HVAC Heating Load Calculation Manual

Basic Heating Load Formula:

\[ BTU/h = U \times A \times \Delta T + \text{Infiltration} + \text{Ventilation} \]

U-value (U):

BTU/h-ft²-°F

Area (A):

ft²

Temperature Difference (ΔT):

°F

Infiltration Loss:

BTU/h

Ventilation Loss:

BTU/h

Total Heating Load:

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1. What is HVAC Heating Load Calculation?

The HVAC 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 envelope, infiltration, and ventilation requirements.

2. How Does the Calculator Work?

The calculator uses the basic heating load formula:

\[ BTU/h = U \times A \times \Delta T + \text{Infiltration} + \text{Ventilation} \]

Where:

\( U \) — U-value (thermal transmittance) of the building component
\( A \) — Area of the building component
\( \Delta T \) — Temperature difference between inside and outside
\( \text{Infiltration} \) — Heat loss from air leakage
\( \text{Ventilation} \) — Heat loss from required fresh air intake

Explanation: The formula calculates conductive heat loss through surfaces plus additional losses from air exchange.

3. Importance of Accurate Heating Load Calculation

Details: Proper sizing of heating equipment is crucial for energy efficiency, comfort, and equipment longevity. Oversized systems short-cycle, while undersized systems can't maintain temperature.

4. Using the Calculator

Tips: For complete calculations, perform this for all building components (walls, windows, roof, etc.) and sum the results. Include all heat loss pathways for accurate sizing.

5. Frequently Asked Questions (FAQ)

Q1: What's a typical U-value for residential walls?
A: Modern insulated walls typically have U-values between 0.05-0.10 BTU/h-ft²-°F. Older homes may be 0.25 or higher.

Q2: How do I estimate infiltration losses?
A: Use the formula: Infiltration = 0.018 × Volume × ΔT × ACH (air changes per hour). Typical ACH is 0.5-1.5 for tight to average homes.

Q3: What temperature difference should I use?
A: Use the design temperature difference (indoor temp minus outdoor design temp for your location).

Q4: Should I include internal heat gains?
A: For heating load calculations, internal gains (people, appliances) are typically not subtracted as they're unreliable during coldest conditions.

Q5: Is this calculator suitable for whole-house calculations?
A: This provides a component calculation. Whole-house calculations require summing all components and may need professional software for complex buildings.