What size flue do I need — and what will chimney repair, relining, a sweep or an install cost?
Free, no-signup calculators for homeowners, DIYers and small masons or sweeps planning, sizing, repairing, relining, cleaning, inspecting or installing a masonry or factory-built chimney and its fireplace, insert or wood stove — figure out what size flue or liner you need (the timeless 1/10 rule and the 3-2-10 height rule), how much a repair, reline, sweep, inspection or install costs, all on the dimensions you measure and the prices you enter, with the formula, a worked example and a reference chart on every tool.
Example: a 30 in × 29 in masonry fireplace opening is 870 in², so by the 1/10 rule the flue must be at least 72.5 in² if it’s round — a 10-inch round liner — or at least 87 in² if it’s rectangular, a nominal 12×12 clay tile. Measure the opening, and always round up.
Start here: what size flue your fireplace needs (round area ≥ 1/12 of the opening, rectangular ≥ 1/10), the 3-2-10 chimney-height rule, flue-liner size by appliance, round↔rectangular flue area, wood-stove flue size, theoretical draft, and chimney-cap size — from the dimensions you measure.
Budget the fix: chimney repair, rebuild, crown repair, tuckpointing by the linear foot, brick / spalling repair, flashing, chimney-leak and firebox repair — on the materials, labor and access prices you enter from your own quotes.
Budget the service: chimney sweep, cleaning by condition, creosote removal by stage, and an NFPA 211 Level 1/2/3 inspection — the labor and access you enter, scaled by labeled condition and creosote-stage multipliers.
Budget the liner: chimney-liner cost by length and rate, relining cost, stainless-steel liner by diameter and length, a clay-vs-stainless-vs-cast selector, and the liner length from your chimney height — prices you enter.
Budget the install: fireplace, insert, gas-fireplace and wood-stove installation, a new masonry or factory-built chimney by height, and a chimney-cap install — on the unit, venting, labor and add-on prices you enter.
Plan & understand: creosote buildup stages 1–3, the NFPA 211 inspection-level reference, clearance-to-combustibles, a chimney anatomy / parts glossary, a damper-types reference, a cord-wood / BTU reference, and how to measure flue size.
No calculator matches that. Try “flue size”, “repair”, “liner” or “sweep”.
Built for the whole chimney job — and to stay correct forever
ChimneyCalcs gathers the calculations homeowners, DIYers and small masons or sweeps reach for around a chimney and its hearth appliance — what size flue or liner you need (a round flue must be at least 1/12 of the fireplace opening, a rectangular one at least 1/10; a liner matches the appliance outlet), how tall the chimney must be (the NFPA 211 3-2-10 rule — the top at least 3 ft above where it passes through the roof and 2 ft above anything within 10 ft), and what a repair, reline, sweep, inspection or install will cost — sizing → repair → sweep → reline → install, in one focused hub, in US units, without signup, with transparent formulas. Every tool shows not just the answer but the underlying formula, a worked example and a reference table.
Because the tools rest on timeless flue geometry (opening area = width × height; round flue area = opening ÷ 12; rectangular = opening ÷ 10; circle area A = π·(d/2)²; round diameter d = 2·√(A/π); the 3-2-10 height rule as a max() of two clearances) and cost arithmetic (cost = materials + labor + access, ×(1 + contingency)), plus stable, labeled conventions (the flue-size rule, standard clay-tile sizes, liner-by-appliance, creosote stages, NFPA 211 inspection levels, clearance-to-combustibles, cost bands), they stay correct with no maintenance — no live material or labor rate, no regional price database, no product catalog, no sweep or mason directory. Cost tools use the prices you enter from your own quotes and bills; labeled cost bands are only a sanity guide. More at Sources & formulas, Methodology and About.
How to pick the right tool
Three quick paths. If you are planning a fire or a reline, start in Sizing & Draft: measure the fireplace opening and read the required flue, or match a liner to your stove’s outlet. If you are facing a repair or a quote, go straight to Repair & Masonry Cost or Relining & Liner Cost and enter the materials, labor and access from the estimate to sanity-check the total. If you are keeping a chimney safe, use Sweep, Cleaning & Inspection for the service cost and the Planning & Reference section for the creosote stages, the NFPA 211 inspection levels and the clearances — then have a CSIA-certified sweep confirm what you find.
Estimates, not bids. Every result is a planning estimate from your own prices, or a sizing / draft guide — not a bid, an installation procedure, or a combustion, chimney-fire, carbon-monoxide-medical, structural or code-compliance verdict. Get itemized written quotes from a CSIA-certified sweep and a licensed, insured mason; confirm your exact flue and opening dimensions, follow NFPA 211, the appliance manufacturer’s instructions and local code; and round flue area up to the nearest standard liner or tile.
Behind the site is Francesco Zinghinì, its author and curator — not a licensed chimney sweep or mason, but an engineer who builds deterministic calculators and verifies every formula numerically against known examples. Read the approach in the methodology.