Combustion Air Calculator HVAC

Combustion Air Formula:

\[ CFM = \frac{Total\ BTU}{100} \]

CFM (ft³/min):

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1. What is Combustion Air Calculation?

Combustion air calculation determines the amount of fresh air required for proper combustion in HVAC appliances. Adequate combustion air is essential for efficient operation and safety of fuel-burning equipment.

2. How Does the Calculator Work?

The calculator uses the combustion air formula:

\[ CFM = \frac{Total\ BTU}{100} \]

Where:

\( CFM \) — Cubic Feet per Minute of combustion air
\( Total\ BTU \) — Total British Thermal Units per hour of all combustion appliances

Explanation: This formula provides the minimum required combustion air flow rate based on the total BTU input of all fuel-burning appliances in the space.

3. Importance of Combustion Air Calculation

Details: Proper combustion air supply ensures complete combustion, prevents backdrafting, maintains appliance efficiency, and eliminates safety hazards like carbon monoxide production.

4. Using the Calculator

Tips: Enter the total BTU rating of all combustion appliances in the space. This includes furnaces, water heaters, boilers, and any other fuel-burning equipment.

5. Frequently Asked Questions (FAQ)

Q1: Why is 100 used as the divisor in the formula?
A: The factor of 100 represents the approximate amount of air (in CFM) needed per 100 BTU/h of appliance input, based on standard combustion requirements.

Q2: What happens with insufficient combustion air?
A: Inadequate combustion air can cause incomplete combustion, reduced efficiency, flame rollout, carbon monoxide production, and potential appliance damage.

Q3: Are there different calculation methods?
A: Yes, some codes may use different factors or more complex calculations based on room volume, appliance type, and installation conditions.

Q4: When is combustion air required?
A: Combustion air provisions are needed when appliances are in confined spaces or when natural infiltration is insufficient for combustion needs.

Q5: What about high-efficiency appliances?
A: Direct-vent or sealed combustion appliances may have different air requirements as they draw combustion air from outside.