Hydronic Snowmelt Load and Boiler Sizing (ASHRAE)
The heated-driveway sizing balance: warm the falling snow to the 33 F film, melt it (746 Btu/hr-ft^2 per in/hr of water equivalent), and over the snow-free fraction pay the wet surface's wind-driven convective and evaporative losses - q_o = q_s + q_m + A_r(q_h + q_e), the ASHRAE / Chapman steady-state flux. The class is the design decision: the same 20 F, 10 mph storm runs 78 Btu/hr-ft^2 on a residential drive allowed to whiten (A_r = 0), 111 on a commercial walk (0.5), 144 on a must-stay-black hospital ramp (1.0). Boiler = flux x area plus ~20% back loss. A sizing aid for the chosen storm, not an annual energy or a stamped design.
Formula and source
q_o = q_s + q_m + A_r(q_h + q_e), with q_s = 2.6 s (33 - t_a); q_m = 746 s; q_h = 11.4 (0.0201 V + 0.055)(33 - t_a); q_e = 1075.5 (0.0201 V + 0.055)(0.188 - p_av); p_av from the Magnus curve x RH; boiler = q_o x area x (1 + back_loss); t_m ~ 0.5 q_o + 33.
ASHRAE Handbook (HVAC Applications, Snow Melting and Freeze Protection) steady-state surface flux, with the Chapman (1956) IP component forms as printed in Lund, Pavement Snow Melting (Geo-Heat Center / OSTI), by name.
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