1. What is a Heat Calculator (UK Standards)?

Definition: This calculator estimates heat loss in watts according to UK standards (BS EN 12831) for building thermal performance.

Purpose: It helps architects, engineers, and builders determine heating requirements for rooms and buildings.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( Q \) — Total heat loss (Watts)
• \( U \) — U-value of the surface (W/m² K)
• \( A \) — Surface area (m²)
• \( \Delta T \) — Temperature difference (Kelvin)
• \( V \) — Room volume (m³)
• \( ACH \) — Air changes per hour (1/h)

Explanation: The formula calculates both conductive heat loss through surfaces and ventilation heat loss through air changes.

3. Importance of Heat Loss Calculation

Details: Accurate heat loss calculations ensure proper heating system sizing, energy efficiency, and compliance with UK building regulations.

4. Using the Calculator

Tips: Enter the U-value, surface area, temperature difference, room volume, and air changes per hour (default 0.5). All values must be ≥ 0.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical U-value for UK buildings?
A: For external walls, current Building Regulations require U-values of 0.18-0.30 W/m²K depending on the element.

Q2: How do I determine the temperature difference (ΔT)?
A: ΔT is the difference between desired indoor temperature and design external temperature (typically 21°C - (-3°C) = 24K in the UK).

Q3: What are typical ACH values?
A: 0.5 for modern airtight homes, 1.0 for average homes, 1.5-2.0 for leaky older buildings.

Q4: Why is the factor 0.33 used?
A: It's the product of air's specific heat capacity (0.33 Wh/m³K) converting hourly air changes to heat loss.

Q5: Does this include thermal bridging?
A: No, for precise calculations you should add an additional 10-20% for thermal bridges or use specialist software.