Have the old hot water/boiler system to heat my 1955 house. Water circulation by electric pump. Oil/electric to heat the water. I want to change part of the supply pipe to the radiators that is visible in a room in the basement.

Is PEX tubing good for hot water furnace applications ? The main supply now to the heaters upstairs is 1 1/4 OD cast iron pipe. I want to change/merge cast iron to PEX.

Also, do the old cast iron "T's that connect to the pipes leading to the heaters upstairs have any sort of water deflectors inside to send the water into the heater upstairs ? Will a PEX "T" work as well to send the water up into the radiator ? Need advice !!!

To answer your last question first. If they are "Mono-flo" tees they DO have "deflectors" and if you eliminate them the system will NOT work properly.

If they are tee'd off a main, there is something in them to divert the water.

Here's a cutaway drawing of one style showing the deflector/diverter "bump" inside:





Edited 2 times.

usually there are two tees to each radiator. one is a monoflo or scoop tee while the other is a regular tee.
you can use a pex tee for the standard tee but not for the scoop tee.
but, you do have to be careful to not reduce the size of the main pipe by putting in a smaller pex tee.

Interesting note, I have the same setup (although I replaced oil with gas), but there are 2 heating loops that run around the basement, one supply and the other return. Each cast iron radiator is plumbed to the supply side and the return side. Same setup with 1-1/4" iron pipe with the diverter tees on the supply side.

The radiator in the kitchen was moved at some point, and the original pipes going to it were cut, although they left the original tees in the supply/return loops. The pipes going to the radiator were reduced with fittings to 1/2" copper, which seems like it would starve that radiator, but that one gives off more heat than any other radiator in the house!!

Two pipe systems do not NEED diversion tees, because the flow to the radiators can be accomplished with changes in pipe size. In face, a diversion tee could be detrimental, because the diverted flow does NOT return to the same main the way it does with a one pipe system.

any old cast iron monoflo tees i have seen were true monoflo. they had that funnel shaped diverter inside rather than an angle piece that acts like a scoop.

Thanks for the info on mono flo T's from PEX. That is what I was looking for. Will look for them before starting my project. Are these T's easy to find in store or only at dedicated plumbing shops ?



Edited 1 times.

I would be running a one inch PEX tubing for the supply line. So far have not found a one inch diameter monoflo T on the net. Seems 3/4 is the max size. Do not want to reduce the flow at the T's. Are there one inch monoflo T's available ?

lots of them out there.. [#$%&.com]
they also come in cast iron threaded so you don't have to solder. just screw in adapters. but these are harder to find..