Radiator Sizing
Calculate the perfect radiator size for your room using BTU calculations. Get accurate sizing recommendations for optimal heating efficiency.
Room Dimensions
Room Volume: 1059 ft³•Floor Area: 129 ft²
Insulation & Windows
Temperature & Orientation
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
Room Size
Calculate room volume (length × width × height)
Insulation
Consider wall insulation and window efficiency
BTU Calculation
Determine required heat output in BTUs or Watts
Radiator Selection
Choose radiator type and size based on calculations
How to Use the Radiator Calculator
How to Use the Radiator Calculator
- 1
Measure Room Dimensions
Calculate room volume: length × width × height in meters or feet. Radiator sizing based on volume, not just floor area. High ceilings require proportionally larger radiators.
- 2
Set Desired Temperature
Enter target room temp: Living areas 68-72°F (20-22°C), bedrooms 60-65°F (15-18°C), bathrooms 70-75°F (21-24°C). Higher targets require larger radiators and increase operating costs.
- 3
Determine Insulation Level
Assess room insulation: Poor (old windows, uninsulated walls), average (double-pane windows, basic wall insulation), good (modern windows, well-insulated). Poor insulation needs significantly larger radiators.
- 4
Check Flow Temperature
Identify your heating system water temp: Traditional boiler 160-180°F (70-82°C), condensing boiler 140-160°F (60-70°C), heat pump 95-110°F (35-43°C). Lower temps require larger radiators - crucial for heat pump systems.
- 5
Select Radiator Size
Calculator recommends radiator BTU/hr or Watt output needed. Match to manufacturer specs. Common sizes: 500W-3000W (1,700-10,200 BTU/hr). Oversizing is OK (provides backup capacity), undersizing causes cold rooms.
Pro Tip: Use Ctrl+Enter to calculate quickly, or Ctrl+R to reset the form.
Frequently Asked Questions
How do I know what size radiator I need?
Match radiator BTU output to room heat loss. Calculate room heat loss: volume × temperature difference × insulation factor. Typical: 50-100 BTU per sq ft. Check manufacturer specs for radiator output at your system's water temperature. Better insulated rooms need smaller radiators. Professional heat loss calculation recommended.
Can I use radiators with a heat pump?
Yes, but you need larger radiators. Heat pumps run at lower water temperatures (95-110°F) vs. traditional boilers (160-180°F). Lower temp = less output per radiator. Solution: install oversized radiators or fan-assisted radiators. Or install underfloor heating (works great with low-temp heat pumps).
Why is my radiator cold at the bottom/top?
Cold bottom: sludge buildup - flush system. Cold top: air trapped - bleed radiator. Cold one side: balancing issue - adjust lockshield valve. Cold entirely: valve stuck closed or pump failure. Regular bleeding (once/year) and system flushing (every 5 years) prevents most issues.
What's better - panel radiators or column radiators?
Panel radiators: more common, compact, better heat output per sq ft, cheaper ($100-400). Column radiators: traditional look, easier to clean behind, longer lifespan, higher cost ($300-1,200). Performance similar if sized correctly. Choose panel for efficiency/budget, column for aesthetics/traditional homes. Vertical radiators save wall space in small rooms.
How often should I bleed radiators?
Bleed radiators once/year at start of heating season, or whenever you hear gurgling or notice cold spots at top. Process: turn off heating, place container under bleed valve, turn key until air hisses out, close when water appears. Takes 5 minutes per radiator. Trapped air reduces efficiency 10-30% and causes noise. If needing frequent bleeding (monthly), check for system leaks or faulty pump.