I have a one pipe steam system that has two main supply lines going in opposite directions. I've insulated all of this piping and elbows all the way to where they enter the walls to deliver heat to the radiators. There's a smaller diameter pipe that leads in the opposite direction just below the supply main that runs to the equalizer piping. I'm assuming this is a return? This pipe is hot when the system is running. Should I insulate this piping as well? If it's what I think it is and its returning hot water to the boiler wouldn't it be worth insulating so the latent heat doesn't escape as much and the next cycle of heating up to create steam uses less energy? Thanks.

You can insulate any of the steam pipes, be it feed lines or return. Insulating the return lines might help the furnace reheat faster.

The small lines are condensate returns. They return condensed water to the boiler after the heat energy has been used. They should be insulated for energy efficiency as well as safety.

thanks for the replies it makes sense. let me follow up with a related question. one room on the 2nd floor is about 2 degrees warmer than an adjacent room with the same radiator size. what can i do to balance it out?

the reasons for the temp being warmer in one roof as compared to another is many fold. Direction of room facing sun, amount of windows in room. How well the insulation in the wall was installed etc. However to balance out the room temps with steam systems is farily easy. The air vent on the side of the radiator allows the steam to enter the radiator at a given amount. this in turns brings in more or less steam which then heats the radiator faster or slower depending on how fast the steam enters. By purchasing adjustable air vents you can balance the room by allowing more or less steam to enter the radiator.
A very good web site which explains both steam and hot water heating systems is attached.
http://www.heatinghelp.com/