PEX for older system?

Brian Tober

Thanks for the reply. Let me clarify what I was thinking of doing. It is a hot water system with 3 zones that have iron pipes for the main loop with 2 pipes off the main with diverter Tees to each Rad. Can I run new mains using Rigid PEX pipe or the PEX AL pipe in the crawlspace basically just duplicating what exisits using plastic pipe? If I could use flexible rolled PEX in the crawl as the Main loop that would be awesome so I wouldnt have to solder elbows at every twist and turn. What size main would you use? It has 1/2" branches now to each Rad. now. Would 1" be good with 1/2" branches?

Brian Tober

PEX on older system

I am replacing a boiler with 3 smaller ones in our apt house so tenants will each have sep. gas bills. The house has cast iron radiators already in 3 sep. zone loops with sep. circulators so it should be pretty smooth conversion. The system uses diverter tees off the main loop to each rad. I want to replace all the old piping in the crawl space since its really old iron pipe with repair patches all over. My question is: Can I use PEX pipe for the main loops and branches to each rad? I guess they dont make Pex diverter tees for the branches tho so i have to use the standard kind. Can I run PEX right up to the boiler? This would be a huge time saver for this project but I never used pex before. Thanks for any advice!

Steamhead

I wouldn't use PEX on a diverter-tee system

but they do still make copper diverter tees- that's what I'd use. This type of system relies on proper pressure drops which are inter-related. Since PEX is flexible, the pressure drop in a given length could change, affecting water distribution.

Repiping the system as two-pipe with PEX might be an option here, but the rads at the end of the diverter-tee loop might then be a bit oversized since in the diverter-tee system they were fed with slightly cooler water. You could cure this with TRVs if they're not in the room with the thermostat.

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Ross_7

Home Run system

You could gut the piping, and do a home run system to each corresponding boiler with pex manifold. This would also reduce the temperature drop that you would have with a monoflo system.

wetheat1_2

Pressure Drop

I would seriously doubt that the expansion or contraction of PEX tubing would have a significant if even measurable effect on the pressure drop in a system or circuit. A home run application bringing each rad back to a manifold would give the ability to tune the flow without the use of diverter tee's.

Tim D.