Can you have too much main venting?

chris22

I had a guy come out three days ago to look at replacing a new steam

boiler. Looks like he wants to put in a Peerless 64 model 64-07 in my

apt house. Based on measurement of 853 sq feet of radiation after

measuring the radiators. he wants to install two Hoffman main vents,

which I'm not totally happy with after reading  that most guys here like

Gorton Mains.



In the system now there are two Gortons. They are in the cellar but it

looks to me like they are not at the end of the lines. Shouldn't they be

near the returns not far from the boiler?



The system has seemed to work okay but I have no idea if it's working

okay heat and no water hammer wise, but inefficient fuelwise.



I also wonder how much is enough and can you have too much main 

venting. Should I asked for larger diameter taps in the returns so that I

might in the future if needed put what you call an antler of two or

more Gorton's ?



I know I have to walk a fine line here not to get egos involved i.e. "who's the expert here?"



Another question I have a three-year-old VXT-120 auto water feeder on

the current boiler. In his proposal I see he wants  to put a new one

on.is a three-year-old VXT-120 two old use?



As I understand it these water fillers are mainly for emergency filling,

only actuating when the low water cut off tells it that it needs water.

Is there any other good way/gizmo/control to ensure proper level as its

pretty far for me to  go out and  check it

moneypitfeeder

if you could

Please measure the size of your mains length and width, (ea) and we can see about how much venting is appropriate. Also are the main insulated?

chris22

travel

Umm, the property is 130 miles from here and I won't be able to go out for a few weeks due to other commitments.,, but I was wondering what is the hazard/problem  of more venting. Is it a thing of more isn't better? (within reason)

     

                                     

Maine Vent

Old VXT

I put my old VXT water feeder back on my new system in Nov.2011. It was on an old V7 Burnham, for about 3 years. The VXT got a workout along with the LWCO, I was going around the digital readout twice. The VXT gets to 999 and the back to 0. My old VXT is working just fine on this new system, I made sure the copper that was left on the VXT was clean, also the backflow was clean. Good luck with your new system. Your old VXT won't know that it is on a new system,compared to your old system, still a water regulator device.

Rod

Main Vents

Hi- While it is very possible to have too much venting on your radiators, it isn't likely to cause a problem on your steam mains.  You might want to take a look at Gerry Gill's Website. http://www.gwgillplumbingandheating.com/      Gerry is a Cleveland steam pro who wrote the book on venting. His website has a lot of good information on steam.  Be sure to check out the article on Maximum Venting



You mentioned having 2 Gorton main vents but didn't tell us how many steam mains you have or the size of the Gortons 

 Both Gortons and Hoffmans are very good main vents .

Venting capacity:

  3 ea Gorton #1 s =  1 ea. Gorton # 2, 

  2 ea, Hoffman # 75 = 1 ea Gorton # 2

If they are fairly long steam mains I'd put a Gorton #2 and a Hoffman #75 on an "antler" on each main.

The Gortons open and close at around 145 degrees and the Hoffmans open and close at a higher temperature.  The Gorton give you volume venting and the Hoffman closes later and opens sooner.

- Rod

nicholas bonham-carter

Capacious venting

The way I know that my 18 gorton 2's (on six dry returns) are adequate is by seeing the back-pressure of venting as the boiler is starting to make steam. I have a 0-15 ounce gauge, and vaporstat. During this venting stage, the pressure is below 1-2 ounces, showing me the lack of resistance to the escape of the air in the pipes, and boiler steam chest.

On the rads are Hoffman 40's except for the 3rd floor where I have some gorton d's. The hoffman main vent is well made, but expensive for the capacity I would need..

In your case with the property so far from you, it would be better to have more main venting than you first calculate, and verify its operation with the low-pressure gauge. The tennant or caretaker can also monitor the system in this way, as well as reading the water meter on the auto-fill. In my case, being next to the boiler, I have no aut- feed, as I feel they are a source of problems, especially for those boilers running at higher pressures.--NBC

chris22

Again, thank you

Thank you guys (also)



Rod,..Interesting about using two valves (hoffman and gorton) on the same system,..



Never occurred to me with (Nicolas's method of verifying  its operation with the low-pressure gauge.)Thank you all for your input and tips!

Charlie from wmass

Too much main venting wastes one thing

your money paying for the vents, using the tables and properly sizing the vents is the best bet for long run because as the vent wear out and need replaced you are not buying twice the venting you need. It will not cause problems for the system as long as each section is over vented to the same amount.

Dave Mc

Vent opens at too high temp.

Is there a main vent that stays closed at a lower temp than the Gorton?  Don said they open around 160 (or 145?)  I would like to find one that stays closed to a lower temp.    p.s. question  ...pressure has no effect on them opening and closing does it?  (running between .5 and 2 psi)

nicholas bonham-carter

How much is too much?

