Watch this video from This Old House to learn how to create zones in a hot water system.
1 Turn off cold-water line to boiler; shut the electricity to boiler.
2 Drain water from boiler, if there's no floor drain remove water with electric pump.
3 Cut copper pipe coming from boiler with a tubing cutter.
4 Use reciprocating saw to cut steel pipe, remove remaining pipe with pipe wrench.
5 Thread copper adapter into boiler to connect new copper tubing; apply both pipe sealant and Teflon tape to threads of adapter.
6 Solder together new zone valve assemblies and attach to boiler with solder-less fittings.
7 Install wireless thermostat in room of new zone; locate thermostat away from direct sunlight or cold drafts, and about 60 inches above the floor.
8 Install electric control box beside boiler and make wire connections between zone valves and thermostats in each zone.
9 Turn on cold-water line and electricity to boiler.