Piping size for myson panels

rosy

A mechanical room and control panel are about 12' below grade and three Myson panel radiators (2) 24" x 18" and (1) 32" x 24" ( in three bathrooms, each fed by approximately 20 feet of 1/2 - 02 pex. Supply and return lines for the three radiators will run to a crawlspace and route into a 1" copper manifold with 1/2" balancing valves. The Myson's will have TRV valves.

Myson rates the 24 x 18's at around 3k btus and the 32 x 24 at 4.5k btus.
The question is whether to supply those manifolds with 3/4" supply and return pipes or 1/2"? Pump will be a Grundfos 15/58 3 spd. Seems like 3/4" is the way to go to get enough head to overcome the situation of all 3 activating at the same time. The rise from the manifolds in the crawlspace is 2-3 feet.

Thanks,

Dave

Ironman

So, are you saying the total for all three of the 24 x18's is 3k btus or 3k btus for each totaling 9k btus?

psb75

No. Two at 3 btuh ea. and one at 4.5 btuh for a total of 10.5 btuh.

Ironman

The height makes no difference in a closed loop.

You'd need a minimum of 1" copper to feed the manifolds using a standard 20* delta T.

Rich_49

1/2 is fine .

psb75

Sorry, I meant 10.5K btuh.

TAG

FYI -- I have used the Buderus panels w/ bypass on three houses using 1/2 pex. Two houses have third floor ... w/o issue. I think at the time I was told keep it around 12k max BTU per zone w/ 1/2 inch.

These are old school CI Buderus boilers -- panels are the main loop using outdoor reset .. small brute primary pump. All the panels have the Danfoss thermostats.

It's really a great system if you can lay out the panels properly