Do I Use a Hoffman 75 or 4A?

[Deleted User]

Thanks! It is a 4 inch pipe 17' long. I called Hoffman and they said that the 4A and 75 are nearly identical. That's confusing advice.

[Deleted User]

Do I use a hoffman 75 or 4a?

I have an 80 year old house that uses single pipe steam heat. Low pressure at 0.5 psi. The main vent air valve was clogged, so I researched on the net for a replacement. The Hoffman 75 had good write-ups, so I bought it but have yet to install it. It is much larger than the VERY old one in there now. About twice the size. This vent has about 4 radiators connected to it, two of which are on the second floor.

I then poked around on the net and found on the Hoffman site a #4a for small or residential systems. Should I have bought the 4a instead? And, will the 75 not work as well as the 4a? I can return the 75.

Thanks, Mike

thfurnitureguy_4

Mike the way find out the size of vents needed is determined by the diameter of your steam main pipe, and the length of this pipe between the boiler and the vent. There are guys here that can help once you give this info. best of luck.

thfurnitureguy_4

Mike with any luck Steamhead will respond. He is one of the vent wizzards on the wall. Faster is usually better with main vents.

[Deleted User]

Thanks again! I called Hoffman again and they suggested that it might actually be better to use the larger #75 because, as you point out, it will vent much faster. This actually might be a solution to the slow to move steam in my other main. The air valve is good, but it takes too long for the steam to make it through. I'll check the postings. Otherwise, I will try it tonight and let you know.

Bob W._3

You have almost 1.5 cu. ft. of air in your main. That would take a Gorton No. 2 or 2 - Hoffman 75's to vent at 2 oz. pressure. I don't believe the 4A's will vent anywhere near that much. I replaced my old 4A's with Gortons.