how many Taco .9A zone valves can one 24 volt 40VA transformer supply? My heating system is oil, hot water. with programable thermostats. One floor house with two zones for heat and one zone for a hot water tank. Currently there are two transformers (24volt 40VA each) wired in parallel (40VA+40VA=??80?VA) that feed the current system.

I want to wire the basement... the house had heat installed in the basement before i bought it but it was never finished, the wiring was not done. All zone valves are Taco .9A I just want to wire a thermostat and the zone valve can two transformers hold up to 4 zones? Any help on where and what knind of wire to get THANKS