FHW supply line

[recruiter]

I have a 110 year old multi family house that has asbestos covered FHW supply and return lines feeding radiators on the first floor. (BTW: the asbestos is already encapsulated). The previous owner uncovered the 1 1/4" pipe, to a fitting, then connected copper reducers down to 3/4" in order to install a Slantfin 4 ft. baseboard radiator in the bathroom. Due to major renovations that are needed in the bathroom, I will be replacing the baseboard heater, since it was damaged during the renovations and the copper connections now leak at fittings.

I am looking to replace the copper with Pex.

1. Is the original 1 1/4" piping black pipe? 2. If so, will I be able to use a black pipe 1 1/4" to 3/4" reducer directly to a Pex brass connector without an issue of corrosion or electrolysis? 3. What would I use on the threads? Is tape OK?

Thanks
Dave

 

[frodo]

what type of system ? loop, closed loop, 2 pipe, single, reverse return ?

if you choke a 1 1/4 system to 3/4 your heating will suffer

 

[recruiter]

From what I see, I have a two-pipe direct return system.
I live in RI, USA.
We purchased this house in 1999, complete with all the former owner's mess-ups, which we have been trying to fix, one project at a time.
This baseboard unit is the last unit on the loop. I am not able to tell if there was originally a cast iron radiator like the rest of the apartment, replaced by this baseboard heater, or if he simply decided to tap into the line and add a new baseboard unit to it. More than likely, it was the first situation. Now I'm stuck trying to figure out how to work around it.

 

[frodo]

your heating lines are sized to deliver X gpm at your baseboard/infloor heat/fan units.

if you choke the system down by cutting out a section of 1 1/4 and replacing with 3/4 pex

which is actually 1/2'' ID you are seriously f--up.

you said the other owner did it. that is most likely your problem now.

the unit that is being served is not getting enough hot water flow {gpm} to be efficient



any time you transition from steel pipe to copper/brass you must use a dielectric union or nipple

it will rust out at that transition, if not

 

[recruiter]

I checked this out, again. It is actually an old gravity feed system. The boiler was replaced several years ago, and it now has circulator pumps installed.

I actually found the 2 original fittings that were removed to install the baseboard heater. Curiously, it is a 1 1/4" Tee (capped at the end) with a 3/4" leg. When I checked out all the other radiators in the apartment, they are all running on 3/4" pipe.

At first I thought there may be a 1 1/4" loop somewhere, but it's not the case. There are 2, 1 1/4" feed and return lines with 3/4" branches to each radiator.
Is this normal? What is the difference between the setup with the radiators vs. the 3/4" copper tubing for the baseboard that the previous owner installed?
Thanks