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Air Changes per Hour Calculator – Ventilation & Cost

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Air Changes per Hour (ACH) Calculator – Ventilation Materials & Cost

ACH Calculator — Ventilation Materials & Cost

Size airflow by target ACH or reverse from known flow. Estimate diffusers, ducting, fans, and cost for India / US / UK.

Inputs
% extra on materials

Unit Rates (Editable)

Region: India (₹)
Edit for gauge & market.
Unit price; fan size check separately.
Sources & Rationale (tap to view)
  • Rates are indicative materials (no labor) — edit to suit supplier quotes in your region.

Please verify with your supplier.

Calculated Results
0 m³/h
0.0 Based on segment volumes
0.00 kW Assumes 250 Pa & η=55%
₹0
visual check
Methodology, Formulas & Unit Math

Core

  • ACH = (Q × 60) / V, where Q is airflow (m³/h) and V is room volume (m³).
  • Q = (ACH × V) / 60.
  • Volume V = L × W × H.
  • Round duct (suggested) diameter: D = √(4·q / (π·v)), where q is m³/s and v is design velocity (default 6 m/s supply branch).
  • Fan power (shaft) ≈ (Qm³/s × ΔP) / η. Defaults: ΔP=250 Pa, η=0.55.

Standards dropdown populates notes and typical targets. When a standard is chosen, a note appears: “Values derived from <Standard> (user must verify).”

More on airflow & ducts: Duct Design Calculator (ASHRAE) Ductwork via Bernoulli Pipe/Fittings Head-Loss Psychrometric Calculators

Air Changes per Hour (ACH) Calculator — What it is, how it works, and how to use it

A quick, practical way to size airflow, estimate materials & cost, and print a clean report.

What this calculator does

ACH tells you how many times a room’s air volume is replaced in one hour. This tool goes beyond the basic math:

  • Enter one or many segments (rooms/zones) with dimensions.
  • Choose a target ACH or use Reverse mode with a known flow.
  • SI / Imperial toggle with live conversions.
  • Standards dropdown (ASHRAE 62.1/62.2, CIBSE, NBC India) with safety notes.
  • Suggests round duct diameter, counts diffusers/grilles, and estimates materials & cost for India / US / UK (rates editable).
  • One-click HTML Report with KPIs, tables, and assumptions.

How it works (plain language)

  • Room volume V = L × W × H.
  • ACH ↔ Airflow:
    • Given ACH → Q: Q = ACH × V (m³/h).
    • Given flow → ACH: ACH = (Q × 60) / V.
  • Duct suggestion (round): with design velocity v, D = √(4·q / (π·v)), where q = Q/3600 (m³/s).
  • Devices: Diffusers & grilles = ceil(Q / capacity).
  • Costing: GI sheet area ≈ πD × run; flex ≈ 20% of run; + diffusers, grilles, dampers, fan, and a wastage %.
Methodology & unit math

Switching SI/Imperial converts inputs and outputs on the fly (m↔ft, m³/h↔CFM, etc.).

ACH = (Q × 60) / V
Q = (ACH × V) / 60
V = L × W × H
q = Q / 3600   (convert m³/h → m³/s)
D = sqrt( 4·q / (π·v) )
Fan power (shaft) ≈ (q_total × ΔP) / η   [default ΔP=250 Pa, η=0.55]

Standards dropdown shows a note: “Values derived from <Standard> (user must verify).”

How to use the calculator

  1. Pick Units: SI or Imperial.
  2. Choose a Standard (optional): ASHRAE 62.1/62.2, CIBSE, NBC India.
  3. Set Region Pricing: India / US / UK, edit rates as needed.
  4. Add Segments: name rooms; use Presets for quick ACH values.
  5. Enter Geometry: Length, Width, Height.
  6. Choose Mode:
    • Target ACH → compute Q, or
    • Known flow → compute ACH (reverse check).
  7. Refine: design velocity, estimated run length (or leave 0 to auto-estimate), device capacities.
  8. Review Results per segment and the KPIs at the bottom.
  9. Export/Import JSON for sharing; use Generate HTML Report for printing.

Name segments clearly (e.g., “Office – East”) so the report reads like a professional submittal.

Worked example — complete project

Scenario Small office suite, SI units, India pricing, wastage 5%, target ACH = 6. Device capacity defaults: 540 m³/h per diffuser and per return grille. Design branch velocity: 6 m/s.

Segment A — “Office – East”

  • Dimensions: L=8 m, W=5 m, H=3 m → V = 120 m³
  • Target ACH = 6 → Q = 720 m³/h (q = 0.20 m³/s)
  • Duct ⌀ with v=6 m/s: D = √(4·0.20/(π·6)) ≈ 0.206 m → round to 200–225 mm
  • Devices: diffusers ceil(720/540)=2, return grilles = 2, dampers = 2
  • Run length (auto): ~1.5×L = 12 m
  • GI sheet area: π×D×run ≈ 7.77 m²; Flex ≈ 2.4 m
ItemQtyRate (₹)Amount (₹)
GI duct sheet7.77 m²1100/m²8,543
Flexible duct2.4 m350/m840
Supply diffusers2500 each1,000
Return grilles2480 each960
Volume dampers2700 each1,400
Fan unit16,500 each6,500
Subtotal19,243
+5% allowance20,155

Segment B — “Meeting Room”

  • Dimensions: L=6 m, W=4 m, H=3 m → V = 72 m³
  • Target ACH = 6 → Q = 432 m³/h (q = 0.12 m³/s)
  • Duct ⌀ with v=6 m/s: D = √(4·0.12/(π·6)) ≈ 0.160 m → round to 160–180 mm
  • Devices: diffusers = 1, return grilles = 1, dampers = 1
  • Run length (auto): ~1.5×L = 9 m
  • GI sheet area: π×D×run ≈ 4.52 m²; Flex ≈ 1.8 m
ItemQtyRate (₹)Amount (₹)
GI duct sheet4.52 m²1100/m²4,976
Flexible duct1.8 m350/m630
Supply diffuser1500 each500
Return grille1480 each480
Volume damper1700 each700
Subtotal7,286
+5% allowance7,651
Total design airflow
1,152 m³/h
720 + 432
Weighted avg ACH
6
Q_total / V_total = 1,152 / 192
Fan power (est.)
0.145 kW
(q×ΔP)/η with q=0.32 m³/s, ΔP=250 Pa, η=0.55
Materials cost (est.)
₹27,806
20,155 + 7,651 (rounded)

Numbers are planning estimates. Adjust device capacities, run length, and unit rates for your project.

Load the sample into your calculator

  1. Click Download Sample JSON above.
  2. Open the calculator and press Import JSON.
  3. Select the downloaded ach_sample_project.json file.
  4. Review/modify anything (rates, capacities, runs), then generate your report.

The sample includes two segments (Office – East, Meeting Room), SI units, India pricing, and 5% allowance.

Helpful follow-ups

Disclaimer: This tool and article provide planning estimates only. Always verify requirements and final selections against the relevant standard and manufacturer data.

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