Chimney Height for a Target Draft
The inverse of the chimney-draft tile: the stack height needed to produce a target NET 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.
Formula and source
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.
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