Do I have the right main vent?

kfeels

Noticed that my main vent was cracked and steam was coming out the side so I went to replace the current Durst A883 3/4" which lasted only 2years, with a new one.



Went to supply house and was given a Vent-rite #57 3/4" and I installed it right away with no problem to warm the house back up.  In reading the box, I became concerned that I may have the wrong vent because on the box chart the #57 is for Unit Heaters with operating pressure of 20 PSI.



The chart lists other models for main vents (#35, #75, #77) with operating pressure from 3.5 to 5 psi and I am questioning whether I have the correct size main vent.



Is this 20 PSI too much for a main vent?

BobC

Don't know, more info needed

Main vents are sized by the amount of air contained in a steam main, that air should be allowed to escape quickly. How long is your steam main and what size pipe is it?



Bob

kfeels

Pipe size

The pipe is 2in diameter.



What should I measure for length of steam main?

BobC

Approx length

All of your radiators should feed off the 2" main, just give us the approximate length of each of your mains.



Bob

kfeels

measuring mains

I measure 50ft of steam mains

BobC

Bigger - much bigger

That works out to about 1.1 cu ft of air and the vent you now have is much to small to handle that. I would suggest you start with a Gorton #2 and you may have to add more to get optimum venting.



The Gorton #2 is a large vent (7 to 8" tall), make sure you have headroom for them. f your existing vent is 3/4" thread you will need a 3/4 to 1/2 adapter because the Gorton has a 1/2" male thread.



Bob

kfeels

high pressure problem

Thanks Bob.  I will measure to see if there is enough headroom for these vents.  I noticed I have another main vent on a smaller return pipe 1/2 inch in diameter.  The vent looks very old and is similar in size to radiator vent at 1/8 inch opening.  If I replace this 2nd main vent, what vent size do you recommend?



Also, since I installed the new vent-rite main vent, I have experienced the sound and sight of the furnace blowing steam out the safety valve.  This concerns me and a look at the pressure guage shows 10 psi which is much higher than needed.  I ran downstairs to watch the steam blowing out of the safety valve and it lasted 60 seconds.  Only 13 minutes later the safety valve blew steam again so I turned off the switch at the furnace.



Any advice what I can do before calling a professional?

Steamhead

Call a pro NOW

your system is over-pressurizing. Try the Find a Contractor page of this site. 

Hap_Hazzard

+1

The number of things that would have to be wrong with a domestic steam heating system to allow it to develop 20 psi of pressure is staggering.

BobC

Not safe

Steam boilers use a pressuretrol to limit how high the pressure can get and are usually set for 1.5PSI. It sounds like the pipe between your boiler and that pressuretrol is blocked and the pressuretrol has no idea of what the pressure is.



The pressuretrol has to be removed and checked; the pipe 9called a pigtail because of the shape)has to be removed and cleaned or replaced.



You must not operate that boiler till this is fixed.





The shorter main would use a proportionate air valve as the long main needs. Is the current vent tapping in the side of the pipe or is it a bossed down fitting at the end of the main?



Bob

Hap_Hazzard

Safety

It sounds like his safety valve might not even be working. It should have popped at 15 psi, and it's up to 20. That's +33%--not just a little over--way over!



Apart from the obvious safety issues there are some long-term maintenance issues here. Franks right--he needs to call a pro.

kfeels

reverse the course

since this problem with pressure began when I replaced a main vent, I decided to take it out and put back the old vent. this will be temporary until I can get a new vent that is the right size.



So far, the pressure is good as it cycles through.



The new Vent-Rite #57 vent may have caused the pressure to rise. Looking at the table on the package, this vent was rated for operating pressure of 20 psi. There was no steam venting through it. This is the wrong vent and i will return it to the supply house and ask for another size.



Bob, on the shorter main the vent it is on the end of a corner on a fitting.

Dave in QCA

Wrong Vent

This vent is not a good vent for using as a main vent because it is a Unit Heater vent.  This type of vent has a slower venting rate than a main vent so it will not work adequalty for you.  The 20 psi rating is of no concern.  It merely indicates the maximum pressure it can be subjected without being damaged.  It does not say that it needs 20 psi, nor that it will cause the pressure to rise to 20 psi.

kfeels

Size of shorter main vent

Bob, what do you mean by "proportionate" for sizing the main vent on the shorter main?  Should I use a Gorton #2 like you recommend for the longer main or another size?



See attached picture of current main vent on shorter main

kfeels

Size of shorter main vent

Bob, what do you mean by "proportionate" for sizing the main vent on the shorter main?  Should I use a Gorton #2 like you recommend for the longer main or another size?



See attached picture of current main vent on shorter main

BobC

Ratio

If we are going to use a Gorton #2 to vent a 50ft 2" main then your shorter main will require a vent that is proportionate to the first. If it's 25 ft it will need a vent with half that capacity.



All of this is a starting point so you might have to add more venting for aptimal venting.



What have you done to defuse the bomb in your basement? If the relief vent went off it's a sign that something is seriously wrong with the pressuretrol and further operation put you and you family in serious peri.



Bobl