Heat Loss Calculator

Type of room: Living Room Bedroom Hallway or Kitchen Bathroom Width of room (m): What is below the room? Heated room Soil under wooden floor Soil under solid concrete floor Air under suspended concrete floor Length of room (m): What is above the room? Heated room A pitched uninsulated roof Pitched roof insulated 50mm Pitched roof insulated 100mm Flat roof uninsulated Flat roof insulated Window Area (m²): Type of outside walls: Brick Cavity Insulated Brick Cavity 105mm Solid Brick 220mm Solid Brick Wood frame Height of room (m): Type of windows: Wood/Plastic double glazed Metal double glazed Metal Single glazed Wood Single glazed Number of outside walls: One Two Three Heat loss in Watts: Heat loss in BTU's:

 

Think of the heat loss calculator as a “heater size guesser” that actually does the maths for you instead of guessing.

Why it’s important (in simple terms) If your heater is too small, the room never really gets warm. You keep it on full blast, you’re cold, and you waste money. If your heater is too big, you paid extra for power you don’t need, and you may run it inefficiently.

The calculator uses the room size and how “leaky” it is (windows, walls, floor, ceiling, what’s above/below) to estimate how much heat the room loses.

Once you know the heat loss in Watts/BTUs, you can pick a heater that actually matches what the room needs. When it’s useful Choosing new heaters or radiators: “What size heater do I need in this bedroom/living room?” Replacing old storage heaters: “My old one was X kW; is that correct or should I go bigger/smaller?” Renovations/insulation changes: you add double glazing or loft insulation and want to see how much less heat you need.

Comparing rooms in a house: some rooms always feel cold; the calculator shows which ones lose the most heat, so you can prioritise. In plain language: it stops you guessing, so you don’t end up cold or wasting money on the wrong heater.