Internal Design Temperatures
Ctrl+D to bookmark this toolRecommended indoor temperature ranges for heating and cooling design from CIBSE Guide A. Quick reference for building services engineers.
Winter Heating Design Temperatures
CIBSE Guide A, Table 1.5 — Recommended indoor environmental conditions| Space Type | Operative Temp (°C) | Resultant Temp (°C) | Notes |
|---|---|---|---|
| Office (general) | 21–23 | 22 | Sedentary occupancy |
| Office (open plan) | 21–23 | 22 | — |
| Classroom | 19–21 | 20 | Active occupancy |
| Lecture theatre | 19–21 | 20 | — |
| Hospital ward | 22–24 | 23 | Patients resting |
| Operating theatre | 18–22 | 20 | Varies with surgical team preference |
| Consulting / exam room | 22–24 | 23 | — |
| Hotel bedroom | 19–21 | 20 | Guest comfort |
| Hotel lobby / reception | 19–21 | 20 | — |
| Retail (general) | 19–21 | 20 | Browsing / light activity |
| Retail (department store) | 19–21 | 20 | — |
| Restaurant / dining | 21–23 | 22 | Seated |
| Kitchen (commercial) | 16–18 | 17 | High internal gains |
| Sports hall | 13–16 | 14 | Active use |
| Swimming pool hall | 23–26 | 24 | 1°C above pool water temp |
| Car park (heated) | 5–10 | 7 | Frost protection only |
| Plant room | 10–16 | 12 | Equipment protection |
| Corridor / circulation | 19–21 | 20 | — |
| Toilet / WC | 19–21 | 20 | — |
| Warehouse | 12–16 | 14 | Depends on contents |
| Residential living room | 21–23 | 22 | BS EN 12831 |
| Residential bedroom | 17–19 | 18 | BS EN 12831 |
| Residential bathroom | 22–24 | 23 | — |
Operative temperature accounts for both air temperature and mean radiant temperature. In most well-insulated buildings, operative and air temperature are within 1°C.
Summer Cooling Design Temperatures
CIBSE Guide A, Table 1.5Summer design temperatures define the maximum acceptable indoor temperature during peak cooling conditions. These are NOT the setpoint — they are the upper limit used for plant sizing.
| Space Type | Max Summer Temp (°C) | Notes |
|---|---|---|
| Office (general) | 25–27 | TM52 overheating criteria also apply |
| Classroom | 25–28 | BB101 overheating criteria apply |
| Hospital ward | 25–28 | HTM 03-01 may set tighter limits |
| Retail | 25–27 | — |
| Hotel bedroom | 25–27 | — |
Summer design temperatures should be used alongside overheating assessments (CIBSE TM52 for non-domestic, TM59 for domestic). Meeting the design temperature alone does not guarantee compliance with Part O.
External Design Temperatures (UK)
CIBSE Guide A, Table 2.x — UK external design conditions| Location | Winter design (°C) | Summer design dry bulb (°C) | Notes |
|---|---|---|---|
| London (Heathrow) | -4.2 | 31.3 | Most commonly used |
| Birmingham | -5.2 | 29.4 | — |
| Manchester | -4.8 | 28.0 | — |
| Edinburgh | -5.9 | 26.3 | — |
| Belfast | -3.7 | 25.4 | — |
| Cardiff | -3.9 | 28.2 | — |
| Glasgow | -6.0 | 26.0 | — |
Winter design temperature is the 99.6% cold design condition. Summer design dry bulb is the 1% exceeded condition. Values from CIBSE Guide A. Use CIBSE weather files for dynamic simulation.
Key concept: The winter design temperature determines your heating load. The difference between internal design temp and external design temp (ΔT) drives heat loss calculations: Q = U × A × ΔT. For a London office: ΔT = 22 - (-4.2) = 26.2 K
MEP Desk uses these design temperatures in its calculation engine — enter room data and assumptions, and heat loss is calculated automatically.
Try MEP Desk free → See pricing →