Calculator Inputs
Engineering Heating AnalysisExample Data Table
| Case | Rated Output (W) | Reference Temps (°C) | Actual Temps (°C) | Exponent n | Install Factor | Corrected Output (W) |
|---|---|---|---|---|---|---|
| Panel Radiator A | 1800 | 75 / 65 / 20 | 60 / 50 / 21 | 1.30 | 1.00 | 1167.70 |
| Low Temperature Loop | 1500 | 70 / 55 / 20 | 50 / 40 / 21 | 1.28 | 0.95 | 730.68 |
| Covered Radiator | 2200 | 80 / 60 / 20 | 65 / 55 / 22 | 1.33 | 0.88 | 1244.79 |
Formula Used
Corrected radiator output:
Qactual = Qreference × (ΔTactual / ΔTreference)n × Finstall
Mean water temperature:
Tmean = (Tsupply + Treturn) / 2
Temperature difference to the room:
ΔT = Tmean − Troom
Required water flow rate:
Flow (L/h) = Qactual × 3600 / (4186 × (Tsupply − Treturn))
This method is widely used for converting catalog radiator ratings to real operating conditions. The exponent accounts for nonlinear radiator behavior as temperature differences change.
How to Use This Calculator
- Enter the radiator rated output from a catalog or test sheet.
- Fill in the reference supply, return, and room temperatures for that rating.
- Enter actual operating supply, return, and room temperatures for your system.
- Use the radiator exponent from manufacturer data or keep the typical default.
- Apply an installation correction factor for covers, recesses, or assisted airflow.
- Optionally add radiator size and target room heat load for deeper checks.
- Press the calculate button to show results above the form.
- Download the result as CSV or PDF for records and design notes.
Frequently Asked Questions
1. What does radiator heat output mean?
It is the useful heating power a radiator can deliver under specific operating temperatures. The value is usually expressed in watts and can also be shown in BTU per hour.
2. Why is corrected output lower than rated output?
Catalog ratings often use hotter water and fixed room temperatures. When your real system runs at lower temperatures, the temperature difference falls and the radiator emits less heat.
3. What is the radiator exponent?
The exponent describes how radiator output changes as temperature difference changes. Many panel radiators use a value near 1.3, but manufacturer data is always better.
4. Why use mean water temperature?
Water cools as it travels through the radiator. Averaging supply and return temperatures gives a practical emitter temperature for estimating the driving difference against room air.
5. What does the installation factor represent?
It adjusts performance for site conditions. Covers, deep shelves, and recesses may reduce output, while forced airflow or favorable mounting may improve delivered heat.
6. Can I compare the result to room heat load?
Yes. Enter the target room heat load to see coverage percentage and surplus or deficit. This helps you judge whether one radiator can satisfy the design requirement.
7. Why is flow rate included?
Flow rate shows the water volume needed to carry the calculated heat output at the chosen supply and return temperatures. It is useful for balancing and circuit checks.
8. Is this calculator useful for low temperature heating?
Yes. It is especially useful for heat pumps and condensing systems because real emitter output changes strongly when water temperatures drop below traditional radiator ratings.