Radiator Repipe with pex

Mbyrnes92

Looking to repipe my house with pex al pex with my original radiators. Should I pipe it in a 2 pipe reverse return? I drew out a diagram on what I think I should do as far as a reverse return, if anyone can give me some tips I would appreciate it greatly. 

Ironman

Diagram?

More info about the type of system, radiators, size of boiler, present piping, etc.

Mbyrnes92

Forced hot water, Had steel piping with iron fittings, not too sure of size of boiler...the rads are about 4’ Long  3’ tall 1.5’ wide

Jamie Hall

That should be OK -- provided you can do two things: first, keep the temperature of you water below the recommended maximum for PEX of 180 F. (The actual rated maximum temperature for PEX is 200 F, but it shouldn't be used above 180). Second, PEX expands and sags like crazy when it's heated, so be sure to give it full support -- either very closely spaced hangers or, better, in a trough, and with plenty of provision for expansion.

Ironman

Jamie,
He's proposing the use of pex-al-pex which has about the same expansion rate as copper due to the aluminum core.

Hangers about every six feet should be adequate.

The problem is that we need to know the btu output of the boiler (it's on the tag) and the EDR of the rad's to know what SIZE pex-al-pex is required.

Special pressing tools are also required as well as special fittings.

Here’s an EDR table:

Mbyrnes92

155000 btu/hour 

Mbyrnes92

And also I want to add In trvs and is it necessary to use diverted tees or just reg tees?

Jamie Hall

Regular Ts. Diverter Ts are for monoflow systems. If you're going to throw in TRVs, it would be best if the pump were set up for delta P operation.

Mbyrnes92

Thank you. Any suggestion on pipe size? And the 2 pipe system of definitely the way to go over a regular 1 pipe system 

hot_rod

Also, once you know what radiators you have see how they match the room by room heat load. In some cases you can run lower supply temperatures for much, maybe most of the year.

This journal has some ideas and formulas for that.
https://www.caleffi.com/sites/default/files/file/idronics_25_na.pdf

Viessmann talks about the 3:1 rule. For every 3° you lower the SWT, 1% lower fuel consumption.

Mbyrnes92

Tthis is my boiler set up, going to relocate it and use a manifold with 2 zones 1 for upstairs and 1 for downstairs. Pump is on supply, can I run this set up with the same pump and just reconnect all lines? 

Mbyrnes92