Underfloor Heating vs. Radiators: Which System Suits Your Building?
The choice between underfloor heating and radiators is one of the most important decisions for new construction or renovation. Both systems have their merits – but which is optimal for your situation? In this article, we compare the technical basics, performance data and applications.
Technical Basics
Underfloor Heating According to DIN EN 1264
Underfloor heating is a surface heating system where heating pipes are laid in the screed. Heat transfer occurs primarily through radiation (approx. 60%) and convection (approx. 40%).
| Parameter | Value per DIN EN 1264 |
|---|---|
| Standard flow temperature | 35°C |
| Standard return temperature | 30°C |
| Standard room temperature | 20°C |
| Standard excess temperature | 12.5 K |
| Typical standard output | 75 W/m² (wet system) |
| Max. surface temperature (occupied area) | 29°C |
| Max. output occupied zone | ~100 W/m² |
| Max. output perimeter zone | ~175 W/m² |
Radiators According to DIN EN 442
Conventional radiators (panel, column, tubular) transfer heat through convection (70–80%) and radiation (20–30%).
| Parameter | Value per DIN EN 442 |
|---|---|
| Standard flow temperature | 75°C |
| Standard return temperature | 65°C |
| Standard room temperature | 20°C |
| Standard excess temperature | 50 K |
| Typical standard output | 2,650 W/m² (Type 22) |
| Radiator exponent | 1.30–1.35 |
Important difference: The standard outputs of both systems are measured under completely different conditions and are therefore not directly comparable. A Type 22 radiator with 2,650 W/m² standard output sounds much more powerful than underfloor heating with 75 W/m² – but these values apply at 75/65/20°C and 35/30/20°C respectively.
Comparing Performance Behaviour
The Temperature-Performance Diagram
The crucial question is: How much heat output does the system deliver at what flow temperature?
| Flow Temperature | Underfloor Heating | Type 22 Radiator |
|---|---|---|
| 35°C | 75 W/m² (100%) | ~140 W/m² (5%) |
| 40°C | 95 W/m² | ~230 W/m² (9%) |
| 45°C | 100 W/m² (Max) | ~350 W/m² (13%) |
| 50°C | 100 W/m² (Max) | ~500 W/m² (19%) |
| 55°C | 100 W/m² (Max) | ~690 W/m² (26%) |
| 65°C | – | ~1,100 W/m² (42%) |
| 75°C | – | 2,650 W/m² (100%) |
Why Does Underfloor Heating Behave This Way?
Underfloor heating has a physical ceiling:
- Maximum surface temperature: In the occupied area, the floor surface may reach a maximum of 29°C (comfort, health)
- Heat transfer through screed: Even at higher flow temperatures, heat output is limited by the restricted surface temperature
- Linear behaviour: In the permissible range, output rises almost linearly with excess temperature (exponent ≈ 1.0)
Physical maximum: Underfloor heating in the occupied area can deliver a maximum of about 100 W/m² – regardless of how high the flow temperature is. If the 29°C limit is exceeded, the floor becomes uncomfortably warm.
The Exponential Behaviour of Radiators
Radiators show strongly non-linear behaviour:
- Exponent n = 1.30–1.35: Output drops disproportionately at lower temperatures
- At 55/45°C (ΔT = 30K), a radiator delivers only about 26% of its standard output
- At 45/35°C (ΔT = 20K), only about 13% of standard output
Suitability for Heat Pumps
Seasonal Performance Factor and Flow Temperature
The efficiency of a heat pump (measured as seasonal performance factor SPF) depends strongly on the flow temperature:
| Flow Temperature | SPF (Air-Water HP) | Electricity Consumption |
|---|---|---|
| 35°C | 4.5–5.0 | Very low |
| 45°C | 3.5–4.0 | Low |
| 55°C | 2.8–3.2 | Medium |
| 65°C | 2.2–2.6 | High |
Underfloor Heating = Ideal Heat Pump Partner
| Advantage | Explanation |
|---|---|
| Low flow temperature | 35–40°C usually sufficient |
| High SPF | Electricity costs up to 40% lower |
| Large thermal mass | Buffer effect through screed |
| Slow response | Suits heat pump cycling |
| Even heat distribution | No convection currents |
Radiators with Heat Pump
Modern, generously sized radiators can also be operated with heat pumps:
| Requirement | Recommendation |
|---|---|
| Radiator type | Type 22 or better Type 33 |
| Sizing | 1.5–2× the calculated heating load |
| Flow temperature | Max. 55°C, preferably 45°C |
| Hydraulic balancing | Mandatory |
Rule of thumb: At 55°C flow temperature, a radiator must be about 4× as large as at 75°C to cover the same heating load!
