Editorial correction: This guide uses manufacturer documentation. ThermalFinn has not performed firsthand heater testing. Unsupported measurements, rankings and universal installation prescriptions from earlier versions have been removed.

Measure the Interior

Record the finished interior length, width and height. For a rectangular room, multiply these dimensions using the same unit throughout. A room measuring 2 × 2 × 2.2 metres has a geometric volume of 8.8 m³. Use our room-volume tool for that calculation.

Volume alone does not select a heater. Record glass doors and windows, exposed masonry, insulation and the planned bench and heater positions. An irregular room needs an appropriate measurement of each part.

Use the Exact Regional Manual

Compare the room with the sizing instructions for the specific item number and electrical version. Apply only the adjustments the manufacturer specifies. The former universal correction factors and promised heat-up times on this page have been withdrawn.

For example, Harvia lists a 141–494 ft³ room range for the North American PC90E item HPCS9U1HUL. That published range is a starting point for reviewing that model’s instructions; it is not a recommendation for every room within those dimensions. HUUM publishes different room ranges for the DROP power variants and offers regional voltage selections.

Check the Installation Together

Give your retailer or installer the room dimensions, construction details and exact model documentation. Have them review clearances, ventilation, controller and sensor positions, and electrical compatibility before ordering. Do not choose breaker or cable sizes from room volume.

A larger heater is not automatically an acceptable substitute. The selected model must fit the manufacturer’s room and installation requirements. Request confirmation when the room is close to a published limit or has substantial glass or exposed masonry.

Continue Your Comparison

Manufacturer Sources

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