If you have a good low-pressure gauge, such as 0-3 psi, you can read the back-pressure during the venting stage. The ideal is under 2ounces. A higher pressure means that more fuel is being burned to force the air out, instead of allowing it to escape easily. If the main venting is restricted, then also the velocity of the air being forced out of the vent orifices is higher, possibly sucking up some debris and plugging the air passages up.

You can certainly estimate the number of vents you need from the size of the steam mains, and dry returns, but the final proof will be in the pressure.

Unless your pipes are small, the hoffmans will not be enough, except as additional venting.

While you are having the new gauge installed, why not put on a vaporstat to keep the pressure in the ounces.

The existing lwco should surely have a life span longer than 3 years, so I would keep it, if only as a backup 2nd means of defense against dry-firing. It should have a meter on it, and that should be monitored closely, especially during the first winter.

Presumably, the new boiler will be piped according to peerless instructions.--NBC

BobC

To much?

You can't have to much main venting but like Charlie said the venting on each main has to be balanced so steam gets to all the radiators at about the same time.



My 2" main is only about 15 ft long including the header and i use a Gorton #1 (0.33 cfm), it's more capacity than I really need but they are no more expensive than the Ventrite #35 (0.11 cfm).



Bob

Dave Mc

Vent opens at too high temp.

Is there a main vent that stays closed at a lower temp than the Gorton? Don said they open around  145 I would like to find one that stays closed to a lower temp. p.s. question ...normal pressure has no effect on them opening and closing does it? (running between .5 and 2 psi)

Is there a link anywhere with vent capacity and temp response for various make/models?

nicholas bonham-carter

venting temperatures

I'm not sure i understand your question about the opening and closing temperatures. as long as they do not allow steam to pass, then all should be well.

there is an ebook in the shop here about venting capacities, but i can't remember whether temperatures were recorded as well as venting capacity.

the most important thing to remember is the main vents must have a lower restriction than the radiator vents. this causes the mains to fill, not only quickly, but also fill before any steam begins to rise up into the radiators. when the mains are full, and the main vents close, the steam will start on its upward journey to the radiators. assuming that all the radiator vents, are the same capacity, then all the radiators on [say the 2nd floor], will get steam at the same time. in a tall building system, larger vents may be put on the top, to compensate for the tall risers.  

the usual problem in balancing systems only with radiator vents, is that the bigger vents get steam arriving first before others instead of at the same time.--nbc

Dave Mc

Here's the prob.

Thanks nbc.  The rads will reach temp and close before the thermostat is satisfied ( both floors, 11 rads ) .  The boiler will stop on pressure (about 2# I'm working on getting it lower).  The prob is- in the horribly insulated basement position the main vent cools quickly- and opens, releasing the pressure stored and cycling the boiler to re-steam only the main.  I understand the need to further reduce the pressure. Yes, the main is well insulated and so is the vent riser nipple- is's just the cold a** drafty basement location.  I'm doing ALOT of other work on the header/loop/return and suspect that will help also. But for now is there a way to find the main vent which stays closed to the lowest temp?

nicholas bonham-carter

short cycling

if you have enough main vents, the pressuretrol will not shut down on pressure before all the rads are full.  what sort of vents do you have on the rads? if you have a good gauge, then you can see what pressure your pressuretrol is shutting off at. --nbc

Dave Mc

The rads are full.

All 11 of them.  On a cold start up they reach temp long before the thermostat is satisfied.  Depending on how cold the ambint room temps are they will vary/ alternate staying closed/opening during condensation (before satisfying thermostat).  It's during THAT time that  the darn basement main vent will open- the boiler senses the need for steam......out goes the steam to heat the main vent only.  I am trying to solve this cycling problem during a COLD start. Otherwise it is pretty good, and will be getting much better soon.  I certainly do not want to slow the steam to the rads just to keep the boiler from shutting off on pressure?  The rads take awhile to bring the abbient temp up to satisfy the stat.  In the meantime the rads are well balanced and maintain a fairly even temp throughout the house.  I need to stop the main vent from dumping the steam from the entire system and cycling the boiler.  Is 145 pbobably the lowest opening temp available on a main vent?

nicholas bonham-carter

Main vent mysteries

The only way the boiler can sense the need for steam is when it receives a call from the thermostat. The switch closes, current flows; and if the lwco, and pressuretrol are within limits, then the boiler will fire. The fact of whether the main vent is open or closed will have no effect on the operation of the burner. When the burner cuts out from thermostat, pressuretrol, or lwco, the steam collapses, and a vacuum develops. The vents are designed to open to let the air back in to relieve the vacuum.

