Can someone help me. I am renovating a turn of the century house, 8000 sq', changed into 5 apartments sometime in the 40's. The house has been gutted and all systems replaced (electrical, plumbing, waste water,etc.)
The house is heated with the original cast iron radiators and they work wonderfully. The same boiler is being used as before and the same radiators. One change is that the house will be insulated (it wasn't before). The other change is that each apartment will be on it's own zone whereas before the whole house was one big zone.
The original steel pipe that supplied the radiators with hot water (not steam) have been removed and we will replace them with pex al pex (manufacturer's name: kitec). There are approxiately 5-6 radiators per apartment. They are large units 6-7 sections each on average and for rough calculations I will assign a heat output of approx. 4000 btu per rad.
The manifold that supplys them is 1 1/4 " Cu with 3/4" zone feeds. My plumbing supplier calculated that 3/4" pex will satisfy the heating requirements of the 5-6 radiators, that is one zone with 3/4" supply in parallel to 5-6 rads.
This seems a little small to me, the original pipes were massive, I realize this was originally a system without a circulating pump. We have temporarily hooked up a few of the rads for heat over the winter using 1/2" and 3/4" pex with each rad having it's own supply and there is very obviously an abundant supply of heat in this temporary configuration. I will hook up 1 apt. as a test. There is another consideration, if the test works satisfactorily, will the 1 1/4" manifold supply all 5 zones (apartments) when they call for heat at the same time? (the manifold is new, before it was a jumble of pipes feeding one another).
Before I purchase 10 miles of 3/4' and install it I'd better be sure I have the right size. The test apartment is a good idea, but can anybody give me a correctly calculated size? Again, I have discounted the boiler, circulating pump, and radiators for supplying heat the question is the pipe sizing and manifold sizing.