I have hot water heat with cast iron radiators. Right now the piping
is 3/4 in. copper in the immediate vicinity of the boiler (which is
about 15 years old) but it then connects to old steel pipes. The steel
pipes are sizable (the mains are maybe 2.5 in. and the loops to each
radiator are 1.5 in.). I think the system used to be gravity-driven
judging by the size of the pipes and the way the mains slope slightly
up away from the boiler. But now there is a pump. I have been
thinking I might want to replace the old steel piping, mainly to
increase headroom in the basement, but also to reroute some of the
lines which go through outside walls. Could I replace the steel with
copper, and if so, how to size the lines? Is there any kind of plastic
piping that is suitable for this application? Are there particular
advantages or disadvantages of doing this I should know about? Thanks,
-- H

here in buffalo ny the first floor has baseboard radiators, the second
and third floors have old fashioned radiators. the boiler is from 1990.

sounds just like our house next door. here's some of what i learned
since 1978:
1. first insulate the house [oops we didn't include the basement]. all
radiators must be inside insulated walls and heated in winter or they
will freeze and break like one of mine in a back stairwell when we
turned off its supply line in the basement to save money. you will now
have to shovel snow around the house since you are not warming up the
walkways with your warm basement like i am. but there are less icicles
forming on the gutters from wasted heat rising into the attic.
2. your basement may have comfortable but waste heat from all those
properly sized pipes for your radiators without modern insulation on
them. if you do what you suggest it will get cold down there and you
won't need any headroom because you will be living upstairs in the
comfortable insulated and heated habitable area of the house.
3. if you are going to reduce the amount of water in your system it
will affect the way your system operates. your local hvac guy will be
trying to figure this out to adjust the boiler for this and considering
your tankless boiler.
4. if you are thinking of replacing cast iron radiatiors stop now. it
takes wall to wall baseboards full of modern radiator piping to replace
a big hot old radiator.
5. add as many zone valves and zones and thermostats as you can afford
if you update your system. we changed from 2 to 4.
6. hang a copy of your boiler manual and the manual for every component
of your system that you searched for at www.google.com and printed out
by the boiler but above flood level. also list your annual maintenance
steps that you perform regarding the expansion tank and so forth at the
end of each summer.

i found basement insulation info in great detail at:
http://www.buildingscience.com/resources/basements.htm

You dont want pipes in outside walls they will freeze.

"buffalobill" wrote in message


4. if you are thinking of replacing cast iron radiatiors stop now. it
takes wall to wall baseboards full of modern radiator piping to replace
a big hot old radiator.

Mixing tube and fin baseboard and ci radiators is a problem with balance
too. If you do replace, use ci baseboard of the same capacity.

Couple things in response/clarification:

-- Yes I want to keep the radiators, like them a lot.
-- I am not too concerned about basement waste heat, currently have a
teenager living down there. (If he's good, someday we might let him
come upstairs.)
-- currently some of the (steel) pipes to the upstairs radiators go
through outside walls. While that has not caused problems in the 10
years we have occupied the house, it certainly is not real
energy-efficient; one purpose of redoing the pipes would be to get away
from that.
-- mainly I am curious if anyone has done this sort of thing and has
any tips. Also, curious if it would be practical to use CPVC or other
plastic pipe rather than copper.

-- H

"Heathcliff" wrote in message
currently have a
teenager living down there. (If he's good, someday we might let him
come upstairs.)


Heh, heh, he'll be there for life.


-- currently some of the (steel) pipes to the upstairs radiators go
through outside walls. While that has not caused problems in the 10
years we have occupied the house, it certainly is not real
energy-efficient; one purpose of redoing the pipes would be to get away
from that.

I'm not sure that he gains would offset much of the cost of a re-do of them.
If the wall cavity is insulated, there shold be little loss around the pipe.

Also, curious if it would be practical to use CPVC or other
plastic pipe rather than copper.

If anything, PEX would be my first choice. While it is capable of taking
180 degrees, it is designed for 140.

You dont use plastic for a boiler, think copper or galvanised.