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Connect copper to steel pipes
Thank you all for responding to my post. My house is cold so I need to move forward soon!
My plan is to use a Trinity 150 combi with an indirect tank for DHW. Then, for heat, six high temp zones, one for the basement (mostly above ground), one to include both the living room and dining room which contains the only thermostat, one for the kitchen, and one for each of three bedrooms. Each radiator, except for LR and DR will have a TRV. The system will have a Pressure Bypass Differential Valve. The six zone manifold will be run off one circulator pump.
I may instead decide to put the basement on its own circulator pump with it's own thermostat.
Since I'm installing TRV's anyway, I want to get rid of the iron pipe which will also solve some architectural issuse. I'll reach each radiator with 3/4" Pex-AL-Pex unless I can be convinced to run 1/2".
I'm unsure if I should put balancing valves on the manifold or not. The zones will be unequal.
I'll be replacing a 100K BTU standard boiler. The water temp must have been (boiler is totally dead now) high, probably 180 or so. someone suggested 130 degree water would do fine. Although this would allow for higher modulation I'm not sure if I can get adequate BTUs at that temp.
I'd really appreciate comments with respect to the manifolds, tube size and boiler manufacturer.