If you think the vents are opening during steaming, then there is a problem with the vents. Are the mains insulated with fiberglass?

If the system is short-cycling, even with the thermostat set up high enough to run for a long time; then check the anticipator in the thermostat, or the settings of the pressuretrol. Inadequate venting will cause the pressuretrol to shut down the system, because of high back-pressure. Then as the steam condenses, and pressure drops, starts again-very wasteful.--NBC

Dave in QCA

It may not be as it appears....

OK DaveMc, I'm going to take a stab at your problem.  If I understand what you are saying, it goes as follows.  You start your boiler on what you are calling a cold start.  I am guessing that you are either starting the boiler after it has not run for quite a while and more importantly, the space is cold, quite a bit colder than the thermostat setting.  This would be called recovering from a setback. This often requires continuous steaming for a long period of time.  So, the boiler comes on, starts to boil, steam travels out and pushes the air out through the vents.  The main vents close first, than eventually as the radiators become fully heated, they rad vents close too.  At this point, the radiators are all hot and the rate that steam is being condensed drops considerably because there is no longer any cold cast iron radiators and no cold steel pipes.  So, with the condensation rate slowed down, the boiler is producing more steam than the system can condense.  The pressure begins to climb. Assuming that the space is still below the set-point of the thermostat.... eventually the boiler will shut off when the pressure gets up to the set point of the pressure-stat or the vapor-stat, which ever you have. 

Now... Before we go on, I want to stop and talk about vents.  Most vents that I have seen, whether rad vents or main vents, will cool down after a while and they will crack open a bit until steam hits them again and then they close.  Hoffman rad vents very typically click open for a little bit, then click back closed.  The amount of steam lost s extremely small.  I have also seen this operation on Hoffman 75 main vents.  Gorton vents that I have observed seem to open a very tiny amount and make a little bit of sputtering sound.  This is probably due the fact that they function with a bimetallic coil instead of a fluid filled capsule.  While the Gorton may make a fairly good amount of sputter, the noise is caused by the fact that the port if only very very slightly opened.  As soon as the coil is heated back up it will close.  During this time, the steam lost is Extremely small.   Steam loss as a result of vents opening is NOT what causes your boiler to start back up.

Remember, when your system starts up cold, it takes a long time to heat the whole thing up because there are thousands of pounds of cold cast iron that have to be heated up.  In the process they condense a huge amount of steam.  Once the rads and piping are all hot, the rate of condensation drops... but it does not stop.  All of your radiators are still condensing a huge amount of steam.   Your rads will give off 240 BTU of every sq ft of surface area, and they will condense an amount of steam to maintain the temperature of the radiator.  Remember, it does not cool off as long as the steam is up.  But, as it is giving off heat, it is also condensing steam.. that is where the heat comes from.   So, I am guess that it is only by coincidence that you happen to hear your main steam vents crack open a tiny bit, and then in a little bit the boiler starts up again.  But, the fact is that one has nothing to do with the other. It is pretty normal, especially when coming out of a setback, that when a boiler operates in a prolonged steaming condition, the boiler will cycle off and on pressure until the thermostat is satisfied. 

My assumption are based on what I am guessing you are observing.  If, for some reason your main vents are faulty and when your they open, that they actually release a huge amount of steam... which would be evidenced by the boiler room becoming filled with a cloud of steam, then you must have some faulty vents.  But, my guess is that my earlier description is the answer. 

Dave Mc

Thanks for hanging with me nbc

1. The rads are up to temp and closed, condensing the stean as they are supposed to- all rads are full.

2. The thermostat is calling for heat because the ambient room temp hasn't satisfied it yet.

3. The boiler is holding on pressure shut off (unders 2#), waiting for one/any of the rads to condense enough steam to colapse and open it's vent for more steam.

4. While 'holding' the main vent drops below temp, opens, and releases the steam from the main. causing the boler to cycle again just to fill the main again and heat the main vent so it closes.

5. This scenerio happens during a warm up from cold (50deg stat setting changed to 70deg) from about 15-20 min- when the rads vents are first satisfied -untill the stat is satisfied, maybe an hour or so.  It may also happen during normal temp maintenance operation but it's rare because the boiler rarely shuts of on pressure.

6. The vent 'antler' is insulated up to the neck of the cheap main vent with 1' fiberglass and back the main for a few feet where it changes back to old asbestos wrapped in foil.

7. Since I'm changing the main vent, and doing some pipe work, I thought I would replace it with the vent which has the lowest re-opening temp due to the condtions in the basement.  I havn't found any mfg sites that list the temp properties of their vents, I've been searching.  I got excited when I saw Dan's post listing Gorton as 145, Hoffman higher, and was hoping someone may have additional data on temp response.

