How To Measure Size of Exit Device？

Introduction

Exit devices, also known as panic bars or crash bars, are critical life safety components on commercial building doors. Whether you're a facility manager, a door hardware installer, or a building owner, there will come a time when you need to measure one. Perhaps you need a direct replacement for a broken unit, or you're specifying hardware for a new door. Getting the measurements wrong can lead to costly delays, incorrect orders, and doors that are non-compliant with fire codes.

This guide will demystify the process. We’ll break down the essential measurements for the most common types of exit devices, ensuring you can measure with confidence and accuracy.

Why Accurate Measurement is Non-Negotiable

Before we grab the tape measure, it's crucial to understand why precision matters.

· Compliance with Codes: Fire marshals and building codes (like NFPA 101 and IBC) have strict requirements for egress doors. An incorrectly sized device can impede safe exit and fail inspection.

· Functionality and Security: A device that is too long or too short won't mount correctly. Misaligned latch bolts won't engage the strike plate properly, compromising both security and operation.

· Cost Savings: Measuring correctly the first time prevents the hassle and expense of return shipping and re-ordering hardware.

Tools You'll Need

· A sturdy steel tape measure (a fabric one can stretch and give inaccurate readings).

· A notepad and pen to record each dimension.

· A ladder for measuring top rod devices safely.

Step 1: Identify Your Type of Exit Device

The first step is to identify what kind of exit device you have. The measurement process differs significantly between types. The three main categories are:

1.Rim Device: Mounts on the surface (rim) of the door. The latch bolt shoots horizontally into a strike on the door frame.

2.Mortise Device: Installed inside a pocket (mortise) cut into the door itself. Only the touchpad and base are visible on the door's surface.

3.Surface Vertical Rod Device: Mounts on the surface of the door but uses vertical rods running up and/or down to actuate latches at the top and bottom of the door. These can be regular (rods on the interior face) or concealed (rods inside the door).

Once you've identified your type, proceed to the specific measuring instructions.

Step 2: How to Measure a Rim Exit Device

This is the most straightforward type to measure.

The Critical Dimension: Backset

1.Measure the Door Width: First, measure the total width of the door from edge to edge.

2.Find the Center: Divide the total door width by two. This is the centerline of the door.

3.Measure the Backset: The backset is the distance from the center of the crossbar (or the center of the latchbolt) to the edge of the door. This is the most important measurement. Standard backsets are 3-3/4", 4", 4-1/2", or 5-1/2". It is vital to get this exact.

4.Measure the Overall Length: Measure the total length of the device itself from end to end. This ensures the new device will fit the door's proportions correctly.

Pro Tip: Also note the latchbolt projection (how far the bolt sticks out) and the door thickness, as these can sometimes vary.

Step 3: How to Measure a Mortise Exit Device

Because the mechanism is hidden inside the door, measuring a mortise device requires a bit more detective work.

The Critical Dimension: Mortise Prep Length

1.Locate the Prep: The "prep" is the rectangular cutout in the edge of the door where the latchbolt protrudes. You may need to retract the latch by pushing the touchpad to see its full size.

2.Measure the Mortise Length: Carefully measure the length of this cutout (horizontally). Common lengths are 16", 18", 22", 24", 26", 30", 36", 42", and 48". This measurement is the primary factor in determining the device size.

3.Measure the Mortise Depth and Height: Also note the depth (how far back the pocket goes into the door) and the height of the cutout. While more standardized, these are good to verify.

4.Measure the Faceplate: Measure the visible metal faceplate on the edge of the door. Its length will typically correspond to the mortise prep.

Pro Tip: The model number of the existing device is often stamped on the inside of the mechanism. If you can safely remove the touchpad or endcap, you might find it, saving you from having to measure altogether.

Step 4: How to Measure a Surface Vertical Rod Device

These are the most complex to measure due to the rods.

The Critical Dimensions: Crossbar Length & Rod Centers

1.Measure the Crossbar Length: Just like with a rim device, measure the overall length of the main crossbar body.

2.Measure the Rod Centers (Most Important Step):

· For a device with top and bottom rods, measure from the center of the top rod hole to the center of the bottom rod hole.

· This measurement is absolutely critical. If it's off by even a small amount, the rods will not align with the latches at the top and bottom of the door.

3.Measure the Rod Length: If replacing rods, measure their full length from end to end.

4.Note the Latch Type: Identify if the top and bottom latches are mortise or surface mounted, as this will determine what parts you need to order.

Additional Measurements and Considerations

· Door Handing: Is the door left-hand or right-hand? And does it swing in or out? Stand on the secure side (the side where you need a key to enter). If the hinges are on the left, it's a left-hand door. If they are on the right, it's a right-hand door.

· Door Material and Thickness: Is the door wood, metal, or glass? Metal doors are often thicker than wood doors. Glass doors require special brackets.

· Function: What is the device's function? Fire exit only, dogged operation (stays unlocked), or equipped with a key cylinder? Note any special features like a push-to-lock button or alarm integrated into the device.

When in Doubt, Call a Professional

While this guide provides a solid foundation, door hardware can be complex. If your measurements seem non-standard, the device is very old, or you are unsure about any step, do not guess. The safest and most reliable course of action is to contact a licensed door hardware consultant or locksmith. They have the expertise to ensure your exit device is measured, supplied, and installed correctly, guaranteeing the safety of the building's occupants and full compliance with all regulations.

Measuring an exit device is a meticulous but manageable task. By following this step-by-step guide for your specific device type, you can ensure you get the right part every time, keeping your building safe, secure, and up to code.

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