new main vent

MelroseDave

I just installed a new main vent. At the very start of the heating cycle, the rads at the beginning of the cycle hiss loudly for a few seconds.Then, it stops, and silence for the remainder of the cycle. I've already replaced the rad vents (in the vents that are hissing)  and they are completely open.

Any suggestions?

jpf321

need more info ..

What type of main vent did you install?

Did they hiss before the new main vent?

What name/model main vent did this replace? or is it a new piece on the system?

Where exactly is the main vent located?

How long is your main (from the boiler connection) to the end?

What size pipe is your main?



Those pieces of info should be able to get us started ..



I think you mean the rads closer to the boiler are hissing, not "in the cycle".

nicholas bonham-carter

newly hissing vents

in addition to jp's other questions, what is your pressure?

if your main vents are large enough for the mains, and the pressure is low enough, you will not get a hiss from the radiator vents, during steaming.

this is also true for the reverse of pressure build up, when the system goes into an intense vacuum, at burner shutdown. during that phase, the pressure differential is 14.7 to 0 psi, and a lot of air will need to rush into the pipes and boiler steam chest. if the main vents are not up to the job, then the radiator vents will hiss and sing!

this is the the time when the pressure differential is at its greatest peak, and puts the vents to their greatest test.--nbc

MelroseDave

a few answers

What type of main vent did you install? Vari Vent #77 (my plumber bought it)

Did they hiss before the new main vent?  Yes, not quite as loud but longer in duration. It is now quick but louder.

What name/model main vent did this replace? or is it a new piece on the system? The old one was replaced. It was very old, maybe original to the system (40 years or so)

Where exactly is the main vent located? It's located a few feet from boiler

How long is your main (from the boiler connection) to the end? The house is about 25 feet in lenght. so the main runs the full lenght.



What size pipe is your main? Not sure. With the old insulation encasing the pipe, if I connect my thumbs and pointer fingers and make a circle, its about that size. 





Those pieces of info should be able to get us started ..



I think you mean the rads closer to the boiler are hissing, not "in the cycle".

Exactly, it is the rad that is almost directly over the boiler. probably less than 8 feet away.



Sorry about the lack of detail....I'm very new at this.  

MelroseDave

answers

in addition to jp's other questions, what is your pressure? slightly less than 2psi



if your main vents are large enough for the mains, and the pressure is low enough, you will not get a hiss from the radiator vents, during steaming.



this is also true for the reverse of pressure build up, when the system goes into an intense vacuum, at burner shutdown. during that phase, the pressure differential is 14.7 to 0 psi, and a lot of air will need to rush into the pipes and boiler steam chest. Before I replaced the vent, I got hissing at burner shutdown, not any more, only at the beginning at the rad closest to the boiler.

if the main vents are not up to the job, then the radiator vents will hiss and sing!



this is the the time when the pressure differential is at its greatest peak, and puts the vents to their greatest test.--nbc

Rod

Main Vents

Hi-

Main Vents-  Just as a comparison, here are the venting capacities of several types of main vent.  The venting capacity of the Ventrite #77 is .190 CFM /1oz.  A Gorton #1 is .330,  a Gorton #2 is 1.00, The Hoffman 75 is .500.   As you can see with the Ventrite #77 you are on the very low end of the scale so you might want to consider increasing your venting. You could either add more vents (see attached drawing by Brad White) or change out the present main vent.  I use 3 Gorton #1s on each of my mains.You might try adding  a Gorton #1 to your presenting venting and see how that performs. Using an "antler" you can always easily add more if you want.  Gorton vents are available at Pex Supply on the internet.

- Rod

Big-Al_2

Mine Too

When my (Burnham IN-6) boiler starts up from setback, the system makes sort of a hissing sound for thirty seconds or so early on in the cycle . . . actually the sound is more like somebody turned on a faucet in a different room and you can hear it in the pipes.   The only thing I have been able to figure out is that there must be a small amount of condensation clinging inside the upper part of the boiler, above the normal water line, and that it flashes to steam very quickly when that part of the boiler first gets hot enough.  The sound goes away long before the rest of the water actually boils.



Is this kind of like what you are hearing?

MelroseDave

follow up

Follow up:

The rad that's making the noise is the one closest to the boiler. I have the vent on that rad set at the fastest vent setting. I, perhaps ignorantly, thought if air could flow out faster, there would be less friction on the airflow and therefore less hissing.

What if I were to adjust the rads closest to the boiler so that they vent more slowly. Could this reduce the hissing?