For years I have been reading about venting radiators slowly and have posted several times to people advising them to do so. I had been a huge fan of Gorton No. 4's and Ventrites. Very good quality vents.
I recently tried a Hoffman 1A and found it too noisy, posted the results on the forum.@acwagner
after confirming my main venting was adequate suggested bumping up my radiator venting to larger Gorton's, which to me sounded like the equivalent of turning up the pressure on the vaporstat, heresy. That being said I like to tinker so I tried it and IT WORKED!
I swapped out the Ventrites #1's and most of the Gorton No. 4's with Gorton 5's, 6's, C's and even a D a week ago and the heat is even, the radiator's are silent and, most notably, the boiler run time is shorter. Previously I could always hear a slight hiss, not a tea kettle but enough to let me know the heat was on, now all I hear is the slight click of heat expansion if that. I used the Gill/Pajek calculation, which allows for venting the run outs and bumped up when the radiator was close to the top end of the vent capacity. I am averaging about 3 minutes less run time per cycle, that's about a 12 percent reduction.
My take away is you need to vent the radiators slowly BUT if your main venting is sufficient you can vent your radiators too slowly and make your system run less efficiently.