Air Change Rate Calculator Uk

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Air Change Rate Calculator UK .ach-calculator-wrapper { font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif; max-width: 800px; margin: 20px auto; padding: 20px; border: 1px solid #e0e0e0; border-radius: 8px; background-color: #f9fbfd; color: #333; } .ach-calculator-wrapper h2 { text-align: center; color: #0056b3; margin-bottom: 20px; } .ach-form-group { margin-bottom: 15px; } .ach-form-group label { display: block; font-weight: 600; margin-bottom: 5px; color: #444; } .ach-row { display: flex; gap: 15px; flex-wrap: wrap; } .ach-col { flex: 1; min-width: 200px; } .ach-input, .ach-select { width: 100%; padding: 10px; border: 1px solid #ccc; border-radius: 4px; font-size: 16px; box-sizing: border-box; } .ach-input:focus { border-color: #0056b3; outline: none; } .ach-btn { width: 100%; padding: 12px; background-color: #0056b3; color: white; border: none; border-radius: 4px; font-size: 16px; font-weight: bold; cursor: pointer; margin-top: 10px; transition: background 0.2s; } .ach-btn:hover { background-color: #004494; } .ach-results { margin-top: 25px; padding: 20px; background-color: #ffffff; border: 1px solid #ddd; border-radius: 4px; display: none; } .ach-result-item { margin-bottom: 15px; padding-bottom: 15px; border-bottom: 1px solid #eee; } .ach-result-item:last-child { border-bottom: none; margin-bottom: 0; } .ach-label { font-size: 14px; color: #666; } .ach-value { font-size: 24px; font-weight: bold; color: #0056b3; } .ach-sub-value { font-size: 14px; color: #888; } .ach-note { font-size: 13px; color: #666; background: #eef6ff; padding: 10px; border-radius: 4px; margin-top: 10px; } .ach-content { margin-top: 40px; line-height: 1.6; } .ach-content h3 { color: #333; margin-top: 20px; } .ach-content ul { padding-left: 20px; } .ach-content li { margin-bottom: 8px; } .ach-table { width: 100%; border-collapse: collapse; margin: 15px 0; } .ach-table th, .ach-table td { border: 1px solid #ddd; padding: 8px; text-align: left; } .ach-table th { background-color: #f2f2f2; }

Air Change Rate Calculator (UK)

Cubic Meters per Hour (m³/h) Litres per Second (l/s) Cubic Feet per Minute (CFM)
Standard UK recommendation for offices/shops is often 4-6 ACH.
Room Volume
0 m³
Current Air Change Rate (ACH)
0 ACH
Time to replace air: 0 minutes
Required Airflow to meet Target
0 m³/h
0 l/s
Calculations based on standard air density. Ensure fans are rated for the static pressure of your ductwork.

Understanding Air Change Rates in the UK

The Air Change Rate, often denoted as ACH (Air Changes per Hour), is a critical metric in building ventilation, HVAC design, and indoor air quality management. It represents the number of times the total volume of air within a room is removed and replaced with fresh (or filtered) air in one hour.

In the United Kingdom, ventilation requirements are governed by Building Regulations Part F. Maintaining adequate ACH is essential for removing stale air, moisture (preventing damp and mould), odours, and airborne pathogens (such as COVID-19 or flu viruses).

How to Calculate ACH

The formula for calculating Air Changes per Hour is relatively straightforward, provided you have consistent units. The calculator above performs these conversions automatically.

The Formula:
ACH = Air Flow Rate (m³/h) ÷ Room Volume (m³)

Where:

  • Room Volume (m³) = Length (m) × Width (m) × Height (m)
  • Air Flow Rate = The volume of air moved by your fan or ventilation system.

Unit Conversions Common in the UK

Ventilation equipment in the UK is often rated in Litres per Second (l/s) or Cubic Meters per Hour (m³/h). Occasionally, imported units may use CFM (Cubic Feet per Minute).

