Radiator Sizing

Calculate the perfect radiator size for your room using BTU calculations. Get accurate sizing recommendations for optimal heating efficiency.

Room Dimensions

4m
1m50m
3m
1m50m
2.5m
2m10m

Room Volume: 30.00 m³•Floor Area: 12.00 m²

Insulation & Windows

2
1234
1
0510

Temperature & Orientation

20°C
16°C25°C
-5°C
-30°C10°C
25°C

Energy Cost & Comparison

Radiator Types & Efficiency

Understanding different radiator types and their heating characteristics

Single Panel

Basic radiators for smaller rooms, lower heat output

Double Panel

Higher heat output, ideal for most residential rooms

Designer

Stylish options with variable heat output capabilities

Radiator Sizing Guide

Key factors to consider when choosing the right radiator size

1

Room Size

Calculate room volume (length × width × height)

2

Insulation

Consider wall insulation and window efficiency

3

BTU Calculation

Determine required heat output in BTUs or Watts

4

Radiator Selection

Choose radiator type and size based on calculations

  1. 1

    Measure Room Dimensions

    Calculate room volume: length × width × height in metres. Radiator sizing based on volume, not just floor area. High ceilings require proportionally larger radiators. Standard UK rooms: 2.4m ceiling height.

  2. 2

    Set Desired Temperature

    Enter target room temperature: Living areas 19-21°C, bedrooms 16-18°C, bathrooms 22-24°C. Higher targets require larger radiators and increase operating costs. UK building regulations assume 21°C for living areas.

  3. 3

    Determine Insulation Level

    Assess room insulation: Poor (single glazing, solid walls, no loft insulation), average (double glazing, cavity walls, basic loft insulation), good (A-rated windows, insulated walls, 270mm+ loft). Poor insulation needs significantly larger radiators - sometimes 50-100% bigger output.

  4. 4

    Check Flow Temperature

    Identify your heating system water temperature: Traditional boiler 70-82°C, condensing boiler 60-70°C, heat pump 35-50°C. Lower temperatures require larger radiators - crucial for heat pump systems. Heat pumps often need double the radiator size vs traditional boilers for same heat output.

  5. 5

    Select Radiator Size

    Calculator recommends radiator output needed in Watts or BTU/hr. Match to manufacturer specifications at your flow temperature. Common UK sizes: 500W-3000W. Type 21 (double panel, single convector) and Type 22 (double panel, double convector) most common. Oversising acceptable (provides backup capacity), undersising causes cold rooms. Allow 10-15% margin.

Pro Tip: Use Ctrl+Enter to calculate quickly, or Ctrl+R to reset the form.

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