Thanks for the good reading- learned a lot here.
Problem: slow and uneven heating from my hot water baseboards. 1st floor is warm and cozy, and the 2nd floor is usually cold. Some of the bedrooms are fine, other bedrooms piped further away are cold. Baseboards are properly sized as per heating company I called for help.
My system uses an 8-14 year old NG boiler, connected by 2 1/4 copper into some 3" gravity cast iron pipes The circulator pump on the return side of the boiler only runs while the boiler is firing, not before or after. My observation is that for about the first 20 minutes the boiler is running, none of the baseboards are very warm except the shortest runs from the boiler, and most of the heat goes to heating up those giant cast iron pipes. My intuition is that you'd want the circulator to run well after the boiler has stopped firing to keep moving heat through the baseboards, but the aquastat only has a 2-wire on-off to the thermostat.
Wanted to repipe the basement with aluminum barrier PEX onto the 1" copper pipes which run to the rads. Should speed up rad time-to-temp. Also wanted to install zone valves and a new aquastat w/ zone controller, maybe doing primary-secondary piping.
Had a couple estimates- came in high (over 7500). 1st guy didn't want to remove cast iron piping because they heat the basement. I mentioned primary-secondary piping and zoning and he said my boiler can't handle primary-secondary since it's a big cast iron combi. 2nd guy suggested installing thermostatic valves on each rad and/or adding minisplits to each room which can help the baseboards heat.
My questions are:
1.) Is repiping basement with O2-barrier PEX a terrible idea? Want to save some headroom too. What size is good? 1"?
2.) If i want to zone my system, what's the best way? Primary-secondary, or just a zone-control panel and and zone valves and my blow torch?
3.) alternatives like thermostatic valve on each rad or minisplits - opinions?
Photos of my basement piping:http://s84.photobucket.com/user/tazman1937/library/Heating system