The number printed in kilowatts is not a quality score. It is a design choice that must match the building, climate and heating system.
The problem with choosing by floor area
Two homes with the same area can lose very different amounts of heat. Insulation, glazing, air leakage, exposure, room temperatures and ventilation all matter. Rules such as “one kilowatt per so many square metres” are useful only for an early estimate.
What happens when a unit is too small?
An undersized system may not maintain the required indoor temperature at the local winter design condition. It may rely more heavily on backup heat or run continuously. That does not mean continuous operation is automatically wrong—long, steady operation can be normal—but the design should explain how peak demand is met.
What happens when it is too large?
An oversized unit can cycle on and off frequently when demand is low. This may reduce comfort and efficiency and increase wear. The U.S. Department of Energy’s cold-climate sizing guidance warns that rules of thumb often lead to excessive oversizing.
Evidence to request
Ask for a room-by-room heat-loss calculation, the outdoor design temperature, intended flow temperature and manufacturer capacity data at those conditions. The proposal should also state assumptions about hot water, defrost and backup heat.
Compare the operating range
Do not compare only nominal output. Ask how far the compressor can modulate down during mild weather and how capacity changes in cold weather. Confirm that radiators or underfloor circuits can deliver the required heat at the proposed water temperature.
Before approving the order
Check that every supplier used the same building data. If two recommendations differ greatly, ask both designers to reconcile their heat-loss assumptions. The correct answer is a documented system design, not the largest machine within budget. Discuss your project with Thermovo.
Before requesting a project quotation
| Check | Information to prepare |
|---|---|
| Project scope | State the country, project type, operating conditions and required delivery date. Identify which decisions still need an installer or designer. |
| Topic-specific evidence | room heat-loss calculations and the model’s modulation range |
| Responsibility and acceptance | Record who supplies, installs, commissions and services the equipment. Ask which documents and checks are included, and confirm exclusions in writing. |
This checklist helps define a request; it is not a model performance claim, installation design or promise of availability.
Relevant equipment · Request a project quotation — Efficiency and sizing · About Thermovo
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