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Snow Melt system setup pex sizing


I am in the works on a new construction home i am gonna move into the next few months.  I have some knowlege on repair and installation of hydronic systems from working with my father, but I do have a few questions on my snowmelt design.  I am not a mechanical engineer by any means ( I am a physics degee holder), so I do want to make sure all my numbers look good before I go purchase items.

I have a Peerless 95% efficency boiler. 199,000 BTU (I got this for free from my dad. its used but 3 months old)

I have 5 areas that I would want heated for snowmelt. Driveway, Garage Walkway, Front Walkway/steps, front porch, and back porch.

I am using 120 BTU/sq ft. Delta T falls between 20 and 30 degrees F

My main question is what pex size should I use on the  driveways and porches

Heres my setup

Driveway 5 loops, 280 feet loop of 5/8" or 3/4" PEX

Porches are a total of 2 loops, 280 feet each loop. 5/8" or 3/4" Pex. Walkways: 2 loops 160 feet each loop. 1/2" Pex for sure.

I setup an excel sheet to calculate pipe resistance, head loss, flow and compared that to pump diagrams.

I think a B&G PL30 1/12 HP pump fits the bill no matter what size PEX I use (that and my father has a spare he is not going to use still in the box)

If I go with 5/8" pex on driveway and porches, I get 15.5GPM with a HL of 13 ft.

If I use 3/4" PEX, I get 18.7GPM with HL of 10.4ft.

I have taken into consideration the fact that a glycol mix will affect resistance and head loss.

 What size pex for the 280 foot PEX runs, 5/8" or 3/4" 

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