Air Bound Steam Systems

and if they are failed closed or open and where they are in relation to other things.

i'd have to find the quite that it won't change efficiency because it can have a huge effect on efficiency. if the air can't get out the emitter will never heat no matter how long you wait. if you crank up the pressure you can sometimes compress some of that air and get a little steam in the radiator and get some heat. if it is because the trap is failed closed the radiator will fill with water and you won't even get that little bit of heat for long. as this is happening the t-stat won't satisfy and most of the heat will go up the vent and in to the basement. the boiler will cycle on the vaporstat/pressuretrol because the system can't consume all of the steam it is producing.

failed closed traps directly prevent radiators from heating. failed open traps prevent other radiators from heating by allowing steam in to the returns. this either closes the vent on the returns and prevents the radiators with good traps from venting, reaches the return on radiators with good traps and closes the trap from the return side and stops it from venting in to the return or the steam itself blocks the flow of air.

once steam starts condensing the reduction of volume pulls in more steam. the condensing steam is what causes the steam flow in both a vented and non-vented system, the vented system just gets much more surface in contact with the steam. diffusion isn't a significant factor or you would get drips filling with steam and hammering.

you really just need boyle's law, the volume change of the air due to temp isn't significant.

A radiator with a closed vent (or failed closed trap) has an interesting property: it will produce some heat, and will continue to do so so long as it is supplied with steam. t may not be all that much — as has been noted, it depends somewhat on the steam pressure — but the joker in the pack is condensation, which is, after all, what produces the heat — not the fact that the steam is hot, but that it condenses. As it condenses, the volume changes — drastically! — and more steam is allowed in, and son on.

Now in a one pipe steam radiator, that's really the end of the story — the condensate just drains out normally. In a two pipe with a failed closed trap is slightly more complex, as the condensate may — or may not — drain, depending on exactly the failure.

As t efficiency — remember that, as I have said before, it depends entirely on how you define efficiency. The factor to watch out for is where the heat is released by condensation. So long as it is released within the heated envelope of the structure, it may appear in an unwanted location, but it is not lost.

What does happen in systems which lack venting, and which can affect efficiency (or not — there are other variables) is that, assuming that the pressure controls are even remotely reasonable the boiler will cycle on pressure, even if the math shows the system EDR and the boiler EDR are close — as the unvented parts of the system will be at least partly prevented from heating, and thus will present a lower than expected EDR demand.