One of the most common questions we receive is: How many sections do I need for my room? Sizing your cast iron radiator correctly is essential to ensure comfort without over- or under-heating your space.
The size of a radiator is determined by the amount of heat required to warm your room—measured in BTUs (British Thermal Units). Factors that affect this include room dimensions, number of windows, insulation quality, and whether the room is north-facing.
To get a quick estimate:
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Measure your room (length x width x height)
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Multiply the volume by 4 or 5 for a well-insulated home; by 6 or 7 for older or draughty homes
This gives you a rough BTU requirement. Once you have your figure, consult a radiator BTU chart to find how many sections of your preferred cast iron radiator are needed. For example, if each section emits 450 BTUs, and you need 5,400 BTUs, you’d need a 12-section radiator.
Professional installers or suppliers can offer more tailored guidance using software that accounts for architectural features and heating systems. And remember—when in doubt, it's usually better to slightly overspec and fit thermostatic valves to regulate.