  • To convert l/s to m³/h: Multiply by 3.6
  • To convert CFM to m³/h: Multiply by 1.699

Typical UK Recommended Air Change Rates

Room Type / Application Recommended ACH
Residential Living Rooms 4 – 6
Kitchens 15 – 20 (or specific extraction rates)
Bathrooms 6 – 10 (or specific extraction rates)
Offices 4 – 6
Warehouses 2 – 4
Classrooms 4 – 6
Server Rooms 20 – 30+ (for cooling)

Why is ACH Important?

1. Mould and Damp Prevention:
UK homes are prone to condensation. A low ACH means moisture from cooking, bathing, and breathing stays trapped, leading to black mould growth on cold surfaces.

2. Health and Safety:
Higher air change rates dilute airborne contaminants, including viruses, allergens, and VOCs (Volatile Organic Compounds) from furniture and cleaning products.

3. Comfort:
Proper ACH prevents stuffiness and regulates temperature, ensuring a comfortable environment for occupants.

function calculateAirChange() { // 1. Get Inputs var len = parseFloat(document.getElementById('roomLength').value); var wid = parseFloat(document.getElementById('roomWidth').value); var hgt = parseFloat(document.getElementById('roomHeight').value); var currentFlow = parseFloat(document.getElementById('currentFlow').value); var flowUnit = document.getElementById('flowUnit').value; var targetACH = parseFloat(document.getElementById('targetACH').value); // Validation if (isNaN(len) || isNaN(wid) || isNaN(hgt) || len <= 0 || wid <= 0 || hgt 0) { showCurrent = true; // Convert to m3/h if (flowUnit === 'm3h') { flowM3H = currentFlow; } else if (flowUnit === 'ls') { flowM3H = currentFlow * 3.6; } else if (flowUnit === 'cfm') { flowM3H = currentFlow * 1.69901; } // Calculate ACH currentACH = flowM3H / volume; } // 4. Calculate Required Flow for Target ACH var reqFlowM3H = 0; if (!isNaN(targetACH) && targetACH > 0) { reqFlowM3H = volume * targetACH; } // 5. Display Results var resultDiv = document.getElementById('achResults'); resultDiv.style.display = 'block'; // Volume document.getElementById('resVolume').innerText = volume.toFixed(2) + " m³"; // Current ACH var currentSection = document.getElementById('currentAchSection'); if (showCurrent) { currentSection.style.display = 'block'; document.getElementById('resCurrentACH').innerText = currentACH.toFixed(2) + " ACH"; // Time to replace air (60 mins / ACH) var minsToReplace = 60 / currentACH; document.getElementById('resTimeReplace').innerText = "Complete air replacement every " + minsToReplace.toFixed(1) + " minutes"; } else { currentSection.style.display = 'none'; } // Required Flow document.getElementById('resReqFlowM3').innerText = reqFlowM3H.toFixed(0) + " m³/h"; // Convert required flow to l/s for reference var reqFlowLS = reqFlowM3H / 3.6; document.getElementById('resReqFlowLS').innerText = reqFlowLS.toFixed(0) + " l/s (Litres per second)"; // Add specific advice based on result var note = document.getElementById('achNote'); if (showCurrent && currentACH < targetACH) { note.innerHTML = "Warning: Your current system (" + currentACH.toFixed(2) + " ACH) does not meet your target of " + targetACH + " ACH. You need to increase airflow."; note.style.backgroundColor = "#fff3cd"; note.style.color = "#856404"; } else if (showCurrent && currentACH >= targetACH) { note.innerHTML = "Success: Your current ventilation meets or exceeds the target requirement."; note.style.backgroundColor = "#d4edda"; note.style.color = "#155724"; } else { note.innerHTML = "Result shows the fan rating required to achieve " + targetACH + " air changes per hour in this room."; note.style.backgroundColor = "#eef6ff"; note.style.color = "#666"; } }

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