How to Do a Heat Loss Calculation on a House

Heat Loss Equation:

\[ Q = U \times A \times \Delta T + \text{Infiltration} \]

U-Value (U):

BTU/h-ft²-°F

Area (A):

ft²

Temperature Difference (ΔT):

°F

Infiltration:

CFM

Total Heat Loss (Q):

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1. What Is Heat Loss Calculation?

Heat loss calculation is a method used to determine the amount of heat energy that escapes from a building through its envelope and air infiltration. This calculation helps in properly sizing heating systems and improving energy efficiency.

2. How Does the Calculator Work?

The calculator uses the heat loss equation:

\[ Q = U \times A \times \Delta T + \text{Infiltration} \]

Where:

\( Q \) — Total heat loss (BTU/h)
\( U \) — U-value or thermal transmittance (BTU/h-ft²-°F)
\( A \) — Surface area (ft²)
\( \Delta T \) — Temperature difference between inside and outside (°F)
\( \text{Infiltration} \) — Air leakage heat loss (CFM converted to BTU/h)

Explanation: The equation calculates heat loss through building envelope (walls, windows, roof) plus additional losses from air infiltration and ventilation.

3. Importance of Heat Loss Calculation

Details: Accurate heat loss calculation is essential for proper HVAC system sizing, energy efficiency improvements, building code compliance, and reducing energy costs while maintaining comfort.

4. Using the Calculator

Tips: Enter U-value in BTU/h-ft²-°F, area in square feet, temperature difference in °F, and infiltration in CFM. All values must be positive numbers for accurate calculation.

5. Frequently Asked Questions (FAQ)

Q1: What is U-value and how do I find it?
A: U-value measures how well a building element conducts heat. Lower values indicate better insulation. You can find U-values in building material specifications or use standard values for common constructions.

Q2: How do I calculate infiltration?
A: Infiltration can be estimated using blower door tests, air change rates, or calculated based on building tightness and volume. Professional energy audits provide the most accurate measurements.

Q3: What temperature difference should I use?
A: Use the design temperature difference for your location - typically the difference between desired indoor temperature (e.g., 68°F) and the outdoor design temperature for your climate zone.

Q4: Why is accurate heat loss calculation important?
A: Oversized heating systems cycle frequently reducing efficiency and comfort, while undersized systems cannot maintain desired temperatures during extreme weather conditions.

Q5: Can this calculator be used for commercial buildings?
A: While the principles are the same, commercial buildings often require more detailed calculations accounting for internal heat gains, ventilation requirements, and complex building geometries.