Theoretical Chimney Draft

D_t = 0.52 x B x H x (1/T_o - 1/T_m) with temperatures absolute (Rankine), in inches of water column, plus a net-available estimate (factor 0.5-0.8). This is the no-flow draft; the barometric pressure must be altitude-corrected (thinner air cuts the draft) and T_m is the mean flue temp. A design aid, not a venting sign-off.

T_o_R = ambient_temp_f + 460; T_m_R = mean_flue_temp_f + 460; D_t = 0.52 x baro_psia x stack_height_ft x (1/T_o_R - 1/T_m_R) [in wc]; D_net = net_factor x D_t.

ASHRAE Handbook HVAC Systems (chimney/vent) / NFPA 211 theoretical chimney draft, by name.

The theoretical-draft relation is standard chimney/vent design practice; the venting standard and appliance instructions govern the actual sign-off.

Estimate. AHJ and licensed professional govern.

Field names used by the API: stack_height_ft, ambient_temp_f, mean_flue_temp_f, baro_psia, net_factor, draft_theoretical_inwc, draft_net_inwc

• No-flow theoretical D_t is the no-flow draft; net available after flow/fitting losses is about 0.5 to 0.8 of itASHRAE Handbook HVAC Systems
• Altitude and absolute temps barometric pressure must be altitude-corrected; temperatures are absolute (Rankine), T_m the mean flue tempASHRAE / NFPA 211