# Heating Load Calculator

Load, radiator sections, fuel use and running cost.

- Page: https://jianzhujisuan.com/en/heating-load
- Category: M&E (https://jianzhujisuan.com/en/c/me)
- Chinese version: https://jianzhujisuan.com/zh/heating-load.md
- Data checked: 2026-10-25

## Quick result

With the default inputs (Floor area 100 m², Storey height 3 m, Heat index 60 W/m², Indoor design 18 °C, Outdoor design -5 °C, Heating days 120 days, Gas price 2.8 CNY/m³): **Heating load 6.00 kW**

## Inputs

| Parameter | Type | Default | Unit | Note |
|---|---|---|---|---|
| Floor area | number | 100 | m² |  |
| Storey height | number | 3 | m |  |
| Heat index | number | 60 | W/m² | Efficient housing 40-60, ordinary 60-80, public 80-120 |
| Indoor design | number | 18 | °C |  |
| Outdoor design | number | -5 | °C |  |
| Heating days | number | 120 | days |  |
| Gas price | number | 2.8 | CNY/m³ |  |

## Formula

- **Load**: area × heat index in watts
- **Volume check**: volume × 0.55 × ΔT
- **Radiator sections**: load ÷ output per section
- **Gas rate**: Q × 3.6 ÷ (35.6 × efficiency)
- **Season use**: hourly rate × hours/day × days
- **Units**: 1 kW = 860 kcal/h = 3412 BTU/h

## Worked example

100 m² at 60 W/m², 18°C indoors against −5°C outside over 120 days at 2.8 per m³: 6.00 kW (volume method 3.79 kW), 50 radiator sections, 0.67 m³/h of gas, 971 m³ for the season and about 2718 in cost.

## Questions

### Why does the index vary twofold?

Because insulation levels differ. U-values fall from 1.8 W/(m²·K) for old 240 mm brickwork to 0.4 with external insulation and double glazing — a fourfold gap. Windows are the weak point, losing 40-50% of a house's heat with single glazing, which is why replacing windows usually beats thickening walls.

### What indoor temperature is right?

18-20°C is the comfort band for dwellings. Each degree adds 6-8% to energy, so lifting a 100 m² home from 18 to 22 costs an extra 600-800 over a season. Below 16 it is uncomfortable; above 24 the air is dry, occupants get headaches and consumption jumps. Hospitals and public buildings follow their own standards, with theatres at 22-25°C.

### Radiators or underfloor heating?

Underfloor runs at 35-45°C supply, feels better with warm feet and cool head, frees the wall, but heats up slowly over 4-6 hours, raises the floor 60-80 mm and is hard to repair. Radiators run at 70-85°C, warm a room in 20 minutes and are easy to service, but take wall space and stir dust. Tight floor-to-ceiling or intermittent use favours radiators; continuous occupation favours underfloor.

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Generated by BuildCalc. All calculations run in your browser; no data is uploaded. Formulas follow national standards and common trade practice; local codes govern.