Choose the quantity you need
For temperature rise, enter heat delivered to the air and airflow. For thermal power, enter airflow and the required temperature increase. For corresponding airflow, enter heat and a positive rise. The tool reports the same thermal balance in all three modes.
Use positive values for a heating case. Zero flow, zero rise, cooling and latent heating require a different interpretation and are not solved here. Numeric inputs clear when you change the target or airflow unit. Inputs and results stay in the page and are not saved or transmitted.
Method and worked examples
Neptronic's metric relationship is P = Q × ΔT × 1.21 / 3600, with heat P in kW, flow Q in m³/h, and ΔT = leaving minus entering air temperature in °C. Rearranging gives ΔT = P × 3600 / (Q × 1.21), or Q = P × 3600 / (ΔT × 1.21).
Example: 12.1 kW and 3600 m³/h (1000 L/s) give a 10°C rise. At the same flow, a 20°C rise corresponds to 24.2 kW. These are hypothetical arithmetic checks, not equipment settings or a recommended heater rating.
L/s is multiplied by 3.6 to obtain m³/h. CFM is multiplied by 1.69901079552, using the international foot of 0.3048 m. Every airflow unit is converted before applying the metric formula. The source's separately rounded imperial heat factors are not mixed into the calculation; small differences from that separate formula are possible.
The fixed 1.21 factor represents the catalogue's nominal air-property approximation. Its formula page does not establish a temperature, pressure or humidity correction model. Use a supported air-property method where those effects matter. Arithmetic retains precision; display uses three decimals or scientific notation.
Check the actual heater and air system
A thermal-balance airflow is not a manufacturer's minimum permitted flow or face velocity. Element construction, watt density, duct area, flow distribution, airflow proving, high-limit devices and control arrangements need the actual product instructions and qualified design review.
This model does not calculate fan pressure, pressure drop, duct leakage or heat loss. It does not infer an absolute leaving temperature without an entering temperature, or predict transient temperatures during a loss of flow. An enclosure's heat rise is also a different thermal problem.
For current from known electrical nameplate kW, use the AC electrical calculator. The thermal power calculated here does not establish electrical nameplate input, conductor ampacity or protection requirements.
Common questions
Is the calculated airflow the minimum safe flow?
No. It is the flow corresponding to the supplied heat and temperature rise in this approximate thermal equation. The equipment's permitted airflow and operating limits require its own instructions.
Is a 20°C rise a 20°C outlet temperature?
No. A rise is the difference between leaving and entering temperatures. This tool reports the difference; it does not assume an inlet temperature.
Does changing CFM to L/s change the heat model?
No. The tool uses exact volume/time unit conversions and the same metric catalogue equation in every unit mode.
Related tools
Source and scope
Neptronic, Electric Duct Heaters catalogue, printed page 43 / PDF page 45, “Formulas & Conversions,” footer identifier 170406; original checked November 10, 2026. The metric heat and temperature-difference relationships supply this method.
The catalogue equation is an approximate physical method, not a current Canadian code or equipment approval. Its adjacent electrical equations and product selection requirements are not applied here. Report a problem or suggest a source; inputs are not attached automatically.