1. What is Make-up Air CFM?

Make-up Air CFM (Cubic Feet per Minute) refers to the amount of outdoor air that must be introduced into a building to replace air being exhausted by ventilation systems, maintaining proper air balance and building pressure.

2. How Does the Calculator Work?

The calculator uses the make-up air formula:

Where:

• \( \text{Exhaust CFM} \) — Total air being exhausted from the building (ft³/min)
• \( \text{Building Pressure Adjustment} \) — Additional air needed for positive/negative pressure control (cfm)
• \( \text{Make-up CFM} \) — Total make-up air required (ft³/min)

Explanation: This calculation ensures proper ventilation balance by accounting for both exhaust requirements and building pressure needs.

3. Importance of Make-up Air Calculation

Details: Proper make-up air calculation is essential for maintaining indoor air quality, preventing negative pressure issues, ensuring ventilation system efficiency, and complying with building codes and standards.

4. Using the Calculator

Tips: Enter exhaust CFM in ft³/min and building pressure adjustment in cfm. Exhaust CFM must be ≥0, while adjustment can be positive (for positive pressure) or negative (for negative pressure).

5. Frequently Asked Questions (FAQ)

Q1: What happens if make-up air is insufficient?
A: Insufficient make-up air can cause negative pressure, leading to backdrafting, difficulty opening doors, and poor indoor air quality.

Q2: How do I determine exhaust CFM?
A: Exhaust CFM is calculated by summing the CFM ratings of all exhaust fans, range hoods, bathroom fans, and other ventilation equipment in the building.

Q3: What is building pressure adjustment?
A: This accounts for additional air needed to maintain desired building pressure - positive for clean rooms, negative for containment areas, or neutral for most applications.

Q4: Are there code requirements for make-up air?
A: Yes, most building codes require make-up air systems when exhaust exceeds certain thresholds to maintain proper ventilation balance.

Q5: Can make-up air affect energy efficiency?
A: Yes, properly designed make-up air systems with heat recovery can significantly improve energy efficiency by preconditioning incoming air.