What air vents do you have now, If you put in an adjustable one ,Dole
, the tennants will ajust them higher. Gordon makes 3 or 4 vent ranges
for controling heat You have to record all temperatures and then
balance your bldg. normaly the farthest away from the boiler has the
largest opening and the smallest is near the boiler. You havnt said
where you have to much heat, near the boiler or farthest away, You need
calibrated thermometers in every apt, or an infrared to go around to
each unit and start a log. Then you can figure your course of
adjustment