

Hi folks. Here's my new problem. Several minutes aFter our boiler cycles off, we'll hear one radiator hiss for quite awhile. I went and checked and the hiss is actually from the vent sucking in air. I can feel it if I put my finger over the hole in the vent. What could be causing this? The odd thing is it doesn't always happen from the same radiator.

Thanks!

wsdave

Normal

When the steam in the radiator condenses it forms a vacuum in the radiator. The vent is drawing air into the system to "break" this vacuum.

Normal operation.

HTH

Dave

Steamhead (in transit)

And

if the steam mains in the basement are not insulated, more steam will condense there and increase the depth of vacuum, increasing the hissing.

Of course those bare pipes waste a lot of fuel, too.

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Fred Harwood_2

Hissing

What king of mains vents do you have?