Heating power calculator
Heater or radiator power from room volume and a specific heat requirement.
Fill in the fields and the result will appear here automatically.
Show a simple volume-based estimate with ceiling height as a separate input. At the same floor area,2.7→3.2 m raises the volume term by about 18.5%; changing the selected coefficient 30→50 W/m³ raises it by 66.7%. The fixed 100 W per window is a formula assumption. These figures compare scenarios; they do not replace envelope and ventilation heat-loss calculations or equipment sizing.
How it works
Formula and logic
Preserved volume-based estimate: V=A×H m³ and W=V×q+100×N watts, with entered q W/m³ and nonnegative whole window count N. Kilowatts=W/1000. The 100 W addition is this model’s fixed assumption, not a measured loss for every window. Envelope transmission, outdoor temperature, infiltration and heater performance are not calculated.
Example
A 20 m² room with a 2.7 m ceiling and one window at 40 W/m³ needs 2.26 kW. The same room without windows gives 2.16 kW; with one window 2.26 kW is retained without automatic rounding up.
Fields and units
- Floor area, m² — m²
- Ceiling height, m — m
- Specific requirement, W/m³ — W/m³
- Number of windows — unitless
How to use
- — Enter the floor area and the ceiling height — the calculation works from volume.
- — Enter your chosen W/m³ coefficient;30,40 and 50 are comparison assumptions, not standard insulation classes.
- — Enter the number of windows — each adds a hundred watts.
- — Compare scenarios in kW; equipment sizing needs a separate heat-loss calculation.
Method and limitations
- Calculation method
- Formula and logic
- Data or methodology source
- DOE/PNNL: design heating load needs calculation; not validation of W/m³ or 100 W per window
- Limitation
- The 100 W addition is this model’s fixed assumption, not a measured loss for every window. Envelope transmission, outdoor temperature, infiltration and heater performance are not calculated.
FAQ
Why work from volume rather than floor area?
That is how this estimate is defined: height scales the volume term. At 2.7→3.2 m it rises 18.5%, but the total with a fixed window addition rises less. Actual heating load depends on heat loss, not only the quantity of air.
Which specific requirement should I choose?
Choose a value for your estimate in W/m³.30,40 and 50 may be compared as scenarios; they are not verified building classes or local climate requirements here. Equipment selection needs a design heat-loss calculation.
Where does the hundred watts per window come from?
From the preserved model assumption: exactly 100 W per entered window. Size, glazing, temperature and air leakage are absent, so this is neither measured heat loss nor a universal engineering standard.
Does this apply to underfloor heating?
Only the estimated heat load can be compared. The calculation does not determine allowed floor output, surface temperatures, circuits or pipe spacing. Check the actual system against design load separately.
Should I allow spare capacity?
The calculator prescribes no spare capacity. Its need depends on design load and equipment characteristics; oversizing may also impair operation. An arbitrary 10–20% is not treated as a rule here.