Sources & formulas

Every calculator on ChimneyCalcs rests on established flue geometry plus stable chimney conventions. Unlike topics with a time dependency, “verification” here is mathematical: each formula is tested against known values and is therefore correct for good. Here are the technical foundations by area.

Identities & geometry

  • Opening area: opening (in²) = width × height.
  • The 1/10 rule: round flue area ≥ opening ÷ 12; rectangular flue area ≥ opening ÷ 10.
  • Circle: area A = π·(d/2)²; round diameter d = 2·√(A/π); equivalent square side = √A.
  • Liner: liner/flue cross-section ≥ appliance outlet area; round up to the next standard size.
  • 3-2-10 height rule (NFPA 211): chimney top = max(roof penetration + 3 ft, tallest point within 10 ft + 2 ft).
  • Theoretical draft: ΔP ≈ 0.0342 · B · H · (1/T_out − 1/T_in), T in °R = °F + 460 (LABELED indicative).
  • Liner length: length = ceil(chimney height + termination overhang).
  • Cost: (materials + labor + access − discount) ×(1 + contingency); masonry quantities by linear foot (tuckpointing), square foot (crown) and foot of height (liner).

Convention typicals (labeled)

  • Flue size by opening & standard clay-tile sizes: the 1/10–1/12 rule with the nearest 8×8 … 16×16 nominal tile — labeled, confirm your exact dimensions.
  • Liner by appliance: a modern wood stove ~6", larger ~7–8" — labeled, match the outlet.
  • Creosote stages 1–3: loose soot, hard flaky, glazed tar-like (the highest chimney-fire risk) — labeled.
  • NFPA 211 inspection Levels 1–3: routine visual, camera scan on a sale/change, opening concealed areas — labeled.
  • Clearance-to-combustibles, cost bands, contingency ~10%: labeled planning typicals, set by the listing and local code.

Primary references (public bodies)

  • NFPA — the National Fire Protection Association, publisher of NFPA 211 (chimneys, fireplaces, vents and solid-fuel-burning appliances), the basis of the 3-2-10 height rule and the inspection Levels.
  • Chimney Safety Institute of America (CSIA) — sweep certification, creosote and inspection guidance.
  • U.S. EPA Burn Wise — wood-burning appliance and efficiency guidance.
  • Local building department (AHJ) — the authority having jurisdiction sets the code that applies to your chimney.

Cost tools

  • Every cost tool uses the prices you enter (materials $, labor $, access $, $/linear foot, $/foot) — no material or labor rate is stored, so the site needs no maintenance. Cost bands are a labeled sanity guide.
  • Quote check: the tools compare your quoted numbers against a labeled band by job — a sanity flag, not a bid.

Material, labor and service prices, product specifications and local rules vary by place and change over time — always confirm your exact flue and opening dimensions, follow NFPA 211, the appliance manufacturer’s instructions and local code, round flue area up to the nearest standard liner or tile, defer creosote, chimney fire, carbon monoxide, structural and code judgement to a certified professional, and get itemized written quotes from a CSIA-certified sweep and a licensed, insured mason before you commit.