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Air vent sizing for system with no main vent, installing 2nd vents

rca Member Posts: 11
Hi all,

Over the last couple of years I've gradually been fixing some problems with the steam heat system in my apartment. The last thing that can reasonably be fixed and that needs some work is the sizing of the air vents on the radiators. When the system turns on the sound of air being forced out of the system is very audible, and a couple of the vents whistle. The system does not have a main vent (and adding one is not an option), which is probably the most significant cause of the problem, and probably makes it more complicated to solve.

I'd appreciate if anyone could recommend a good reference with guidelines/charts/tables for determining vent size based on the volume of the system.

Also, I have a question about tapping a hole in the radiators to add a second vent. Is it OK to drill a hole directly in the column of the radiator - will that be thick enough for a vent to screw in properly? Or, is it necessary to weld in a threaded fitting? I'm curious because the existing vents appear to be screwed into fittings.




  • Big-Al_2
    Big-Al_2 Member Posts: 263
    edited September 2009

    The Heat-Timer Varivalve radiator vents are adjustable and, wide-open, are as free flowing as a Gorton #2 main vent.  You might try putting one on the radiator(s) furthest from the boiler.  They don't exactly hiss . . . more like subdued heavy breathing noises  Depending on your system, they might be more prone to spitting than a more restrictive vent  . . . but for around twenty bucks, it's a cheap thing to try.  If you can vent the whole system, then the other radiator vents will probably quiet down on their own.  I've tried the larger (size D) Gorton radiator valves, and they can make a serious racket.  I wouldn't put the Varivalves all over an apartment building, though.  The tenants would be constantly adjusting them on their own and messing up your balance.  Maid-o-Mist vents are sized like Gortons, and they have interchangeable orifices that can be swapped out or drilled bigger (up to a point) to change their venting rate without swapping the whole vent. 

    Heat-Timer has a brochure on their site that has a chart comparing their valves and others:
  • Big-Al_2
    Big-Al_2 Member Posts: 263
    edited September 2009

    Welding to a cast iron radiator will be tricky, and might just crack it.  The typical vent ports are tapped into thicker bosses cast right into the radiators.

    You could try to drill and tap a second 1/8" NPT hole in the radiator.  It's done frequently.  If I found that the section I drilled into seemed a little too thin, I'd be tempted to drill and tap it bigger, to a 1/4" NPT size, and install a 1/4"x1/8" NPT reducing bushing into the hole, with the OD and threads of the bushing liberally coated with enough JB Weld to make it look like a molded-in boss.   If you did it right, it would look like it belonged there. The bushing would become one with the radiator, and the vent would have plenty of thread depth to screw into.
  • main vent location

    why is it impossible to add a main vent? the system could burn 25% less fuel if properly maintained, which would include installing  main vents, and checking other things!

    i would be leary of drilling into radiators, unless you have had practice, especially as it sounds as though your pressure is too high! if theu are tube type radiators, the wall thinness  can make it difficult to get enough threads for a good purchase. surely there must be a way.--nbc
  • Why no Main vents?

    Hi Bob- I think you've got us all a bit confused. What exactly is it that you are having a problem with?

    The system really needs to have main vents . You mentioned an "apartment"?  Are you the landlord or a tenant?  If you're a tenant and don't have control of the system I 'd talk to the  landlord about putting in main vents as it would be an economical advantage for him at very little cost. The faster the air is removed from the mains, the faster it gets to the radiators and the room is warmed and the thermostat is satisfied and turns off the burners on the boiler.

    You don't want to try welding cast iron (old or new). It isn't really weldable. Unless you have a huge radiator you probablty don't need a second vent location.The Varivalves Al mentioned are huge!

    - Rod
  • rca
    rca Member Posts: 11
    edited September 2009

    Thanks for all the replies so far.

    To clarify, I'm a tenant in an apartment in a two-family home. My landlord used to believe that it was normal for steam heat to be noisy, and I didn't know much about steam heat when I moved in, but water-hammer can be a great motivator to learn :) I've read a couple of Dan's books and by learning enough to figure out what the problems were I was able to persuade my landlord to hire a heating pro to fix the piping that was causing the major noise problems.

    With the major problems fixed the vent noise is the last issue that needs some work (actually before the pipes were fixed the vent noise wasn't as bad because the excess water in the pipes slowed down the steam reaching the radiators) . According to Dan's books the likely root causes for vent noise problems are either that the boiler is oversized (or overfired), or the system is improperly vented. I haven't done the calculations to determine if the boiler is oversized, but my landlord wouldn't replace the boiler for this problem (especially if there are some simpler/cheaper solutions to try). Boiler size aside, the boiler is running properly, the pressuretrol is set correctly, and other than the lack of a main vent all of the piping is (now) installed properly, and the system heats adequately - these things have been checked by a heating professional.

    I realize that installing a main vent would be the best step to take but it isn't an option because the main was originally insulated with asbestos which has since been encapsulated. The encapsulation starts about 6 feet from the boiler (just after the first two run-outs) and runs all the way to the end of the main. My landlord has been great about fixing some other significant problems with the system, but asbestos related work is out of the question.

