1. What is the Gas Furnace Flue Size Calculator?

The Gas Furnace Flue Size Calculator determines the appropriate diameter for furnace exhaust flues based on airflow (CFM) and velocity requirements. Proper flue sizing is essential for safe and efficient furnace operation.

2. How Does the Calculator Work?

The calculator uses the flue diameter formula:

Where:

• \( CFM \) — Cubic Feet per Minute (airflow rate)
• \( V \) — Velocity in feet per minute
• \( \pi \) — Mathematical constant (approximately 3.14159)

Explanation: The formula calculates the diameter needed to maintain proper exhaust velocity while handling the specified airflow volume.

3. Importance of Proper Flue Sizing

Details: Correct flue sizing ensures efficient removal of combustion gases, prevents backdrafting, maintains proper draft, and ensures furnace safety and compliance with building codes.

4. Using the Calculator

Tips: Enter CFM (cubic feet per minute) and velocity (feet per minute). Typical flue velocities range from 1,000 to 2,000 ft/min for residential applications. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: Why is flue sizing important for furnaces?
A: Proper flue sizing ensures safe removal of combustion gases, prevents carbon monoxide buildup, and maintains furnace efficiency.

Q2: What is the typical velocity range for furnace flues?
A: Residential furnace flues typically operate between 1,000-2,000 ft/min, while commercial systems may use higher velocities.

Q3: How do I determine the CFM for my furnace?
A: CFM can be calculated from furnace BTU rating or measured directly. Consult furnace specifications or a professional HVAC technician.

Q4: What happens if the flue is too small?
A: An undersized flue can cause poor draft, backdrafting, inefficient combustion, and potential safety hazards.

Q5: Are there building code requirements for flue sizing?
A: Yes, local building codes and manufacturer specifications must be followed. Always consult with a qualified professional for installation.