Door Closer Size, Opening Force, and Where the Overage Is

A closer sized down until the opening force meets the limit may not have the power to close the door against its latch, its gasketing, and the building's stack pressure -- and a fire door that does not latch is a failed fire door. When both cannot be met the answer is a lower-friction hinge set, a different latch, addressing the pressure difference across the door, or a power operator, not a weaker spring. THE READING IS OFTEN NOT THE CLOSER. A 36 by 84 in door in a room held 0.03 in wc above the corridor is 21 sq ft carrying 3.3 lbf of pressure force, and because the door is hinged at one edge and pulled at the other, about 1.6 lbf of that lands on the person's hand. A 6.5 lbf reading against a 5 lbf limit is a 4.9 lbf closer and 1.6 lbf of building: turning the spring down fixes the gauge and breaks the latching, and the actual fix is mechanical. The split is printed so the argument is on paper before anyone reaches for a screwdriver. The adjustments are commonly confused too. Spring power sets the opening force; sweep speed and latch speed set how fast it closes and are hydraulic rather than spring; backcheck protects the door and the closer from being thrown open into a wall. Slowing the sweep does not reduce opening force. And accessibility imposes a minimum closing TIME as well as a maximum force, so a door tuned to slam shut fails even when its force reading is fine. A sizing band and a limit comparison. It does not select a closer, which is a manufacturer choice based on width, weight, mounting, and the pressure condition. Limits and how they are measured differ between the accessibility standards, the building code, and the life safety code, and fire doors are treated differently again. It does not evaluate hinge condition, latch and strike alignment, or gasketing drag, all of which change the measured force and are usually the real problem, and it does not address delayed egress, electrified hardware, or power operators. On a rated door the assembly must close and latch from any position, and adjusting below the power needed to do that defeats a life-safety device whatever the gauge says. NFPA 80, the adopted building and accessibility codes, the manufacturers' listings, and the AHJ govern.

closer size band = one size per six inches of door width from a 30 in size 1, stepped up for a heavy leaf or a pressure difference; the force a pressure difference adds at the pull = door area x pressure x 5.2 lbf per sq ft per in wc / 2; closer force = measured force - that.

ANSI/BHMA A156.4 closer size bands by door width, by name, with the accessibility and building-code opening force limits and the minimum closing time named, and NFPA 80 cited for rated doors. Limits are entered from the adopted code; the closer itself is a manufacturer selection from its own chart.

A size band from door width and a subtraction on the user's own gauge reading; no manufacturer sizing chart or code table is reproduced.

Estimate. AHJ and licensed professional govern.

Field names used by the API: door_width_in, door_height_in, door_weight_lb, measured_opening_force_lbf, force_limit_lbf, measured_closing_time_s, min_closing_time_s, pressure_difference_inwc, closer_size, door_area_sqft, pressure_force_lbf, closer_force_lbf, force_margin_lbf

• The two requirements fight a closer weak enough to meet the force limit may not latch the door, and a fire door that does not latch has failedNFPA 80
• Half the pressure force lands at the hand a door is a lever hinged at one edge, so a small pressure difference reads as a hardware problemstatics
• Spring power is not sweep speed slowing the sweep does not reduce opening force, and the two adjustments are independentcloser manufacturer data