Hydronic Radiant Floor Loop Sizing

The loop count against the per-loop length limit so no loop exceeds the head the manifold can push, and the design flow per loop from the room load: tube = area x 12 / spacing, loops = ceil(tube / max loop), GPM = load / (500 x delta-T) (300 ft^2 at 6 in o.c., 9,000 Btu/hr -> 600 ft, 2 loops, 0.45 GPM per loop). The manufacturer's tubing tables and the room-by-room heat loss govern the final layout; this sizes footage, loops, and flow from a uniform load, not the panel surface-temperature design.

tube_ft = floor_area_ft2 x 12 / spacing_in; loops = ceil(tube_ft / max_loop_ft); per_loop_ft = tube_ft / loops; total_gpm = load_btuhr / (500 x design_dt); per_loop_gpm = total_gpm / loops.

First-principles tube-footage, loop-count, and the GPM = Q / (500 x delta-T) hydronic flow relation, by name; the radiant-panel practice per ASHRAE HVAC Systems and Equipment (radiant panel chapter) and the Radiant Panel Association. Not edition-bound.

The footage is area over the on-center spacing, the loop count is the footage over the loop limit, and the 500 x delta-T flow constant is the standard water-side relation; all public.

Estimate. AHJ and licensed professional govern.

Field names used by the API: floor_area_ft2, spacing_in, load_btuhr, max_loop_ft, design_dt, tube_ft, loops, total_gpm, per_loop_gpm

• Footage one foot of tube per (spacing / 12) ft^2 of floor, a uniform serpentine layoutradiant-panel practice
• Loop limit max loop length default 300 ft for 1/2 in PEX; the manufacturer's table governs the actual limit by tube sizeASHRAE HVAC Systems and Equipment
• Flow constant GPM = Btu/hr / (500 x delta-T), the standard water-side sensible-heat relationASHRAE Fundamentals