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Sizing vents with or without connected edr

2 part question!

With 2 pipe systems and no rad vents (either traps or inlet orifices)
would I size my vents on just my mains (like a 1 pipe system) or would I also include my edr connected rad load.

also with the nuisance of traps (replacing every ten years, 1 going bad-all going bad and the cost)
it seems that just removing the guts and placing orifices on the inlet would be a “no moving parts” application. 
Can an empty trap handle the condensate sufficiently?
im thinking about this at a few locations?

(cough cough) @Jamie Hall.  ??


  • Jamie Hall
    Jamie Hall Member Posts: 22,952
    Sort of in reverse order here... a radiator trap, with or without the element, can easily handle the condensate put out by a radiator. The volume isn't that great. Further, the ability of the trap to vent air out of a radiator is much greater than any common radiator vent -- and, in fact, most main vents.

    On the replace the traps every ten years. Not if they are not abused. Most of the traps on the system Cedric powers are 90 years old, and still work quite well -- including the crossovers, which really work hard. The key there is "abused". No back pressure. No overpressure. Now that said, you can reduce the load on the traps by throttling the steam coming in -- either with orifices or, on many older systems, simply partly closing the inlet valve until the radiator never -- even on the longest runs -- gets 100 percent full. That trick only works, however, if you have close control over the pressure -- but that's true of orifices, too.

    Now... sizing main vents. That depends on how your two pipe system is piped. There are two flavours: with or without crossover traps. If there are crossover traps, all the venting is being handled by the vent (or sometimes vent cluster) where the dry returns join before dropping to the boiler. In the other type, there are main vents instead of crossovers. In the latter type, you would size the main vents just for the main to which they connect. You must also vent the dry returns, however, to handle the radiator venting! This is sometimes overlooked. My own view on that (it's not easily determined by math!) is that the combined capacity of the dry return vent cluster should be comparable to the main venting. In the former type, you would size the vent or vents in the cluster to handle the mains as a group. Do you need to add in the radiator venting as well? No. The reason is this: the mains will need to be vented rapidly, which they will do through the crossovers. The radiators haven't really started yet. By the time they do -- and need venting -- the mains will be pretty well empty, and you are just venting the radiators.

    Hope this helps...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • McSteamer22
    McSteamer22 Member Posts: 23