EngineerHub.orgRoom size
Measure the room; the calculator works out floor area and volume.
How easily the room gains heat
Choose the closest description; no engineering coefficient is required.
Advanced: enter a known room heat-loss coefficient
Sunny windows
Enter only glass that receives meaningful direct sun.
Hot-day weather
Choose a preset. Open advanced settings only when you know local conditions.
People, appliances and current ventilation
Choose the closest daily pattern rather than guessing watts.
Build a combined solution
Choose one sun-control option, then add any compatible ventilation, heat-reduction or cooling measures.
A. Block solar heat
B. Ventilate intelligently
C. Reduce or remove heat
24-hour room-temperature comparison
Worked example: west-facing apartment
- A 5 m × 5 m room has 6 m² of west-facing glass and no daytime shading.
- A hot day is selected: 20°C overnight and 32°C in the afternoon.
- The current case uses ordinary background ventilation and normal internal heat from occupants and devices.
- The user then combines external shading, smart daytime windows and strong night ventilation.
- The chart compares the current room with the selected plan after several repeated warm days, so the result is not dominated by one arbitrary starting temperature.
Background and recommendations
The page hides unnecessary engineering inputs but keeps the model transparent.
The model adds solar heat through glass, heat from people and appliances, and heat exchange through the building fabric and ventilation. In beginner mode, the room heat-loss coefficient is estimated from floor area, room exposure and insulation quality.
The room is simulated through repeated identical hot days before the final 24-hour chart is shown. This reduces sensitivity to the arbitrary starting temperature and captures heat stored in walls and furniture.
Public hot-weather guidance commonly recommends shading sun-facing windows, reducing unnecessary internal heat, and opening windows when outdoor air is cooler—often at night—where it is safe to do so.
It is a useful comparison point used in several overheating and heat-health contexts, but it is not a universal safe/unsafe boundary. Vulnerable occupants may need cooler conditions and overnight recovery is important.
This is a one-zone lumped-capacitance screen. It does not calculate humidity, exact sun position, neighbouring rooms, wind pressure, detailed thermal bridges or regulatory compliance. Use measurements and professional dynamic simulation for important design decisions.
Frequently asked questions
No. It is an adjustable comfort and screening reference. Heat risk depends on humidity, duration, night-time recovery, health, age, medication, activity and access to cooling.
External shading intercepts much of the solar energy before it passes through the glazing. Internal blinds act after some solar energy has already entered the window system.
No. Opening windows can heat the room when outdoor air is hotter. Ventilation is most useful when outside air is cooler than the room, often during evening, night and early morning.
It provides a preliminary sensible cooling estimate only. Final equipment selection requires climate design data, latent loads, adjacent zones, infiltration, duct losses, equipment performance and local practice.