Calculate Cfm

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CFM (Cubic Feet per Minute) Sizing Calculator

Bedroom (4 ACH) Living Room (6 ACH) Bathroom (8 ACH) Kitchen (15 ACH) Commercial Kitchen / Workshop (20 ACH) Basement (2 ACH)

ACH determines how many times the air is completely replaced every hour.

Required Airflow

Cubic Feet per Minute (CFM)

function calculateCFM() { var length = parseFloat(document.getElementById('roomLength').value); var width = parseFloat(document.getElementById('roomWidth').value); var height = parseFloat(document.getElementById('roomHeight').value); var ach = parseFloat(document.getElementById('achValue').value); if (isNaN(length) || isNaN(width) || isNaN(height) || length <= 0 || width <= 0 || height <= 0) { alert('Please enter valid dimensions for the room.'); return; } var volume = length * width * height; var cfm = (volume * ach) / 60; document.getElementById('cfm-result-container').style.display = 'block'; document.getElementById('cfm-output').innerHTML = Math.round(cfm) + " CFM"; document.getElementById('volume-output').innerHTML = "Total Room Volume: " + volume.toLocaleString() + " cubic feet"; }

What is CFM and Why Does It Matter?

CFM stands for Cubic Feet per Minute. It is a measurement of the velocity at which air flows into or out of a space. In the HVAC industry, CFM is the gold standard for determining the size of fans, air purifiers, and ventilation systems required to maintain air quality and temperature.

The CFM Formula

To calculate the CFM needed for a specific room, use the following formula:

CFM = (Volume of Room × ACH) / 60

  • Volume of Room: Length × Width × Ceiling Height (in feet).
  • ACH (Air Changes per Hour): How many times you want the air in the room to be replaced with fresh or filtered air every hour.
  • 60: Converts the hourly rate into minutes.

Standard ACH Guidelines

Different rooms require different levels of ventilation. Below are industry-standard Air Changes per Hour (ACH) for common spaces:

Room Type Recommended ACH
Bedrooms / Living Rooms 4 – 6 ACH
Bathrooms 8 – 10 ACH
Kitchens 15 – 20 ACH
Workshops / Garages 20 – 30 ACH

Example Calculation

Imagine you have a living room that is 20 feet long, 15 feet wide, and has 10-foot ceilings. You want standard ventilation (6 ACH).

  1. Calculate Volume: 20 × 15 × 10 = 3,000 cubic feet.
  2. Apply ACH: 3,000 × 6 = 18,000 cubic feet per hour.
  3. Convert to Minutes: 18,000 / 60 = 300 CFM.

In this scenario, you would need an HVAC system or fan capable of moving at least 300 CFM to properly ventilate that space.

Factors That Affect CFM Requirements

While the basic formula provides a solid estimate, several real-world factors can influence the actual CFM you need:

  • Duct Friction: If the air has to travel through long or winding ducts, you will need a higher CFM rating to overcome the resistance (static pressure).
  • Occupancy: Rooms with more people generally require higher ventilation to maintain CO2 levels.
  • Equipment: Kitchens with gas stoves or workshops with chemicals require significantly higher ACH to remove pollutants safely.
  • Filter Density: If you are using high-efficiency filters (like HEPA), they create more resistance, meaning you might need a more powerful motor to maintain the same CFM.

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