Advantages and Disadvantages Overview
Underfloor Heating
| Advantages | Disadvantages |
|---|---|
| ✅ Low flow temperature (35–40°C) | ❌ Slow response (hours) |
| ✅ Ideal for heat pumps | ❌ High investment costs |
| ✅ Even heat distribution | ❌ Build-up height (5–10 cm) |
| ✅ No visible heating elements | ❌ Repairs complex |
| ✅ Free furniture placement | ❌ Not for all floor coverings |
| ✅ Hygienic (no dust circulation) | ❌ Limited output (~100 W/m²) |
| ✅ Pleasant radiant heat | ❌ Cooling function limited |
Conventional Radiators
| Advantages | Disadvantages |
|---|---|
| ✅ Fast response (minutes) | ❌ High flow temperature (55–75°C) |
| ✅ Lower investment costs | ❌ Less efficient with heat pump |
| ✅ Easy retrofit | ❌ Uneven heat distribution |
| ✅ High output density possible | ❌ Dust circulation (convection) |
| ✅ Easy repair/replacement | ❌ Restricted furniture placement |
| ✅ For all floor coverings | ❌ Visible heating elements |
| ✅ Flexibly sized | ❌ Radiator exponent reduces LT output |
Application Recommendations
New Build with Heat Pump
| Recommendation | Reason |
|---|---|
| Prefer underfloor heating | Maximum heat pump efficiency |
| Exception: Bathroom | Towel rail as addition useful |
| Exception: Rarely used rooms | Quick warm-up desired |
Renovation with Heat Pump
| Situation | Recommendation |
|---|---|
| Existing radiators large enough | Keep, hydraulically balance |
| Radiators undersized | Type upgrade (e.g. 11→33) |
| Screed renovation planned | Retrofit underfloor heating |
| Bathroom renovation | Underfloor heating + towel rail |
| Very high heating load (>100 W/m²) | Radiators or combination |
Hybrid Solutions
In many cases, a combination makes sense:
| Room | Recommendation |
|---|---|
| Living room | Underfloor heating (base load) |
| Kitchen | Underfloor heating |
| Bathroom | Underfloor heating + towel rail |
| Bedroom | Underfloor heating or small radiators |
| Office/study | Radiators (fast response) |
| Guest room | Radiators (rarely used) |
Calculation in the Heating Load Calculator
Entering Underfloor Heating Correctly
In our heating load calculator, you can record underfloor heating as a heat emitter:
| Parameter | Meaning |
|---|---|
| Type | Underfloor heating wet system/dry construction |
| Room length | Length of heated room |
| Room width | Width of heated room |
| Deduction area | Area under fitted furniture (not heated) |
Calculation logic: For underfloor heating, output is calculated according to DIN EN 1264 – linearly with excess temperature and limited to maximum 100 W/m² in the occupied area.
Performance Comparison at Different Temperatures
| System | At 35/30/20°C | At 45/35/20°C | At 55/45/20°C |
|---|---|---|---|
| UFH wet system (16 m²) | 1,200 W | 1,600 W (Max) | 1,600 W (Max) |
| Type 22 (1.6 m × 0.5 m) | 112 W | 275 W | 525 W |
| Type 33 (1.6 m × 0.5 m) | 154 W | 378 W | 722 W |
Optimisation Notes
For rooms with underfloor heating, our heating load calculator shows:
- ✅ No replacement recommendations – Surface heating is already optimal
- ✅ Maximum output info – Physical limits are considered
- ✅ Warning on overload – When heating load >100 W/m²
Economic Considerations
Investment Costs
| System | Cost per m² | For 120 m² Floor Area |
|---|---|---|
| Underfloor heating wet system | €50–80/m² | €6,000–9,600 |
| Underfloor heating dry construction | €70–120/m² | €8,400–14,400 |
| Radiators (Type 22) | €25–40/m² heating load | €3,000–4,800 |
| Radiators (Type 33) | €35–55/m² heating load | €4,200–6,600 |
Operating Costs with Heat Pump
| System | Flow Temperature | SPF | Annual Electricity Costs* |
|---|---|---|---|
| Underfloor heating | 35°C | 4.5 | ~€900 |
| Underfloor heating | 40°C | 4.0 | ~€1,000 |
| Radiators (optimised) | 45°C | 3.7 | ~€1,080 |
| Radiators (standard) | 55°C | 3.0 | ~€1,330 |
| Radiators (old stock) | 65°C | 2.4 | ~€1,670 |
*Assumption: 12,000 kWh heating demand, €0.30/kWh electricity price
Long-term savings: The higher investment costs of underfloor heating are recouped through lower operating costs. At €400–600 annual savings, payback is achieved after 10–15 years.
Conclusion
The Essentials: Underfloor heating is technically the ideal heat transfer system for heat pumps – it enables low flow temperatures and thus maximum efficiency. Its physical output limit of about 100 W/m² is sufficient for well-insulated new builds and energy-renovated old buildings. For unrenovated old buildings with high heat demand, large radiators or hybrid solutions are the better choice. Our heating load calculator automatically recognises surface heating and calculates output according to DIN EN 1264.
Try it now: Go to the Heating Load Calculator with Underfloor Heating Calculation
Further Reading
- Radiator Optimisation: Efficient Heating with Correct Sizing
- Understanding Heating Load Results
- U-Value Explained: Understanding Thermal Transmittance
Sources
- DIN EN 1264-1 to 1264-5: Room surface-integrated heating and cooling systems
- DIN EN 442: Radiators – Heat output
- DIN EN 12831-1: Heating load calculation
- VDI 6030: Designing room heating surfaces
- VDI 4645: Planning and dimensioning of heat pump systems