Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

main line vents on radiators?

TonyBal_2 Member Posts: 54
Hi -

I have an odd question (I think)...I have a one-pipe system with no main line vents, and the original boiler still intact from 1930. It takes forever to heat the radiators in our house, even after I've replaced the old radiator vents on the first floor with newer, larger ones (Gorton - Models C and D, respectively). They work better now, but not as quickly as I'd like. It still takes about 25-30 minutes to complete a heating cycle.

The pipes in our basement are rather close to the ceiling, and I suspect that there isn't enough space above the pipes to tap/install main line vents on the basement pipes. (Plus, our pipes are insulated with asbestos, which I'd rather just leave alone, especially with two kids in the house) So, I was wondering if it is a good or bad idea to install main line vents on the two main radiators on the first floor of our house. I would have to build a small converter-T pipe system to change the size of the valves from 1/8" to 1/2" (to fit the main line vent onto the radiator). I can't decide if this is a good or bad idea, if I'm going to spritz myself out of existence with steam, or if this will actually work. The radiators I would put them on are very large to begin with, and are the first radiators on each of the two main lines coming off of the boiler.

Thanks much -



  • Varivalve

    OK, flame suit on . . .

    The Heat Timer Varivalve radiator vents are almost as fast as a large main vent. You could put one on the LAST radiator on each main. It's not the "correct" fix but it's easy enough to try . . . and it would look OK too.

    I don't have the headroom for a Gorton #2 main vent on my system, so I supplemented the existing, smaller main vent with the Varivalve on the last radiator . . . and it sped the whole system up.

    I'd also look for a place where the main vent might have once been installed . . . and later plugged off after it failed.
  • TonyBal_2
    TonyBal_2 Member Posts: 54
    main line vent question

    Al -

    Thanks for your post - very helpful!

    I have already looked for old main line vent plugs along the basement pipes and found none. There just weren't any main line vents installed in the original system. However, there is something odd about the boiler - there is a pipe (1/2" I think) sticking straight up out of the body of the boiler itself. It's been capped, and the pipe comes from the original pressure gauge, which no longer works. Could this be where the main line vent was first installed? Have you ever heard of a vent attached to the top of the boiler itself, instead of on the main heating pipes in the basement?



  • In order to be effective, the vents need to be as far down the main as possible. That way the steam will push the air ahead of it and out the vent. As soon as the steam hits the vent, it should close.

    Vents on the individual radiators are opposite the inlet valve for the same reason.

    Venting a radiator really quickly like I suggested MIGHT lead to some spitting or extra venting noise, so venting the main is preferable. It probably won't be a problem, though, so it would be worth a shot. If the vent drips at all, you can always dial back the venting rate with the little slider on the port of the vent.

    My $.02
  • TonyBal_2
    TonyBal_2 Member Posts: 54

    Thanks, Al! Much appreciated!
This discussion has been closed.