UL 10B vs UL 10C: What's the Difference for Fire Doors?

When specifying a UL fire-rated door, you may see two similar standards: UL 10B and UL 10C.

Both are fire test standards for door assemblies, but they use different pressure conditions during testing. This difference matters because the required standard can depend on the type of door, applicable building code, and project specifications.

This guide explains the difference between UL 10B and UL 10C and what buyers should check before ordering fire-rated doors.

What Is UL 10B?

UL 10B, Fire Tests of Door Assemblies, is commonly referred to as a neutral-pressure fire test.

During the test, the neutral pressure plane is established at the top of the door assembly. Most of the door is therefore exposed to negative furnace pressure.

Under these conditions, air tends to be drawn from the unexposed side toward the furnace through gaps around the door, frame, glazing, and other openings.

UL 10B is still used for certain types of fire door assemblies and applications.

What Is UL 10C?

UL 10C, Positive Pressure Fire Tests of Door Assemblies, evaluates fire door assemblies under positive-pressure conditions.

In a UL 10C test, the neutral pressure plane is established approximately 40 inches (1,016 mm) above the bottom of the test specimen. Areas above this level are exposed to positive furnace pressure.

As a result, hot furnace gases are pushed toward and through gaps around the door assembly and hardware preparations. This creates different exposure conditions from the UL 10B test.

For many common side-hinged and pivoted swinging fire doors used in projects governed by the International Building Code (IBC), positive-pressure testing is required.

UL 10B vs UL 10C: Key Differences

Item	UL 10B	UL 10C
Test type	Neutral pressure	Positive pressure
Neutral pressure plane	At the top of the assembly	Approx. 40 in. (1,016 mm) above the bottom
Pressure over most of door	Negative	Positive above the neutral pressure plane
Gas movement around gaps	Air tends to be drawn toward the furnace	Hot furnace gases can be forced through gaps
Typical application	Certain fire door types and applications	Commonly required for side-hinged or pivoted swinging fire doors under IBC requirements

The important point is that UL 10B and UL 10C are not simply two different fire-rating durations.

A 90-minute fire door, for example, describes the duration of its fire-protection rating. UL 10B or UL 10C describes the test method and pressure conditions used to evaluate the assembly.

Is UL 10C Better Than UL 10B?

Not necessarily.

UL 10C creates positive-pressure conditions over much of the door assembly and can expose gaps and hardware preparations to hot furnace gases differently from UL 10B.

However, that does not mean buyers should automatically specify UL 10C for every fire door.

The correct standard depends on the door type, applicable building code, project specifications, and requirements of the Authority Having Jurisdiction (AHJ).

For example, current IBC provisions require side-hinged and pivoted swinging fire door assemblies to be tested to UL 10C or NFPA 252 using the positive-pressure method.

Other types of fire door assemblies may be permitted to use UL 10B or NFPA 252 under different pressure conditions.

Does UL 10C Replace UL 10B?

No.

A common misunderstanding is that UL 10C is simply a newer standard that replaced UL 10B.

Both standards remain relevant. The appropriate test standard depends on the fire door application and the code or specification governing the project.

For buyers, the practical question is therefore not:

"Which standard is newer?"

but:

"Which standard does my project require?"

What Should Buyers Check Before Ordering?

Before purchasing UL fire-rated doors, confirm the following with your project team, architect, consultant, or local AHJ:

Required fire rating, such as 20, 45, 60, 90, or 180 minutes

Required test standard, such as UL 10B or UL 10C

Door type and opening configuration

Requirements for the door, frame, glazing, and hardware

Any smoke and draft control requirements

Applicable local building and fire codes

Do not select a fire door based only on the fire-rating duration. The complete opening needs to meet the requirements specified for the project.

UL 10B and UL 10C Fire Doors from XZIC

Shanghai Xunzhong Industry Co., Ltd. (XZIC) manufactures UL-listed steel and wood fire door products, with certifications covering both UL 10B and UL 10C.

When selecting fire doors for a project, the required certification should be confirmed against the project specifications and applicable code requirements rather than assuming one standard applies to every opening.

If you are unsure whether your project requires UL 10B or UL 10C, send us your door schedule, specifications, or fire door requirements. Our team can review the information and help you identify a suitable fire door solution for your project.