Heat Pump Calculator (SPF Calculation)
Calculate the seasonal performance factor of your heat pump according to VDI 4650 – free and standard-compliant.
Quick Start
What does this calculator compute?
The heat pump calculator determines the Seasonal Performance Factor (SPF) of your heat pump according to VDI 4650. The SPF is the most important efficiency metric and indicates how much heat the heat pump generates on average from one unit of electricity over a year.
Simply explained: An SPF of 4.0 means: From 1 kWh of electricity, 4 kWh of heat are produced – 3 kWh come from the environment (free!), only 1 kWh from the electricity.
What you get from the calculator:
- Seasonal Performance Factor (SPF/SCOP): The central efficiency metric according to VDI 4650
- Electricity consumption: Annual electricity demand for heating and hot water [kWh/a]
- Operating costs: Annual electricity costs based on your tariff [€/a]
- Monthly breakdown: Heat demand and COP for each month
- CO₂ balance: Environmental impact of your heat pump
Important: The SPF should not be confused with the COP! The COP is a laboratory value under fixed conditions, the SPF is the realistic annual average. The SPF is therefore always slightly lower than the best COP.
3 Steps to Your Result
Step 1: Capture Heat Demand
Enter the heat demand of your building:
Option A: Import from heating load calculator (recommended)
- Have you already performed a heating load calculation?
- Simply enter the 5-digit project key
- Design heating load, location and system temperatures are automatically imported
Option B: Manual entry
- Design heating load [kW]: The maximum heating capacity at design temperature
- Unknown? Guideline: 40-60 W/m² for unrenovated old buildings, 20-40 W/m² for renovated buildings
- Postal code: For automatic climate data (design outdoor temperature)
Hot water demand (DHW):
- Enter the annual hot water demand [kWh/a]
- Or use the Hot water assistant (calculator icon):
- Number of people in household
- Shower behavior (economical/normal/extensive)
- Bathtub usage
- NEW: Heating strategy – Choose when water is heated (midday = more efficient!)
Tip: Hot water demand often accounts for 30-50% of total heat demand in well-insulated houses. With smart heating times, you can save 5-20% electricity by heating at midday instead of at night!
Step 2: Select Heat Pump
First choose the heat pump type:
| Type | Heat Source | Typical SPF | Features |
|---|---|---|---|
| Air-water | Outside air | 2.8-3.8 | Affordable, simple installation |
| Brine-water | Ground | 3.5-4.5 | Stable temperatures, higher investment |
| Water-water | Groundwater | 4.2-5.0 | Highest efficiency, permit required |
Option A: Select from catalog
- The catalog contains current models from renowned manufacturers
- Rated capacity, COP values and manufacturer specifications are stored
- Simply click on a model – done!
Option B: Manual entry
- For models not in the catalog
- Required: Rated capacity [kW] and COP A2/W35
- Optional: COP A-7/W35 (for cold days) and COP A7/W35 (for mild days)
Where can I find COP values? In the technical data sheet of the heat pump, on the BAFA subsidy list, or in the Keymark certificate. Pay attention to the correct flow temperature (usually W35 = 35°C).
Step 3: Configure System Parameters
Heating circuit temperatures:
| Parameter | Underfloor heating | Radiators | Old radiators |
|---|---|---|---|
| Flow | 30-35°C | 45-55°C | 60-70°C |
| Spread | 5-7 K | 7-10 K | 10-15 K |
Golden rule: The lower the flow temperature, the higher the SPF! Every Kelvin less brings about 2-3% more efficiency. Check if larger radiators are possible!
