Internal Heat Gains Reference
Ctrl+D to bookmark this toolOccupant, lighting, and equipment heat gains for cooling load calculations. Data from CIBSE Guide A, Section 6.
Occupant Heat Gains
CIBSE Guide A, Table 6.3Occupant heat gains have sensible and latent components. The split depends on the activity level. Higher activity produces more latent (moisture) gain and less sensible gain as a proportion of the total.
| Activity | Total (W) | Sensible (W) | Latent (W) | Typical Application |
|---|---|---|---|---|
| Seated quietly | 115 | 70 | 45 | Cinema, theatre |
| Light office work | 130 | 75 | 55 | General office |
| Standing / light work | 150 | 75 | 75 | Retail, reception |
| Walking (slow) | 160 | 80 | 80 | Corridors, circulation |
| Light bench work | 235 | 105 | 130 | Workshop, lab |
| Heavy work | 440 | 185 | 255 | Gym, factory |
| Dancing | 265 | 105 | 160 | Dance studio, club |
Values are per person at approximately 21°C room temperature. Sensible gains increase and latent gains decrease as room temperature falls below 21°C. For exact split at different temperatures, refer to CIBSE Guide A Table 6.3 footnotes.
Equipment Heat Gains
CIBSE Guide A, Table 6.5 and industry practice| Equipment / Space Type | Typical Gain | Basis | Notes |
|---|---|---|---|
| General office | 15–25 W/m² | Floor area | Includes PCs, monitors, printers |
| Trading floor / intensive IT | 30–50 W/m² | Floor area | Dense monitor/PC usage |
| Desktop PC (modern) | 65–100 W | Per unit | Varies with load |
| Laptop | 30–50 W | Per unit | Lower than desktop |
| Monitor (LCD) | 25–40 W | Per unit | Size dependent |
| Laser printer (small) | 50–200 W | Per unit | Peaks during printing |
| Photocopier | 200–400 W | Per unit | Peaks during use |
| Projector | 200–400 W | Per unit | — |
| Kitchen (commercial) | 30–80 W/m² | Floor area | Highly variable |
| Server room | 500–2000 W/m² | Floor area | Based on rack density |
Equipment gains shown are heat emission to the space, not electrical consumption. For IT equipment, the nameplate rating is typically higher than actual heat output. Use diversity factors where appropriate — not every device runs at peak simultaneously.
Lighting Heat Gains
CIBSE Guide A, Table 6.4; Part L benchmarks| Space Type | Typical LPD (W/m²) | Notes |
|---|---|---|
| Office (LED) | 8–12 | Modern LED lighting |
| Office (fluorescent legacy) | 12–18 | Older T5/T8 installations |
| Retail (general) | 15–25 | Display lighting adds significant load |
| Classroom | 8–12 | — |
| Hospital (ward) | 8–10 | — |
| Hospital (corridor) | 5–8 | Emergency lighting additional |
| Warehouse | 5–10 | High bay LED |
| Car park | 3–5 | — |
All lighting power is converted to heat. In a cooling calculation, lighting W/m² equals lighting heat gain W/m². Part L (2021) sets maximum allowable lighting energy for new buildings — typical modern LED installations are well within these limits.
LPD = Lighting Power Density. Values are installed power, not illuminance. For illuminance targets (lux), refer to CIBSE SLL Code or BS EN 12464-1.
Solar Gains (Brief Note)
Solar gains through glazing are often the dominant cooling load in UK commercial buildings. Solar gain calculation is complex and depends on orientation, glass type, shading, and time of day. CIBSE Guide A Section 5 and the CIBSE solar irradiance tables provide the methodology. For early-stage estimates, a cooling allowance of 40–100 W/m² of glazed area (peak, unshaded, south-facing) is commonly used, but always verify with proper calculation.
MEP Desk includes sensible heat, cooling load, and heat gain calculators — with room-level context and project assumptions built in.
Try MEP Desk free → See pricing →