Pro Tool
Size Your Heating. To the BTU.
The UK property investor's heating calculator — BTU requirements, radiator sizing, heat loss analysis, and energy cost comparison for every room in your property.
Unlock BTU CalculatorRoom Analysis
A generic BTU table gives you one number for a room size. Propty considers 10+ factors — dimensions, ceiling height, insulation, glazing type, external walls, floor type, orientation, and room use. The result is a BTU figure you can actually rely on.
Cost Comparison
The cheapest radiator means nothing if the running costs are high. Propty compares the annual heating cost for each room across different fuel types — so you can make an informed decision about your heating system, not just your radiator size.
BTU (British Thermal Unit) measures heat energy. One BTU is the energy needed to raise 1 pound of water by 1 degree Fahrenheit. In property terms, the BTU rating tells you how powerful a radiator or heater needs to be to warm a room to a comfortable temperature. Undersizing means a cold room; oversizing wastes energy and money.
The basic formula starts with room volume (length x width x height) and multiplies by a factor based on insulation and glazing quality. However, other factors matter too — number of external walls, floor type, room orientation, and room use. Our calculator handles all of these automatically.
A typical UK bedroom (3m x 4m, 2.4m ceiling, double glazed, one external wall) needs approximately 3,500-4,500 BTU. Larger bedrooms, poor insulation, or multiple external walls increase this. Our calculator gives you the exact figure for your specific room.
Significantly. Double glazing roughly halves the heat loss through windows compared to single glazing. For a room with a large window, upgrading from single to double glazing can reduce the BTU requirement by 15-25%, saving on both radiator size and running costs.
It depends on the room's BTU requirement, how many hours you heat it, and your fuel type. A typical living room (6,000 BTU) heated 8 hours/day on gas costs roughly £180-£250/year at 2025 tariffs. Electric heating costs 3-4x more per unit. Our tool calculates the exact figure for your rooms.