Our house, built in 1950, has a one-pipe diverter tee system with
radiators (not cast iron, aluminum fin on copper, but they're not
baseboard) for our first floor heat (they used copper for the second
floor, but did it more like a two-pipe system). For some reason, it was
plumbed with a combination of cast iron and steel pipe rather than
copper. The steel pipes are now starting to rust and leak, and I need
to redo the system.

I'm going to use the same pipe sizes - 1" for the main loop and 1/2"
for the radiators. The existing system is hung from pipe hanger
material (that perforated flexible steel that comes in a roll) about 4"
from the bottom of the basement joists. I'd like to set up the new pipe
so it's against the joists, in fact, I'd like to notch the joists
slightly so I don't even need all of the 1 1/8 inch of clearance, since
I am refinishing the basement at the same time.

My concern is that I assume that the reason it was originally plumbed
hanging down instead of against the wood was to allow for
expansion/contraction and to prevent creaking. So how much leeway do I
have? Can I notch the joists and then use loosely connected pipe
hangers to snug it up close so I can still install my ceiling without
having to lose the additional space?

Also, any other suggestions regarding this system are appreciated. Even
though this is not the first house I've owned with this type of system,
it's the first time I've needed to do any major work on one.

Please respond in the newsgroups, please, this email address is a spam
target.

Thanks,

Steve