Engineer stack diameters using flow, velocity, and loss factors in minutes today. Built for planners needing quick exports, clear formulas, and practical guidance onsite.
Friction factor is an engineering approximation for early sizing. For rough ducts, high temperatures, or special fittings, use a detailed method and manufacturer data.
Tip: If pressure drop is high, increase diameter or reduce elbows. If height is constrained, coordinate early with safety and local requirements.
| Case | Q (m³/s) | vmax (m/s) | L (m) | Elbows | K each | Diameter (mm) | ΔP (Pa) | Height (m) |
|---|---|---|---|---|---|---|---|---|
| Generator exhaust | 1.20 | 12 | 18 | 2 | 0.9 | 357 | ~106 | 13 |
| Temporary ventilation | 0.60 | 10 | 24 | 4 | 1.1 | 277 | ~241 | 9 |
| Boiler flue draft | 0.90 | 14 | 12 | 1 | 0.7 | 286 | ~55 | 11 |
Example outputs are illustrative. Your results will vary with density, viscosity, and fitting losses.
Stack sizing supports temporary ventilation, generator exhaust routing, dust extraction, and process discharge on active sites. The goal is to move a required flow rate while controlling velocity, noise, and pressure losses so fans or equipment can operate within their performance curves.
Begin with the design flow rate and a practical maximum velocity. Higher velocity reduces diameter but increases losses, noise, and vibration risk. Many projects start with 8–15 m/s for general exhaust and then refine after checking fan capacity and acoustic constraints.
The calculator uses continuity to compute area and diameter. This step is intentionally transparent: if you double flow at the same velocity limit, the required area doubles and diameter grows by about the square root of two. This relationship is useful for quick option studies.
Pressure loss is estimated with Darcy–Weisbach plus a minor-loss term. Straight length produces friction loss, while fittings add losses through K values. Because temporary stacks may include elbows, reducers, and rain caps, capturing minor losses improves early feasibility checks.
Reynolds number indicates whether flow is laminar or turbulent. For most construction exhaust applications, the regime is turbulent, and a smooth-pipe approximation provides a reasonable first pass. If roughness is significant, replace the friction factor with a more detailed method.
A taller discharge point helps reduce re-entrainment into work areas and nearby intakes. This tool recommends a conservative height based on building height plus a clearance margin, while respecting a minimum stack height requirement set by your site plan or safety rules.
Example input set: Q = 1.20 m³/s, vmax = 12 m/s, L = 18 m, ρ = 1.20 kg/m³, μ = 1.8e−5 Pa·s, elbows = 2, K each = 0.9, building height = 10 m, clearance = 3 m. The computed diameter is about 357 mm and total loss is near 106 Pa.
After sizing, confirm that the selected diameter is available, check support spacing and thermal expansion, and verify equipment backpressure limits. Finally, document assumptions, then export the CSV or PDF for reviews. Field changes should trigger a quick recalculation. If unsure, consult the equipment datasheet and local emission or safety requirements first.
It estimates stack diameter from flow and a velocity limit, then reports area, Reynolds number, friction factor, and an approximate pressure drop including minor losses.
Use m³/s when you already have SI flow. Use CFM when readings come from fan schedules or rental equipment sheets; the tool converts CFM to m³/s automatically.
Pick a velocity that balances diameter, noise, and loss. Start around 8–15 m/s for general exhaust, then adjust if the calculated pressure drop exceeds available fan static pressure.
These properties affect Reynolds number and dynamic pressure, which influence friction factor and pressure loss. Use values matching your gas temperature and composition for better results.
They are a planning approximation. Real K depends on elbow radius, transitions, and attachments. If fittings are complex, sum multiple K values or use manufacturer loss coefficients.
No. Height guidance is conservative and helps reduce re-entrainment, but compliance depends on local regulations, dispersion, fire safety, and project specifications. Confirm requirements before installation.
Yes, as supporting documentation. Include the exported CSV or PDF with assumptions, equipment ratings, and any field constraints so reviewers can validate sizing decisions.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.