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How to Calculate Heating Load

Heating Load Formula:

\[ Load = U \times A \times \Delta T + Infiltration \] \[ Infiltration = CFM \times 1.08 \times \Delta T \]

BTU/h-ft²-°F
ft²
°F
ft³/min

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1. What is Heating Load Calculation?

Heating load calculation determines the amount of heat energy required to maintain comfortable indoor temperatures during cold weather. It accounts for heat loss through building envelopes and air infiltration.

2. How Does the Calculator Work?

The calculator uses the heating load formula:

\[ Load = U \times A \times \Delta T + Infiltration \] \[ Infiltration = CFM \times 1.08 \times \Delta T \]

Where:

Explanation: The formula calculates heat loss through transmission (walls, windows, roof) plus heat loss due to air infiltration.

3. Importance of Heating Load Calculation

Details: Accurate heating load calculation is essential for proper HVAC system sizing, energy efficiency, occupant comfort, and preventing equipment oversizing or undersizing.

4. Using the Calculator

Tips: Enter U-coefficient based on construction materials, measure accurate surface areas, use design temperature differences, and estimate infiltration rates based on building tightness.

5. Frequently Asked Questions (FAQ)

Q1: What are typical U-values for different materials?
A: Single-pane windows: ~1.0, Double-pane: ~0.5, Well-insulated walls: ~0.05-0.1, Roofs: ~0.03-0.07 BTU/h-ft²-°F.

Q2: How do I estimate infiltration rates?
A: Tight construction: 0.1-0.3 ACH, Average: 0.3-0.5 ACH, Leaky: 0.5-1.0 ACH. Convert to CFM using room volume.

Q3: What design temperature difference should I use?
A: Use local 99% design temperature for outdoor and desired indoor temperature (typically 68-72°F).

Q4: Why is proper load calculation important?
A: Oversized systems short-cycle, reducing efficiency and comfort. Undersized systems cannot maintain temperature.

Q5: Should I include internal heat gains?
A: For heating load, internal gains (people, equipment) provide free heat and can reduce calculated load requirements.

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