Noisy Air Vents on Radiators

EasilyFound_2

During this heating season, I've noticed that the air vents on the radiators in my apt make noise for part of the time that the steam enters the radiator, but more so at the start of the cycle. The pressure on the vaporstat is set at 1.5 pds with a differential of 1 pound.

I live on the seocnd floor of a four story building that has one pipe steam. We had a new boiler installed in the summer of 2007. After installing the boiler, the contractor installed all new Gorton 6 valves on the rads in my apt. The contractor also installed additional venting in the system: a triple quick vent on the main in the basement, and single quick vents on each of the five risers.

On two of the rads in my apt, the air vents will give an extra loud exhale or whoosh before the system shuts down for that cycle. I've noticed this on two of the three rads furthest from the boiler.

One of the rads that did this was a rad in my bedroom and I recently replaced the valve on that one with a Gorton C. This rad is connected to the riser that is farthest from the boiler. On Sat, a cold day, the valve seemed to have a wet sound as it vented, and I noticed a tiny, tiny amount of vapor spit out. Mostly there is no vapor and, as far as I can tell, the vent seems to work.

Last winter, the system ran at slightly less pressure, 1 pound with a differential of 7 ounces, is what I think it was. I don't seem to recall the air vents being as noisy last heating season.

Do I not have enough venting of the main and the risers? Will lessening the pressure alleviate this problem?

Brad White_203

I am thinking

that despite the best efforts, the main vents could be more generous. That is not to say that the radiator vents are off the hook, but generous main venting will give the radiator vents a lot less work to do.

FJL

True . . .

I figured someone would give me that answer. The contractor originally intended to install two triple quick vent trees on the main, but decided to install just one. I don't know why the change of mind.

Looking at my notes, I see that last heating season, we ran the system on one pound of pressure with a 12 ounce differential. Can we heat the building the same as now, but alleviate the noise by lowering the pressure to what it was last year?

We were advised to lower the pressure as a temporary, potential fix to a water hammer problem, which we have since fixed and which is why the pressure was put back to where it is now.

I don't seem to recall having this much noise during the last heating season when we ran the system on the lower pressure. But the radiator in my bedroom was turned off last year because of the water hammper problem, so maybe the system is making the same amound of noise but I'm noticing it more because the bedroom rad is a big one and now turned on.

I should add that there is also another vent on the main. Not sure of the brand, but it is a large one shaped like a bell or mushroom.

nicholas bonham-carter

steam pressure

i don't think you need the higher pressure.some old systems were designed to operate on 2 ounces!
my 60 radiator 3 floor system is heating the beginning of the radiators at 3 ounces but will go up to 8.
i also think you can never have to much venting capacity as long as the several mains are vented in an equal amount off time. naturally there is a point of diminishing returns as the venting capacity of a tree of vents may exceed the capacity of the pipe.
lower the pressure, and then try more venting--nbc

FJL

OK

I'll lower the pressure to what it was last year and see if I notice a difference.

FJL

FJL

This Morning . . .

the hissing began about 35 minutes after the boiler started running after the evening set back ended, and as the final quarter of each radiator heats up. The hissing has been quieter this morning. Mild temps this morning. About 45 degrees. T-stat satisfied in about 45 minutes, and hissing stopped. Still operating at higher pressure. Didn't get a chance to lower it yet.

FJL

I lowered the pressure

I lowered the pressure to last year's levels, and there is less noise. The valve's still hiss, but not as much and seems to be more so in mid cycle, after the rad has had a chance to heat up. When the t-stat was satisfied, and the boiler turned off, I noticed that whoosing sound in one air vent, but realized it is the sound of air being sucked into the vent. What is that about?

nicholas bonham-carter

whooshhhh

when steam condenses, it leaves behind.............nothing-a vacuum.
at the end of the cycle, the collapsing steam in the pipes and rads will leave a vacuum which then must be filled [as nature abhors a vacuum] with the air rushing back in through the vents.
this quality of steam is also the cause of water-hammer. when steam gets trapped in a pocket of water the collapse is sudden enough to accelerate the water at high speed into the end of the pipe.this is why the advice to protect the vents.
how much setback are you using? you might search on here for earlier post regarding setback.--nbc

FJL

By set back

are you talking about when the heat turns off at the evening? The setback has not kicked in yet, and this happens sometimes, not all times.

I also don't understand what you mean when you wrote "this quality of steam" that causes water hammers. I assume the sound is air from outside the rad rushing into the valve and the rad. That isn't steam, and I'm not having water hammers.

I'm very confused.