I read in your book - hissing sound can be decreased or eliminated

Natasha

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I have a one-pipe steam heat in my 2-family house (2 floors with

two separate boilers for each unit). Each has only one vent right next to its

boiler in the basement. I wonder 1) where, 2) how many, and 3) what kind

of vents should I add to the main pipe in the basement to eliminate the hissing

sound of the radiators upstairs. Please advise. I will post pictures of my main

vents for each boiler tonight.







My plumber says that HISSING is normal.

World Plumber

Pressure

What' is the pressuretrole set at? 

Big-Al_2

Hissing Normal?

I also read that radiator vents should be silent, and it drove me nuts for the first three heating seasons in my house.  I an attempt to stop the hissing of my vents, I set the Pressuretrol as low as it would work and installed a couple hundred dollars worth of main vents.  No big improvement.  The radiator vents never made any noise until the main vents were closed anyway.  



Some vents seem to make noise even at very low pressure.  If your boiler is sized "just big enough" so that the radiators fill with steam very, very slowly, then the venting will be pretty quiet.  If your boiler is somewhat oversized, like mine, then steam fills the system so quickly that the radiator vents are bound to hiss. No amount of main venting will cure that.



Turning the boiler pressure down to under two pounds is a good idea.  Lower pressure than that is better, but depending on how long your boiler takes to re-ignite after the burner shuts off and the pressure drops, you may not be able to turn the pressure down all that much.  My boiler seems to work best from 1/2 to 2 pounds.  Below that, it cycles off and on way too much and goes into vacuum every time the burner turns off.  Others here might say I have it set too high, but that's the lowest pressure that seems to work and it's consistent with what the boiler manual says . . ..

Natasha

RE: Hissing Normal? RE: Pressure

The pressure on both boilers for the first and second floor is :

main=2 psi , diff=1 psi

"Some vents seem to make noise even at very low pressure. "



Page 22 in the book "We Got Steam Heat' explains that when you raise the pressure on your steam boiler, the steam goes slower, NOT FASTER! Of course, everybody is favoring faster speed, but in my house I think over sized boiler could be a reason of the hissing. The house is not that big. I am planning to install additional main vets. Pictures are still to come.

AlexR

when do they hiss?

When do the radiator vents hiss?  Do they hiss when the boiler starts up (when steam is first entering the pipes and radiators) or do they hiss after the boiler's been running for a while and the radiators are hot most/all of the way across?



The vents on my system make a very soft hiss (that I can only hear when the house is completely quiet) when the system first starts.  If you have enough main venting you can't do much more about this.



Some of my vents also hiss later, when the radiators are hot and the pressure starts to rise.  The pressuretrol setting helps here- lower pressure will make for quieter vents. Ideally they shouldn't hiss because they're closed and no air can get out.  However, I find that some of mine don't close well when the steam is wet.  A dirty boiler with lots of gunk and oil in the water can cause wet steam (this is fixable with flushing or skimming) as can bad piping (which is harder to fix).

FJL

Vacuum

What, if anything, can be done to prevent the system from going into vacuum and sucking in air each time the boiler cycles off or shuts down? I assume this isn't god for the system, right? But so many her advocate low pressure. Lowering the pressure to 8oz has reduced my hissing issue. They hiss less than they did before, but they still hiss.

Natasha

A follow -up

The hissing starts at the beginning of  each heating cycle.

Each floor of the two-family is about 1200 sf. Each floor has only 8 radiators. The only main vent for the first floor is Vent-Rite #1933. The only main vent for the second floor is Vent-Rite #35.  Would you recommend upgrading to bigger vents ? Would you recommend adding more vents, and if so, where?

Both main vents are properly installed  at the end of the dry return for each boiler.

Jamie Hall

Nothing

this is perfectly normal for a steam system, and the air getting in never hurt anything.

Natasha

RE: when do they hiss?

They hiss when the boiler starts up (when steam is first entering the pipes and radiators).  I lowered the pressure today and will see what happens.

I am confused though, according to steam experts, lowering the boiler pressure increases the steam speed, which means the steam pushes the air out even faster, therefore the vents should be hissing even louder.Am I right?

BobC

vents

What kind of radiator vents are you using?



