Main Vents and Radiator Vents

AdmiralYoda

Hi guys, I'm going to try and uncap my non-vented mains and install some vents. In general, how do you size the main vents? Is too much venting a bad thing?

Main 1 has 1.312 cubic feet of piping. Main 2 has 0.750 cubic feet of piping.

Also, how does one calculate how much venting each radiator requires? I have some cheap, old adjustable vents and would like to replace them with something a bit better. Thanks!

Jamie Hall

It is very hard to overvent a main. It is possible to spend too much money, however. I would suggest a Gorton #2 on each main, though. A little pricey, but very reliable.

On the radiator vents -- once you get the mains vented, they will need to be tweaked. It's almost impossible to do a calculation on that. It's better to get some nice adjustable vents, such as VentRite, and adjust them until each radiator produces the amount of heat which you need in your specific space.

ethicalpaul

I don’t disagree with Jamie but I’m cheap so I always advise starting with a MoM #1 on each main: 

https://www.supplyhouse.com/Jacobus-Maid-O-Mist-J1-1-3-4-x-1-2-Main-Vent-Valve-3563000-p

nicholas bonham-carter

On a low pressure gauge, you can see the back-pressure or resistance of venting which should be lower than a couple of ounces, during the venting phase. Add more main venting until you get to that value. Vents are expensive, as they are an investment, paying back in reduced burner run time, and fuel consumption every cycle.
If the boiler is oversized, the pressure will rise up, after the air is out, but apart from some down-firing, there is not much that can be done about that.—NBC

AdmiralYoda

Jamie Hall said:

It's better to get some nice adjustable vents, such as VentRite, and adjust them until each radiator produces the amount of heat which you need in your specific space.

I had replaced them when we moved in, 13ish years ago. I just checked and it looks like I put VentRite Adjustable #1's in.

All of the radiators heat up as expected but I'm not opposed to buying new ones if there are better ones out there. Any fancy-shmancy adjustable ones, or just keep what I've got?

BobC

The Ventrite's are as good as it gets unless there is a radiator that is out of it's adjustment range. Don't fall for any advertisements about newer and better.