    Improving the venting at the radiators seems like the next best way to try and address the problem, and it's something my landlord and I can do on our own. I asked about tapping a hole for a 2nd vent because Dan's books suggest using two slower valves instead of a single faster valve on large radiators that are undervented.

    So, if there exist any actual guidelines or charts for figuring out venting I'd be interested to see them. Otherwise, I think I'll start by trying vari-valves on the two largest radiators.

    Thanks again,

  • venting through radiators.

    here is something you could try: temporarily replace the vent on the farthest rad with a small valve ,and compare the speed of steam arrival between the thus "open pipe" radiator vent and the present vent. don't leave the situation unattended, as the steam can remove wallpaper in a short time if unchecked! at the same time you could check the pressure with a good low pressure gauge.

    your landlord is fortunate to have such a thoughtful tenant.

    is this system a counter-flow, with the mains ending at the last radiator?--nbc
  • Main Vents

    Ideally a main vent is normally installed on each main, past the last radiator lateral at the farthest end of the main away from the boiler. They can also instead be installed on the dry return. (Think of the steam pushing the air and then think where you can put in a "exit door" to let the air out.)  The benefits (economic and from a noise standpoint) are so great I'd be still looking into this.

    NBC mentioned trying an open pipe which got me thinking. An open 1/8 inch radiator pipe has about the same air volume as a Gorton # 2 so there's a lot of vent capacity in your present radiator vent connection.   I thought that maybe before getting / trying the Varivents, if you have a spare radiator vent, another thing you might try is to make a "mini antler" and  using a 1/8 inch tee and some elbows and  connect  two vents together vent and attach that to your radiator vent pipe and see how that works out.  Just a thought.

    - Rod
  • rca
    rca Member Posts: 11
    venting the dry return

    Rod and NBC, thanks for the suggestions on venting from the last radiator. I may give that a try before the vari-valves

    Rod, I like your idea about attaching the main to the dry return - which in this system is easily accessible and not insulated, but only a 1" OD pipe. Could it cause any trouble that once the system is running there will be very wet steam going to the vent?


  • vents on dry return

    that's exactly the right place for the vent, if well protected from water-hammer. if  the near boiler piping is right, with low pressure, there should be no excessive wet steam-only condensate. the vent has a float in it to handle that. mounting on a menorah, or antler will give it extra protection against water-hammer.-nbc
  • jacksonpollack
    jacksonpollack Member Posts: 12
    Here is one solution I have used.

    I have drilled and tapped many radiators both fabricated thin pipe and cast iron of all types with not problem. Make sure your drill is sharp and your tap is sharp and held straight. Use a real tap wrench if at all possible, not a crappy adjustable wrench that lets the tap wobble all over.

     If you are not well versed in how to tap, practice on some scrap. A broken tap is a nightmare, especially if you are short on tools.

    I have also drilled and tapped the supply pipe running to the radiator before or around the valve (use some good judgment here, don't drill so close to the valve that you mess up its function), this has worked well and is more like a main vent. I have used both angle and straight vents, depends on the space. Both seem to work well.

    All this said I am a landlord, with huge, old multi-unit buildings, all steam heat. I have babied and loved these systems into quiet balance with TRV's and crazy venting everywhere and my tenants are happy and my bills are 25-50% lower for heat compared to when I bought them.

    So needless to say I would be livid if a tenant did anything other than call me if they had a heat problem.But if you have a negligent landlord than I will show you what I have given as gifts to my friends, especially those in big NYC buildings to get there heat working well for them and for my comfort when I visit them.

    Most of there places have only one radiator and a few riser pipes(which the maintance guys cutely refer to as "heat pipes") for a decent size two bedroom apt, so they are always cold.

    The photo is what I have made up and given to them. Turn the valve open when you are home and want extra heat, works great and you don't need a humidifyer in the winter. The chrome pipe can be bent to direct the steam into the middle of the room so you don't bubble the wall paint or damage anything with a direct blast of steam. Don't leave this on unattended or you will turn your place into a sauna with every peice of glass dripping with water.

    Does it screw the other tenants and cause the boiler (and landlord) numorous problems, yes. You decide your situation and if you care or feel the heating problem justifiys the karmic implications of doing something like this.
  • welcome to the greatest steam heating forum

    i would certainly like to hear more of your steam adventures/fixes, etc.

    it would give other newbies here confidence in making the old systems work! i also am in your position, however with only this 1 steam system left  [others were ripped out when we divided up the warehouses into apts.--nbc
  • jacksonpollack
    jacksonpollack Member Posts: 12
    Thank you for the welcome

    I will try to give back as much as I can. I am entirely self taught with what I have read online and through Holohan's excellent Lost Art of Steam Heating book. I learned when I had to many big bills from local HVAC guys who knew less than me about steam when I knew nothing. I hope I can cut down on some steam newbie's pain.

    I am sure you will see many of my random posts as I am once again turning on the boilers for the heating season, old stories and new rants will appear.

    I welcome everyone's criticism, please correct me if I say something stupid. Like I said self-taught and I have done and am probably still doing wrong.
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