I've noticed the chinese vents sold in the big box stores (USAV 884 stamped on them) are A LOT noiser than the Gortons or Hoffmans. If you rap on the noisy vent sometimes they will finally close and stay quiet -for at least that cycle. And even with the good vents you do occasionally get one that is noisy, I swapped a noisy vent in the dining room withn the quiet one in the bathroom and peace was restored.Bob

Big-Al_2

Not Faster on Start-Up

Low pressure steam does move faster than high pressure steam . . . in a system that's already full of steam.  The "pounds per hour" of steam traveling down a given pipe would be about the same in both circumstances, but since the molecules of low pressure steam are less packed together (dense) they take up more space in the pipe and move faster.  But again, that's for a steam system that's already full of steam.



The Pressuretrol is just a high pressure limit switch.  It doesn't force the boiler to make pressure.  The boiler just makes steam.  Only when the boiler is making more steam than the system is condensing does pressure start to build.   The Pressuretrol just turns the burner off when steam pressure reaches the cut-out pressure and allows it to come back on when the pressure is below the cut-in pressure. 



Early in the the cycle, the boiler starts steaming . . . a little at first . . . and gradually builds up to the maximum boil . . . just like a pot on a stove.  The first steam out of the boiler only travels a short distance before it hits a cold pipe and condenses.  The pipe near the boiler starts to heat up and the steam starts finding its way further down the main pipe, pushing air out ahead of it.  At this point, the pressure in the boiler is barely above zero.  By the time the main is full and the main vents close, the boiler is steaming pretty strong . . . but the steam is still condensing faster than it's made, so the pressure stays just above zero no matter what the Pressuretrol is set at.  (If the main venting is deficient, then the radiator vents have to let out all the air, and they might make some noise.) 



Now the radiators start to fill with steam, and at first the cold radiators condense the steam faster than the boiler makes it . . . but the boiler starts catching up as the radiators heat up, and the radiators fill with steam and vent out the air. 



If the boiler is perfectly sized, the radiators will condense every ounce of steam that the boiler produces, and the system pressure will never climb more than the couple of ounces of pressure that it takes to move steam to the radiators.  The vents will be very quiet.



If the boiler is oversized, then the radiators won't keep up, and the pressure in the system builds until the limit switch (pressuretrol) starts cycling the burner off and on to limit the pressure.  If it is oversized, then the radiators also fill more quickly in the first place, especially the last ones to fill.  The vents will hiss.  If the radiators fill too quickly, some steam also can get ahead of the air and close the vents early.  The air eventually makes it to the vents and they open and close a few more times . . . now with the boiler actually making pressure . . . and the vents are even louder.



There's not much you can do about an oversized boiler except to live with it or replace it.  Some can be "downfired" . . . having the burner turned down . . . but that's fairly limited.



Does this help?

FJL

Brands that hiss ...

I have Gorton's on my rads, and nearly all of them hiss to some degree, even the "straight up" Gorton's atttached to my TRVs.  The "regular" air vents that attached directly to the rad sometimes will stop  hissing if, as described above, I tap them hard a few times.  But even that is only temporary.  Someone has suggested boiling them in vinegar to clean them out or spaying some wd40 to make it easier for the vent to close.  I haven't tried either.

Big-Al_2

Maid-O-Mist

The Maid-O-Mist vents I have seem to be the quietest, and I've tried a bunch.  I have also heard good things about Vent-Rite vents, but they are expensive and hard to find.



Yes, the generic offshore radiator vents (like the ones sold by Watts) seem to be noisy, especially when the boiler shuts off and the system goes into vacuum and sucks air back in.  Then, they actually sound like little whistles.

Natasha

Re: Not Faster on Start-Up

Thank you very much Big-Al,



As I understood, the speed of the steam that is trying to reach cold radiators in the beginning of the heating cycle is irrelevant to the boiler's pressure. Boiler's pressure simply prevents the explosion of the pipes, basically by turning the boiler off when the steam pressure in the entire system is too high (set pressure on the pressuretrol).



The amount of the steam produced by the boiler per hour can be two much for a system, this is what you call an over-sized boiler. The more steam is produced per hour the faster it is reaching the radiators in the same system. So you are saying the one who buys a new boiler should think about its size and the system it will be heating. How to find out, where to read, what size of the boiler is needed for a specific system, the system I have in my house, for example?



I closed 3 radiators on the top floor and replaced them with hot water radiators because I was adding hot water heating system for my house addtiton. As I understand, It will only descreased my steam system in size now and my big boiler will be heating smaller system pretty fast and hissing sound most likely will not be possible to eliminate.



