Advanced Broan Make-Up Air Calculator

Formula Used

The calculation model evaluates total exhaust air volume by summing the primary range hood capacity and secondary household exhaust ratings. When this aggregate value surpasses the regulatory threshold of 400 CFM, a make-up air requirement is triggered. The net compensated volume is derived by taking the difference between total exhaust and the standard threshold, adjusted according to house tightness coefficients and duct friction loss metrics.

How to Use This Calculator

1. Input your primary kitchen range hood rating in cubic feet per minute.
2. Add any supplementary bathroom or utility exhaust fan ratings into the secondary field.
3. Specify your estimated duct run length and choose your structural parameters.
4. Select your preferred climate zone and damper configuration type.
5. Click the calculate button to review your precise airflow requirements instantly.

Understanding Make-Up Air Systems

Modern residential properties are constructed with high-efficiency insulation and tight weatherproofing envelopes. While this design optimizes energy performance, it creates significant challenges when powerful kitchen ventilation appliances operate. High-capacity range hoods exhaust massive volumes of indoor air rapidly. Without an intentional replacement pathway, negative pressure builds up inside the dwelling space.

Preventing Backdrafting Hazards

Negative indoor pressure creates severe safety risks by drawing combustion gases backward through flues and chimneys associated with natural gas water heaters, furnaces, and fireplaces. This dangerous phenomenon, known as backdrafting, introduces toxic carbon monoxide directly into living spaces. Installing a properly sized make-up air system equalizes interior and exterior pressures seamlessly, protecting occupants from invisible health hazards.

Regulatory Building Codes

Building codes across numerous jurisdictions now strictly mandate make-up air systems for any kitchen exhaust system exceeding specific thresholds, typically set at 400 CFM. Compliance inspectors check for integrated interlock systems that automatically open fresh air dampers whenever the kitchen hood operates. Using advanced calculation tools ensures your project meets or exceeds all regional safety guidelines without costly guesswork.

Frequently Asked Questions

What happens if I ignore make-up air requirements?
Ignoring requirements can lead to failed building inspections, smoke spillage from cooking appliances, and dangerous backdrafting of combustion gases.

Are powered units better than passive dampers?
Powered units actively push tempered air indoors, whereas passive systems rely on negative pressure to draw air through an automated interlocked damper.

How do I find my range hood CFM rating?
Check the manufacturer specification label located inside the hood canopy housing or consult your original user manual documentation.