I have a friend who takes great pride in the fact that his crew uses 1/2" pipe in his residential installations because it shows how knowledgeable they are. At the supply houses it seems like almost nobody uses 1/2" pipe anymore. They put the valve in the middle of the zone and use only 3/4" pipe (around here we normally use 1" valves in residential). Other than a slight cost difference (we install a 7 zone system on average so the difference I think is about $30) is there any reason to use 1/2" and if that's the case why not just stick with 1" and be really simple? Sure would keep the parts simple.