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Not bad. I still think you are still overlooking the importance of the different function of the vents allowing steam to get to the radiators and the vents controlling the radiator output, however.

If the runouts to the various radiators are relatively short, then there will probably be very little to be gained in terms of speed of delivery to the radiators, and indeed only large systems need vents on these runouts (or in a tall building, on the tops of the risers). In that situation, the radiator/outlet vents perform the dual function of venting the runout (minor) and controlling the heat output and hence system balance (primary function).

Now you theorize that if you tripled the venting on the radiators they would heat faster and be as balanced or unbalanced as before.

If by "heat faster" you mean that steam would arrive at them faster that may — or may not — be the case. Beyond a certain point, however, increased venting — main or radiator — may not make any significant difference at all. There are two factors involved here.

The first is that when the boiler first starts to make steam at the beginning of a cycle the pressure at the boiler is extremely low and the flow velocity off the air is, thus, also low — and largely controlled by the pressure drop in the piping unless the venting is extremely restricted.

The second is actually more important: as I mentioned earlier, the steam is condensing in the main (or runout) as it tries to heat the main up. This is influenced most by the weight (physical weight) of the mains and the insulation around them. I honestly have never run through the math on this, but it is my experience that a maximum apparent velocity of around 20 feet per minute is to be expected for an insulated main or runout, and half that — or less — for an uninsulated one (I have observed an extreme case of a two inch, uninsulated main in an uninsulated crawl space which had an apparent velocity of around one foot per minute…).

It is interesting to note that during the warmup, the steam is moving in the warm portion of the pipe at a considerable velocity — but the air in the cooler portion of the pipe is still very very close to atmospheric pressure and hardly moving at all.

On the balance of the system. Increasing the venting proportionally on all radiators — tripling, for instance, as you suggest — may or may not affect the balance of the system, but as a generalization it will. This is because there are three major factors in determining system balance: the maximum power output of the various radiators, which is controlled entirely by their size (the "EDR") and does not vary; the rate at which the radiator reaches that capacity, the length of the boiler run cycles, and the interval between boiler run cycles. It is quite rare — it does happen — for most of the heating needs for all the radiators, or even the majority of them, to reach their full capacity in any one run cycle. This is true even for systems which have been carefully designed to match the available radiator output to the required space heating needs, and even then only under more extreme conditions. Further, it is also the case that for most normal heating needs the various radiators will need to provide varying amounts of their possible output; for example, a radiator which is three times as large as is needed for a space on a certain day will need to be limited to a third of its capacity, which a radiator which is only half again as large as the requirement would need to reach about two thirds of its capacity.

Now. What governs the capacity of any given radiator? Two factors: the vent size, which controls the rate at which air leaves the radiator and thus how fast steam can reach all parts of the radiator, and the boiler cycle length which, in combination with the venting rate, will determine whether a given radiator reaches full capacity — if indeed it ever does.

Now if you increase the venting rate on all the radiators on a previously balanced system, it is quite likely that some of the radiators which did not previously reach full capacity will now do so — and the system will be out of balance.

Sorry for the dissertation, but I have the impression that you are really interested in the actual physics and dynamics of your steam system — and it's not quite as simple as it might look at first glance.