Thanx, Dave

Dave in QCA

misunderstanding

Your description of operation under item 3 is not correct.  The rad vent does not open as a result of collapsed steam.  It does not need to open to allow more steam to enter.  When the radiator is fully heated, and the steam is still up, steam is continuously flowing into the radiator, steam is being condensed, condensation is flowing out.  This flow continues without any operation of the vent.  The vent is only needed to let the air escape from the radiator during the initial heating phase.  After the rad is heated, vent cycling is only caused because the vent cools down a bit, opens, and steam quickly causes it to shut.  It is not necessary to allow steam to continue to enter.  In fact, you could do this manually.  You could put a little manual valve in the vent hole of the radiator.  you could have it in the open position when the boiler begins to operate.  You could stand there and watch and when the radiator eventually fully heats and steam begins to escape through the value you could close it.  As long as the boiler continues to fire, steam will continue to flow into the radiator to replace the steam that has condensed.  The condensate will continue to flow out of the radiator as well.  The only purpose of the vent is to let the air out.  The air only enters the system when the boiler is off long enough that the pressure drops to 0.  as the remaining steam condenses, the system goes into a slight vacuum and sucks air back into the radiators and pipes.

Dave Mc

Yep Dave

That's the deal. The steam doesn't fill the room but that's the idea.  Due to the location of the main vent it's head cools very quickly. (may's well be outside.lol).

I can't remember exactly but I believe it opened around 175 (measuring just under the insulation near the neck.)

When the anbient temp of the basement has risen also. it will open much less, or release much less before re-closing.

Any info on temp response of main vents?  Thanks for the tech term on recovering from a setback. And thanks for the explanation of continual steam processing.  I was posting again in reply to nbc, was trying how to explain the radical ventelation again.

Thanks lots,

Dave Mc

BobC

Dave Mc -20 degree setback?

1. 5. This scenerio happens during a warm up from cold (50deg stat setting
2. changed to 70deg) from about 15-20 min- when the rads vents are first
3. satisfied -untill the stat is satisfied, maybe an hour or so.  It may
4. also happen during normal temp maintenance operation but it's rare
5. because the boiler rarely shuts of on pressure.

Having a 20 degree setback for steam is pretty unusual and can cost more than it saves. Is this a situation where the building sits unoccupied for a long period of time?



I replaced my balky pressuretrol with a vaporstat a few years back so now it shuts down at 12oz of pressure. You can generate all the pressure you want but it's not a good use of fuel. I also made sure my main vent was more than large enough to get all the air out of the main as fast as possible. i also installed a programmable thermostat and use a staged 5 degree setback (8 hrs 59 - 8 hrs 63- 8 hrs 65) - some consider that 5 degrees a bit high. After all that I saw a nice reduction in oil use.



You could wrap a main vent with insulation as long as you don't do the vent hole itself, that should help solve the vent cooling you are experiencing, just make sure you keep an eye on it to make sure the insulation isn't getting wet over time.



Bob

nicholas bonham-carter

Setback recovery problems

That was a good explanation Dave QCA!

While you are waiting for the arrival of a good low-pressure gauge, try running the system with no setback at 66 degrees just to see the difference.

The gauge will tell you if your boiler is over-sized, which would account for the shutting off on pressure. If it is, it may be possible to down-fire it.

What size is your system (boiler cap. Plus rad count)?

What sort of thermostat do you have, and is it steam compatible?

What are the settings on your pressuretrol?

Is the waterline steady during the warmup?

Is your piping insulated?

My system has 55 rads, 1,050,000 btu, and operates in the 2-8 ounce range, and no more pressure is needed than that, with no setback..--NBC

Dave Mc

Thanks Guys

Great input.

Yes the boiler is oversized, I forget the exact figures but it's about 30+% after allowing for unmeasured risers etc.

I'm adding a header/dryer, Hartford, new wet returns.  This will all be a major improvement.

Using programable stat now.  When the house is occupied it will not experience a 20deg setback.  and when the heating season starts I'll be able to tweek the pressure down lower.

I dont think I can downfire this gas boiler, but am going to investigate.

Thanks.DMc



Any info on vent temp response?  Or is finding a Gorton #2 my best.

nicholas bonham-carter

Keep the old, or new boiler?

Is the present boiler leaking? Will it be replaced with one which is sized to the total radiation edr? You may be able to down-fire, but it should be done by someone with a combustion analyzer, and not by "looking at the flame color".

If there is no leaking, then it would make sense to try the down-firing, equiping the system with more main venting so the boiler doesn't shut off on high back pressure ( above 2 ounces) during the venting phase at the beginning of the firing cycle, the capacity verified by an accurate low pressure gauge.

You would learn a lot by getting the steam books from the shop here.

Good luck-NBC