Chimney Chase Cover Measurement Tool

Use this chimney chase cover measurement tool to record the finished cover size and locate the flue opening. Enter the measurements in consistent units, keep the cover oriented the same way, and review the calculated diagram before sending dimensions to your fabricator.

Using the chimney chase cover measurement tool

Measure the flat finished top from edge to edge for its length and width. Leave the skirt out of those two measurements. Mark the north side on the cover so the north, south, east and west gaps stay attached to the correct edges when you enter them.

For each gap, measure from the outside edge of the cover to the nearest outside wall of the flue pipe. Keep the tape on the same surface of the pipe for all four readings. Do not substitute the storm collar, rain cap or sealant bead for the pipe wall. The tool uses the opposing gaps to calculate the opening diameter; it does not require you to reach over the flue or estimate its center.

Check the chimney chase cover measurement tool diagram

The horizontal check is cover length minus the west and east gaps. The vertical check is cover width minus the north and south gaps. Both calculations should produce the same diameter for a round opening. For example, a 60 by 40 inch cover with 16 inch west and east gaps and 6 inch north and south gaps gives a 28 inch opening in both directions. If the checks disagree, recheck the cover dimensions, orientation and each gap before relying on the drawing.

The center view is calculated from the west and north measurements. Switch between the edge-gap view and center view to make the layout easier to discuss with the fabricator. The diagram shows measured geometry only: it does not add cutting clearance, account for fabrication tolerances or decide how the cover should be attached.

What to confirm with your fabricator

Send the finished top dimensions, all four edge gaps, the pipe outside diameter and the diagram together. Ask the fabricator to confirm the finished cutout diameter, required clearance, material, skirt dimensions and any collar details for the specific installation. Check whether the shop wants fractions or decimal dimensions and label the north side clearly on your notes. A screenshot is useful for communication, but verify the final measurements and fabrication requirements with the person making the cover before ordering or cutting metal.

If your review uncovers damage around a flue or chimney, see our chimney repair service information for homeowners.

Instructions: 

1-256-ROOFERS · AUTOMATIC MEASUREMENT TOOL

Automatic chase cover diagram

Pipe diameter and center calculated from four outside-edge measurements

Leave the existing cover and flue assembled. Measure straight from each cover edge to the nearest outside wall of the exposed flue pipe. You do not need to reach or measure its center. The tool calculates the pipe diameter and center from all four gaps.

1. Finished cover top

Use the finished top dimensions, excluding the skirt. Mark the North side on the actual cover.

2. Locate the flue opening

Measurement reference: outside wall of the flue pipe. Keep all four measurements on the same pipe surface. Do not use the wider storm collar, cap, or sealant edge as the pipe diameter.

East and South distances (required)

Accepts 12, 12.5, 12 1/2, 12-1/2 or 12½.
Orange circle: flue pipe outlineNo clearance added automatically
Skirt and collar heights
Top view from above. Center measurements are calculated for the fabricator; you do not measure to the center in the field. The circle shows the pipe outside diameter. Confirm the finished cutout diameter and any extra clearance with the fabricator.