Chimney Height for a Target Draft

H = D_net_target / (net_factor x 0.52 x B x (1/T_o - 1/T_m)) with temperatures absolute (Rankine). A 400 F mean flue temp over 60 F ambient at sea level needs about 30 ft for a 0.10 in wc net draft; at altitude the thinner air demands a taller stack. Enter the net draft the appliance needs (the 0.5-0.8 factor already accounts for flow and fitting losses). A design aid, not a venting sign-off.

T_o_R = ambient_temp_f + 460; T_m_R = mean_flue_temp_f + 460; H = target_draft_net_inwc / (net_factor x 0.52 x baro_psia x (1/T_o_R - 1/T_m_R)) [ft]; the inverse of D_net = net_factor x 0.52 x B x H x (1/T_o - 1/T_m).

ASHRAE Handbook HVAC Systems (chimney/vent) / NFPA 211 theoretical chimney draft solved for the stack height, 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: target_draft_net_inwc, ambient_temp_f, mean_flue_temp_f, baro_psia, net_factor, required_height_ft

• Net-draft target the target is the net available draft; the net_factor (0.5 to 0.8) already removes flow and fitting losses from the theoretical no-flow draftASHRAE 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