Ceiling Fan & Luminaire Box Support Calculator

The paddle-fan rule: 314.27(C)

A paddle fan spins and wobbles, so the box that holds it takes far more than a static load. 314.27(C) answers it with three numbers. A box used as the sole support of a fan must be listed and marked by its manufacturer as suitable for the purpose, so an ordinary lighting box is out from the start. A fan box with no weight marking is good for 35 lb, because the Code only requires a maximum-weight marking once a box is designed to carry more than 35 lb. Where a box is marked, it supports up to the marked figure, and no outlet box may support a fan over 70 lb. A heavier fan has to be supported independently of the box, from the building structure or a listed fan brace.

Fan vs luminaire: the limits side by side

The luminaire rule: 314.27(A)

A listed luminaire outlet box supports a luminaire weighing up to 50 lb, on a wall or a ceiling. Above 50 lb the luminaire must be supported independently of the outlet box, unless the box is listed and marked for the greater weight, in which case the marking governs. There is no 70 lb ceiling here, so a heavy chandelier on a box listed and marked for its weight is fine. One narrow allowance in 314.27(A)(1): a wall luminaire or lampholder of 6 lb or less may ride on another box or a plaster ring secured with at least two No. 6 or larger screws, rather than a dedicated luminaire box.

Worked example: a 52-inch fan with a light kit

A 52-inch paddle fan with a light kit and downrod weighs 38 lb all in. Mounted on a listed fan box with no weight marking, it fails: an unmarked fan box is limited to 35 lb, and 38 is over it. Swap in a fan box marked for 50 lb and the same fan passes, because 38 lb is within the 50 lb marking. Push the assembly to 44 lb with a larger light kit and it still passes on the 50 lb box. A 90 lb commercial fan passes on no outlet box at all, because 314.27(C) caps every box at 70 lb; it needs a fan brace or structural support carrying the load independently.

Common mistakes

• Hanging a fan on a lighting box. A standard luminaire box is never the sole support for a paddle fan, even a light one; 314.27(C) requires a listed, marked fan box.
• Reading the 70 lb cap as the box rating. 70 lb is the ceiling for any box; an unmarked fan box is only good for 35 lb, and a marked box is good for its own marking.
• Forgetting the accessories. Light kits, downrods, and glass add up; weigh the whole assembly, not just the motor.
• Confusing support with fill. Meeting 314.27 for weight does not satisfy 314.16 box fill; the conductor and device count is a separate calculation.
• Assuming a heavy chandelier always needs a strap. A luminaire over 50 lb is fine on a box that is listed and marked for the weight.

Frequently asked questions

How much weight can a ceiling fan box hold?

Under NEC 2020 314.27(C), an outlet box used as the sole support of a ceiling-suspended (paddle) fan must be listed and marked by its manufacturer as suitable for the purpose. A fan box that carries no maximum-weight marking is limited to 35 lb. A fan box marked with a maximum weight supports up to that marked value, which can never exceed 70 lb. A fan heavier than 70 lb cannot be supported by any outlet box and must be supported independently of the box.

Can a regular outlet box support a ceiling fan?

No. 314.27(C) requires that a box used as the sole support of a paddle fan be listed and marked by its manufacturer as suitable for ceiling-fan support. An ordinary lighting outlet box is not rated to be the sole support of any paddle fan, regardless of how light the fan is. Use a listed fan-support box or a fan-rated brace.

Does a fan box have to be marked with a weight?

A fan box must carry a maximum-weight marking only when it is designed to support a fan heavier than 35 lb. That is why an unmarked listed fan box is treated as good for up to 35 lb: if it were rated higher, the marking would be required. Above 35 lb you need a box whose marking states a maximum at least equal to the fan weight, up to the 70 lb ceiling.

How much weight can a box support for a light fixture?

NEC 2020 314.27(A) lets a listed luminaire outlet box support a luminaire weighing up to 50 lb. A luminaire heavier than 50 lb must be supported independently of the outlet box unless the box is listed and marked for the greater weight. Unlike paddle fans, luminaire boxes have no 70 lb ceiling, so a box listed and marked for a heavier luminaire may support it.

Can a light fixture be mounted to a device box or plaster ring?

314.27(A)(1) permits a wall-mounted luminaire or lampholder weighing 6 lb or less to be supported on another box or a plaster ring that is secured to a box, provided the luminaire or its supporting yoke is secured with no fewer than two No. 6 or larger screws. Heavier luminaires follow the general 50 lb box-support rule.

Does this calculator use the 2020 or 2023 NEC?

It uses the NEC 2020 text of 314.27(C) and 314.27(A). The 35 lb, 50 lb, and 70 lb support thresholds are long-standing and unchanged across the 2017, 2020, and 2023 editions. Always verify against the edition your jurisdiction has adopted.

Related calculators

• Box Fill Calculator: the 314.16 conductor and device volume for the same box - a separate rule from support weight.
• Pull/Junction Box Size Calculator: minimum pull and junction box dimensions for 4 AWG and larger per 314.28.
• Wire Size Calculator: ampacity, voltage drop, and OCPD for the fan or luminaire branch circuit.
• Breaker Size Calculator: the branch-circuit overcurrent device for the same circuit per 210.20(A) and 240.6(A).