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Sizing pex piping supplying cast iron radiators.

Richie921's picture

Sizing pex piping supplying cast iron radiators. (post #191341)

Richie921 on Fri, 07/16/2010 - 22:19 (updated 07/17/10 - 07:54) 
in

I am running pex to supply cast iron radiators that I am using in my home in both the old and newly added section. It is going to be a hot water system with 2 runs of pex to each radiator (supply and return). I'm using  manifolds off the boiler and using zone valves to control each radiator. The house has a basement, 1st floor, second floor and third floor under the roofline.  How do I size the pex pipe I'm using as the supply and returns? Thanks.

Richie

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So each radiator gets it's (post #191341, reply #1 of 7)

by Marson in reply to Richie921 [original] on Sat, 07/17/2010 - 04:20

So each radiator gets it's own home run back to the manifold?  I did my own system like that using 1/2" pex and it works great.  Of course there is a ton of caveats, and it's really a question for a heating system designer.

 

You might want to try this question over at heating help's "the wall".

Thanks, I'll check them out (post #191341, reply #2 of 7)

by Richie921 in reply to Marson [original] on Sat, 07/17/2010 - 04:24

Thanks, I'll check them out over there. Yes, each radiator gets it's own supply and return off the manifold.

Richie

Size the piping (post #191341, reply #3 of 7)

by Tim in reply to Richie921 [original] on Mon, 07/19/2010 - 09:49

whether it is made of cross-linked polyethylene or steel, to accomodate the required water flow rate. For the most part, you would size the pex at the same size as you would hard pipe, but most PEX fittings have reduced diameter than the tubing. For this reason, many jurisductions allow aquapex to be used in domestic plumbing systems, but only if provide "one size larger" than code minimums. For short runs, same size is fine, for longer runs, upsize it  one size. 1/2" up to 1 gpm, 5/8" up to 2 gpm, 3/4" up to 3 gpm.

IF you do not know how much water you need to provide to each radiator to provide the heat required to meet the demand of the spaces served by the radiators, get help.

radiator (post #191341, reply #4 of 7)

by k1c in reply to Richie921 [original] on Sat, 07/24/2010 - 22:53

This site may be useful, although your situation may need on site inspection for analysis.  Heatinghelp.com, and with more details such as number of (fins?) in each radiator, height and type of radiator.  How far each is from the boiler.  Do some research to learn how you can identify your radiators,  Sorry but my research was long time ago and I forgot all details.  Google Dan Holohan or what kind of radiators do I have?  Hope it helps.

radiators (post #191341, reply #5 of 7)

by k1c in reply to Richie921 [original] on Sat, 07/24/2010 - 23:04

Another thought:  you may be able to clean the old pipes, if applicable. 

two answers (post #191341, reply #6 of 7)

by NRTRob in reply to Richie921 [original] on Wed, 07/28/2010 - 13:34

short answer, use 3/4".  there, isn't that easy?  no single radiator I'm aware of would need more than that, ever.  course, that's bigger, stiffer, and more expensive.

the real answer is, you need to know what your flow rate requirements are.  that's dependent on heat load and water temperatures, as well as the size of the radiator.  the right answer could vary from 3/8" to 3/4" tubing, per radiator.

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Thanks guys.  Sorry I haven't (post #191341, reply #7 of 7)

by Richie921 in reply to NRTRob [original] on Mon, 08/09/2010 - 09:21

Thanks guys.  Sorry I haven't been on in a while...very very busy.  As llong as 3/4 is fine for all, I'll use that. Thanks again.

Richie