I am a do it yourself kind of guy, who has a few questions.
We have an old house with a hot water heat system. It is two zones system with a 2" feed and return for both floors. Off the feed and return is a 3/4" pipe that runs to each cast iron radiator. We want to put a thermostat in each room and replace the network of pipes that we have in the basement with a manifold pex system. Am I nuts to thinking I can do this myself and what size pex pipe should I run from the manifold system?

I am a do it yourself kind of guy, who has a few questions.
We have an old house with a hot water heat system. It is two zones system with a 2" feed and return for both floors. Off the feed and return is a 3/4" pipe that runs to each cast iron radiator. We want to put a thermostat in each room and replace the network of pipes that we have in the basement with a manifold pex system. Am I nuts to thinking I can do this myself and what size pex pipe should I run from the manifold system?

Dear Sir you are going to open a giant can of worms by attempting this. I suggest you read up on PEX and its applications. You will still need the 2 inch main headers to carry enough heat to the smaller circuits so I do not see a gain here. You can put a 24 volt zone valve in each of the 3/4 lines you want to control and install a 24 volt transformer and thermostat for each line.It will be a lot cheaper and with much less headache.