Raising radiator plumbing in basement

Continental

Hi!

I'm in the planning stages of a basement remodel and have a typical problem with hanging iron radiator plumbing- boxing it will eat way too much headroom. I'd like to redo the system using PEX and at least two pumps to create zones while I'm at it. The material costs aren't bad (or at least are in budget)- I've found a custom manifold company that will do the complicated work with the 'folds and pumps and then ship to me. What has me stymied and confused is linking the PEX to the old radiator- Can I cut the old pipe in the basement joist space and have a welder (carefully) attach a PEX-compatible fitting? Is there some sort of compression fitting that I can use? Am I better off running PEX all the way to the rads (upstairs runs would be interesting...)? If so I suppose that there is a Iron to PEX fitting that will screw into the the radiators.

This doesn't sound like a huge deal (I'm comfortable with planning and running boiler to radiator) but when I had it quoted I was blown away with the prices (although everything home-repair related is hideous around here)

Any help or advice on all the bits that I'm missing is hugely appreciated.

Cheers,

KW in Arlington VA

Leah Frances

I would post this question at www.heatinghelp.com they are super helpful and knowledgeable.

__________________
If I could only remember to THINK about what I was doing before I did it.

Bondo

Ayuh,... You'll have to pick,+ choose where to make the transitions..
You can't weld something up, you need to transition at some joint somewhere...
Cutting,+ rethreading would be a nightmare...

Continental

So, I have two choices- at the radiator or at the elbow, possibly a mix of both (upstairs rads might be a bear). I assume that there are pretty standard PEX fittings that reduce 2" iron to an appropriate PEX diameter? Then run the PEX to a in/out trunk and back to the boiler.

The flow diagram that I have in my head is something like:

Main --> valve --> Boiler --> manifold a/b zone --> Circulation pump (a) --> Hot PEX Trunk --> Hot PEX Stem --> Hot Radiator --> Cold Rad --> Return stem --> return trunk --> expansion tank --> check valve --> boiler.

Am I missing any pieces? Drain valve at least and I'm not sure how the main to boiler water lever is monitored/controlled.

How do you calculate heat loss by volume/distance in a trunk and stem given material and insulation (PEX with low dense foam)?

Do I need an expansion tank for each zone or can both zones come into the same tank?

Thanks!