Sizing Hoffman steam vents

Unknown

today - part of a recent boiler install . It was one main of 3 , which ran about 25 feet and teed into a seudo 2 inch riser that went through a crawlspace to heat 5 rads on a 2 story addition . The run of this steam main tee , and the pipe that runs horizontal till it drops and becomes the return , was reduced to 1 1/4 , so we changed it to 2 inch all the way . We also replaced all the return piping and added main vents in the proper places . After letting the system steam for about 30 minutes the whole house heated evenly , except for the 3 radiators connected to the main we repiped . I pulled the vent on 1 of the rads and it heated up pretty quick .

I am looking for a chart on venting capacities for the Hoffman line . The website goes into general detail only . The home has a hodgepodge of new rad vents , mostly Hoffman 40s . Our supply company only carries Hoffman , otherwise I would give Gorton a shot .

I have a pic of the original main piping , I just cant find it . I'll try to locate it . Thanks for any help in advance .

Unknown

Some pics

The main we repiped is the lower one closer to the back wall in the boiler pic . In one of the pictures it looks like the main slopes down toward the boiler - it doesn't , it just the angle of the pipe off the wall . It had a slight pitch down toward the end of the main - not enough for my tastes , but it had some pitch . In the pic " Steam Main tee " the piping to the right of the tee is 1 1/4 , reduced from 2 inch - not so good . We repiped it to the wall in 2 inch and dropped it down a few feet in 2 inch also . The return pipes were all 1 inch and were teed in way above the new boiler's water line . We replaced it all with 1 1/4 and teed it at the floor . I shoulda took some after pics .

Steamhead

You can find the complete chart

in Dan's "Dead Men's Steam School" workbook. You're probably using the #75, it will vent about 1.4 CFM. The smaller #4A will only vent about 0.4 CFM. These values are at 2 ounces pressure.

The workbook explains how to measure the amount of air you ned to vent.

I'd double the venting capacity on the slow main, that should bring it into balance.

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Unknown

I used the 4A

main vents for those 2 side by side mains ( Why I couldn't use the 75s is another issue ) . The steam main on the other side of the house had an old Hoffman 75 though .

The 2 inch pipe carrying steam to the addition goes directly into what I called a crawlspace in the other post , which is in fact a no-space . No space in there to see exactly where it goes off to .

I could try the largest capacity vent on this problem main and smaller ones on the other 2 , but after 30 minutes and the 2nd floor bedroom rads not hot , I was thinking of trying the fastest venting Hoffmans on each rad up there first . Whaddya think ? Thanks Steamhead .

Steamhead

It would make more sense

to increase the venting capacity on the main. Larger rad vents might work, but might be tough to balance since you would be venting the main thru the rads. Get rid of the air in the main in the proper place, and when steam reaches the ends of all the mains quickly and at about the same time, balancing the rest of the system will be easy.

I almost never use those 4A vents- I think other installers use them because they only know Hoffman vents and the 4A is the cheapest one. They only have enough capacity for very short mains- under about 15 feet or so of 2-inch pipe. Most times I take them out and put in larger ones.

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Unknown

Tricky situation

Seeing how far away the outer wall is on the addition ,as a guess that 2 inch pipe going though the no-space is one long main , probably 20 feet or more . And there is no way to find where this main branches off , unless we rip up hardwood floors .

I think I'm the one going back tomorrow to make the best . We do have a few 75s in the shop . 1st thing we'll try is 2 of the 75s on the problem main and see what happens . Even with 2 slower 4As on there , all 3 mains were hot at the ends within 5 minutes . I'm thinking that the 3 rads in the homeowner's bedroom are so far away that even with the larger capacity main vents on this run , it'll still take forever to get em hot . I'll ask my supplier if they have the vent capacity chart for Hoffman . Thanks again Steamhead .

Steamhead

If those rads have very long runouts

you might want to increase the vent capacity on the long main even more, to give them a head start. Let us know how it works out.

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Unknown

I didn't go back

I had to replace a hanging GE boiler , but a serviceman buddy of mine went back . Stu changed the Hoffman 4A to a 75 on the problem main pipe and left the 4A on the 2nd main next to it . He moved that other 4A to the 3rd main on the other side of the basement . He also changed 3 rad vents in the bedroom to Hoffman 43s I believe . I hope this did the trick . We'll know by tomorrow .