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Chimney Measurement Toolkit
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1234 Cool Dr #2026-001

Chase Cover

Precision:
Edit direction:
Left side is fixed. Right side adjusts when you edit.

Additional Notes:

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Price Estimator

Outside Mount

Outside Mount Cap

Precision:

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Fireplace

Fireplace Measurement

Front View
Side View

Measurements:

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Fireplace Opening
Back Wall & Width
Mantle, Trim & Hearth
Hearth & Floor
Top Depth & Flue

Flue Size Calculator

Fireplace Opening

Code Ratios

Round flue: min 1/12 of opening area (8.33%)
Square flue: min 1/10 of opening area (10%)
Rectangular (under 2:1): min 1/10 of opening area (10%)
Rectangular (2:1 or more): min 1/8 of opening area (12.5%)
Per IRC R1003.15 / NFPA 211 §11.2.2. Based on minimum chimney height — taller chimneys may allow smaller flues per IRC Table R1003.15.

Liner Sizing Calculator

Per NFPA 211 §4.1. Size by appliance collar or BTU output. Use 10:1 ratio for chimneys under 25 ft, 12:1 for 25 ft or taller.

Liner Material Guide
316Ti / 316L Stainless: Required for wood, pellet, coal (acidic flue gases)
304 Stainless: Suitable for gas and oil (less corrosive exhaust)
AL29-4C: Premium alloy — all fuel types, lifetime warranty typical
Insulation: Required for solid fuel; recommended for gas/oil to reduce condensation

Ovalization Calculator

Will a round flex liner fit your flue tile? Enter the tile opening and liner size to check.

Common Clay Flue Tile Sizes (nominal → actual inside)
8" × 8"
→ 6.5" × 6.5"
8" × 12"
→ 6.5" × 10.5"
12" × 12"
→ 10.5" × 10.5"
12" × 16"
→ 10.5" × 14.5"
16" × 16"
→ 14.5" × 14.5"
16" × 20"
→ 14.5" × 18.5"
Actual dimensions vary by manufacturer. Always measure the inside opening.

3-2-10 Rule Calculator

Per IRC R1003.9: Chimneys shall extend not less than 3 ft above the highest point where the chimney passes through the roof, and not less than 2 ft higher than any portion of the building within 10 ft (horizontal).

2021 International Residential Code — Chapter 10: Chimneys and Fireplaces. "Any portion of a building" includes ridges, dormers, walls, and other structures — not just the roof surface.

Your Measurements

High side of roof to chimney top
/ 12
"Along the roof" = measured with a tape on the shingles

Common Pitches

4/12 — 18.4° — Low slope
6/12 — 26.6° — Standard
8/12 — 33.7° — Moderate steep
10/12 — 39.8° — Steep
12/12 — 45° — Very steep

How to Find Roof Pitch Manually

Method 1: Level + Tape Measure (Most Accurate)

This is the go-to method most pros use. You need a 12-inch level (or any level) and a tape measure.

1. Place the level on the roof surface so one end touches the shingles.
2. Hold it level (bubble centered) — the other end will be floating above the roof.
3. Measure 12 inches along the level from the end touching the roof.
4. At that 12-inch mark, measure straight down to the roof surface.
5. That measurement in inches is your pitch. If it's 6 inches → 6/12 pitch.
Method 2: From the Attic

If you can get in the attic, you can measure the pitch on a rafter without going on the roof.

1. Hold a level against the bottom of a rafter.
2. Measure 12 inches along the level from where it touches the rafter.
3. Measure straight up from that point to the rafter. That's your pitch.
Method 3: Speed Square

A speed square (rafter square) has pitch markings built right in.

1. Place the lip of the speed square on the roof edge or a rafter.
2. Let a plumb bob or level hang from the pivot point.
3. Read the pitch directly off the scale on the square.
Method 4: From the Ground

If you can see the gable end of the house, you can estimate from the ground.

1. Stand back and take a photo of the gable end straight-on.
2. On the photo, measure the horizontal run from the eave to directly below the ridge.
3. Measure the vertical rise from the eave line to the ridge. Divide rise by run and multiply by 12.
Pro Tip
The level method on the roof is the fastest and most accurate. Keep a small torpedo level in your truck — it takes 30 seconds. If you don't have a level, many free phone apps can act as a level too.

Code Reference

2021 IRC R1003.9 — Termination (Masonry Chimneys):
"Chimneys shall extend not less than 2 feet (610 mm) higher than any portion of a building within 10 feet (3048 mm), but shall be not less than 3 feet (914 mm) above the highest point where the chimney passes through the roof."
IRC R1005.1 — Factory-Built Chimneys:
Must be installed and terminated per the manufacturer's installation instructions. Most manufacturers also require the 3-2-10 rule as a minimum.
NFPA 211 — Standard for Chimneys, Fireplaces, Vents:
Also specifies the same 3-2-10 height requirements for solid-fuel appliances.
Disclaimer
This tool is a field reference only. It calculates based on roof slope and does not account for dormers, adjacent structures, second stories, or other building features that may be within the 10-ft horizontal zone. Always verify compliance with local building codes and consult a certified chimney professional or building inspector for final determination. Local jurisdictions may have adopted different editions of the IRC or additional requirements.

Additional Tools

Chimney Cricket Calculator

Per IRC R1003.20: Crickets required when chimney width parallel to ridgeline is more than 30 inches.

Table R1003.20 — Cricket Height (H) by Roof Slope:
12/12 = 1/2 of W  |  8/12 = 1/3 of W  |  6/12 = 1/4 of W  |  4/12 = 1/6 of W  |  3/12 = 1/8 of W

Area Calculator

Calculate square inches for common chimney shapes.

Unit Converter

Convert between inches, feet, millimeters, and centimeters.

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Clearances to Combustibles

Quick reference per IRC R1001.11 / R1003.18 and NFPA 211 §7.3, §11.2.

Masonry Fireplace
Front & sides to framing
2"
Back to framing
4"
Trim/mantle from opening
6" min
Projecting mantle (more than 1.5")
12" min from opening
Trim projection rule
1/8" per inch of distance
Masonry Chimney
Interior chimney to combustibles
2"
Exterior-only chimney
1"
Trim/sheathing may abut if
12" from firebox lining
Hearth Extension
Front (under 6 sq ft opening)
16"
Front (6 sq ft or larger)
20"
Sides (under 6 sq ft opening)
8"
Sides (6 sq ft or larger)
12"
Stovepipe / Connectors
Single wall to walls
18"
Single wall to ceiling
18"
Double wall to walls
6"
Double wall to ceiling
8"
Class A chimney pipe
2"
Solid Fuel Appliances
Unlisted stove — sides & back
36"
Unlisted stove — front
36"
Unlisted stove — top to ceiling
48"
Floor protection (legs over 6")
18" all sides
Listed stove — per manufacturer
Check listing
Always check manufacturer specs
Listed appliances may have reduced clearances per their testing. Manufacturer instructions always take precedence. Local codes may differ.
Integrations

Connect Your Tools

Link Chimeasure with your field service software to sync jobs and measurements.

Jobber
Sync jobs, clients & measurements
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Workiz
Sync jobs & measurements
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Paste your Workiz API Token from Settings → Developer API
Housecall Pro
Coming soon
ServiceTitan
Coming soon
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Make sure all dimensions are correct before exporting. This document may be used for fabrication or compliance.

ChimChat — Insert Finder

Searching for inserts that fit your opening...
Analyzing your measurements against
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