pex to cast rads

kevin coppinger_4

panel rads from 2 manifolds....no reason why not. Just size the lines properly....kpc

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aji

(Warning:DIYer :-)
I have a very large room with 4 large cast iron radiators.
I want to run Pex to each of the rads. The floor will be hardwood on a 6 inch subfloor. The subfloor sits on a slab so there will be no access after finished.(slab->2x6s on edge->plywood->hardwood).
The Pex will run through the subfloor.

I can't run the pex all the way to the boiler so I'd like to put a manifold under the floor (The manifold would have an access panel) Then just run one supply and return from the boiler to the manfold.

Is it ok to use Pex for cast Iron rads? Pex-Al-Pex?
I don't need to balance the rads (same room) so could I use a homemade manifold?
How do you make a manifold so that each branch has even flow?
Would 3/4" Pex supply a 17,000 btu rad?

I'll stop there for now...
I know, I know, I should hire a pro, but I'd like to at least figure some things out since it isn't a standard install.
Thanks

Brad White_164

Nothing to it

I prefer Pex-Al-Pex for no other reason than it has three layers, behaves well and does not cost a lot more...

The only way to make the manifold runouts self-balancing is to make them have the same pressure drop (same length and number of fittings) and assuming that the radiators have equal pressure drops too. I would pipe the manifolds reverse-return, meaning essentially that your supply header inlet and return header outlet are pointed in opposite directions. This is to distract the flow from taking obvious shortcuts.

Don't sweat the flow rate too much, a little difference in flow means almost imperceptable output in the radiator.

I might suggest that you use copper or iron pipe near the radiator to below the floor and use PEX below the floor. The exposed metal pipe will be more durable than exposed Pex or PAP.

3/4" PEX will easily handle 17,000 BTU's (1.7 GPM at a 20-degree drop).

Might this also be an opportunity to add TRV's to the radiators?

A good source of copper manifolds is Alberta Tee; there are others. Earthlee is a good company but I am not fully familiar with their copper line, just their steel line which is excellent.