Uneven Steam

Hi,



I have a 24 unit building with small apts. (efficiencies and 1br's).  Its a 1 pipe steam system fired off of oil and we can't seem to get the distribution into some of the apts at any acceptable level.  The system is old.  Every radiator in the place has had the air vents changed to heat timer vari-valves which have helped us out in the past but we just can't get the steam up in some of them without completely smoking out the rest of the building.  Can we add more main stack vents someplace to get better distribution?  What's the best move for starters?  Unfortunately, like most, we're running on a pretty tight budget at this point.



As a side note, were getting crushed on oil bills because we don't let people get cold, so we're considering a gas conversion.  Any thoughts or advice is much appreciated.