I decreased the pressure from 2psi to 1psi last night and the hissing became less noisy, but still noisy. I am thinking to replace the main vents in the basement. Perhaps, I should start a new thread with mesurements of my main pipe to ask for a recommendation to replace my main vents.

nicholas bonham-carter

is hissing normal?

there is a choice for the air to make as the steam pressure is rising in the boiler. either it can all leave through the constipated little radiator air vents, or it can escape through generously sized main air vents. likewise, when the burner stops, and the vacuum forms all through the system, the air needs a way to reenter.

the fuel company would prefer you to have no main vents, so that you can burn more of their product!

the ease of air escape from the mains is indicated by the back-pressure in the system as it is first steaming. my system of 6 inch mains seems to let the air out at a back-pressure of 2 ounces on my gaugestore.com 0-15 ounce gauge. then as the main vents close the pressure will go up to the high limit of about 10 ounces. no hissing on the vacuum side either.--nbc

Natasha

Vent_rite#1 vents are on my radiators











On the image in this reply is the vent I have installed on

every radiator in my house (vent-rite#1). When I bought cheap vents for $7 at a

local True Value store, they were whistling as tea kettle, so loud we could not

sleep, it was a nightmare.

Natasha

Vent-Rite#1

See my reply down the thread. But they are still hissing. My  last solution would be to replace main vents in the basement.  I am not replacing my boiler to a smaller one.

Big-Al_2

Later in the Cycle

NBC, even generously sized main vents stop venting after they close.  Then the radiator vents take over no matter what.  I could add another four Hoffman 75s to my system in addition to the four I have there already, and it wouldn't quiet down the radiator vents at all.



When the system goes into vacuum, whatever vent opens first will be where the air comes in.  That's probably going to be on the coldest radiator, rather than at a main vent.  I've tried adding a vacuum breaker on the main to take care of the problem, but Hoffman/ITT units dont open soon enough and the Watts units don't close reliably.  I've heard of people using regular horizontal swing check valves as vacuum breakers, but they aren't actually steam-rated and I don't trust them for that job.

FJL

Lowest Cut Out?

How low can one go in cut out pressure?  I see yours is 10 oz.  Mine is set at 8 oz.  Is that too low? 



And does no hissing on the vacuum side mean that you do no hear a sucking sound when the boiler turns off?

Big-Al_2

Cycling

I think how low you can go on the pressure limit depends on the boiler.  If the cut-in pressure is too low, then the burner might not come back on soon enough to stop the system from going into vacuum.  Depending on how oversized your boiler is, the differential (or cut-out pressure) can be as low as you'd like.  It's just a matter of how fast you want the boiler to cycle. If the boiler is sized just right, then the settings on the Pressuretrol are irrelevant, because the system won't build much pressure to begin with. 



I keep my oversized boiler at .5 PSI and 2 PSI.  Even at that big span, on a long run when coming back from a deep setback, it cycles off and on every few minutes on pressure.  With a Vaporstat, I could have that thing cycling twice a minute or more, and that wouldn't be a good thing at all.  Maybe next year I'll add a couple more radiators in rooms that have none, and my short-cycling problem will go away.



I don't like to see the system go into vacuum when it cycles off the pressure limit.  If the vents re-open and the system is already hot, then they can start venting really fast and hiss because pressure builds so quickly.

SBoston

Heat Timer

I have replaced a lot of my vents with Heat Timer Varivalves and had good luck with them (not with their customer service).  You need to have very dry steam and are can spit water if you vent to quickly.  I have found that closing the valve all the way, still lets out enough air to vent the radiator at a good pace but not fast enough to cause spitting. In the end, this give me a super quite vent that doesn't spit water.  Again dry steam is the key to these vents working.

nicholas bonham-carter

is my system silent?

either i am going deaf [possible], or the size of my system makes it quieter [also possible].

before the new boiler, with no proper pressure control, and really bad venting, the hoffman radiator vents were hissy-whistly. with the new boiler, and useless pressuretrol [straight out of the box!], and 6 new hoffman 75 main vents, it was the same, even with the new vaporstat.

however, with first 12 and then an additional 6 gorton # 2's, the sound of venting has decreased to the point of complete silence, and we have some pretty tall risers here with our ceiling heights of almost 14 feet on the ground floor and about 11 feet on the second. maybe it's only my ground floor which has this silent advantage. there is a downside, as i now do not know when the burner is on, without looking at my radiator pressure gauge, or on the thermostat.--nbc