Hot water settings:
- Storage temperature: Default 55°C (minimum temperature according to drinking water regulations)
- Legionella prophylaxis: Weekly heating to 65°C (costs efficiency, but recommended)
Electricity price:
- Household electricity: approx. 28-35 ct/kWh
- Heat pump tariff: approx. 22-28 ct/kWh (with blocking times)
Understanding Results
Main Results
| Metric | Description | Good Values |
|---|---|---|
| SPF (Seasonal Performance Factor) | Average efficiency over the year | ≥3.0 (air), ≥3.5 (brine/water) |
| SCOP | European standard, corresponds roughly to SPF | ≥3.5 for A++ label |
| Electricity consumption | Annual consumption for heating + DHW | The lower, the better |
| Operating costs | Annual electricity costs | Comparison with gas heating useful |
SPF Rating:
| SPF | Rating | Comment |
|---|---|---|
| < 2.5 | ⚠️ Critical | Uneconomical, check system |
| 2.5-3.0 | 🟡 Adequate | Acceptable, optimization potential |
| 3.0-3.5 | 🟢 Good | Typical for air-source HP |
| 3.5-4.0 | 🟢 Very good | Good ground-source or optimized air-source HP |
| > 4.0 | ⭐ Excellent | Ground/water-source HP with low temperatures |
Monthly Breakdown
The diagram shows for each month:
- Heat demand [kWh]: How much heat is needed
- COP: How efficiently the heat pump operates in this month
- Electricity consumption [kWh]: Derived from heat demand / COP
Interesting: In summer, the COP is highest (warm outside air), but hardly any heating demand. In winter, it's the opposite – high demand with lower COP. The SPF is the weighted average over all months.
Important Input Parameters Explained
Reading COP Values Correctly
COP specifications in data sheets follow a standardized notation:
A2/W35 = Outside air 2°C, Flow 35°C
B0/W35 = Brine 0°C, Flow 35°C
W10/W35 = Groundwater 10°C, Flow 35°CTypical COP values of an air-water heat pump:
| Condition | Meaning | COP Range |
|---|---|---|
| A-7/W35 | Cold winter day | 2.0-3.0 |
| A2/W35 | Typical heating day | 3.0-4.5 |
| A7/W35 | Mild day | 4.0-5.5 |
Attention: COP at W35 (35°C flow) is significantly higher than at W55 (55°C). Always compare values with the same flow temperature!
Flow Temperature
The flow temperature has the greatest influence on the SPF:
| System | Flow | SPF Potential |
|---|---|---|
| Underfloor heating | 30-35°C | ⭐⭐⭐ Optimal |
| Wall heating | 35-40°C | ⭐⭐ Very good |
| Large radiators | 40-50°C | ⭐ Good |
| Standard radiators | 50-60°C | Acceptable |
| Old small radiators | >60°C | ⚠️ Critical |
Optimization tips:
- Replace radiators with larger ones → lower flow temperature possible
- Perform hydraulic balancing
- Lower heating curve (gradually, test comfort limits)
Hot Water Strategies 🆕
In the hot water assistant, you can choose not only the demand but also the heating strategy:
| Strategy | Description | Efficiency |
|---|---|---|
| ⏰ Continuous | Tank is kept warm around the clock | Reference |
| ☀️ Once daily | Heating at a fixed time (e.g., 12:00) | +5-15% |
| 🌅🌆 Twice daily | Morning and evening | +3-8% |
| 🌞 Solar-optimized | Automatically 10am-3pm (ideal with PV) | +10-20% |
| 🌙 Night operation | At night with night tariff | −5-15% |
Why does heating time make a difference?
The COP of the heat pump depends on the outdoor temperature. At midday it's warmer than at night – the heat pump works more efficiently. With intelligent heating times, you can save 5-20% electricity!
Tip for PV owners: Choose "Solar-optimized"! Hot water preparation between 10am-3pm uses your own solar power and benefits from higher outdoor temperatures.
Frequently Asked Questions
Why is my calculated SPF lower than the manufacturer's specification?
This can have several reasons:
- Higher flow temperature: Manufacturers often specify SPF at 35°C flow
- Colder location: Your design outdoor temperature is lower than the reference location
- High hot water share: DHW is prepared at higher temperature (65°C for legionella)
- Night operation DHW: Heating at cold outdoor temperatures lowers the SPF
What SPF do I need for BAFA funding?
As of 2024 (BEG):
- Air-water HP: SPF ≥ 3.0
- Brine-water HP: SPF ≥ 3.5
- Water-water HP: SPF ≥ 3.5
- Bonus for natural refrigerants (R290 Propane)
Is a heat pump worthwhile with radiators?
Yes, if:
- Flow temperature ≤55°C achievable
- SPF ≥ 3.0 realistic
- Electricity price ≤ 30 ct/kWh
Check the "Optimal flow temperature" with our Heating load calculator!
What is the difference between COP and SPF?
| COP | SPF | |
|---|---|---|
| Measurement | Laboratory, defined conditions | Real operation, 1 year |
| Period | Snapshot | Annual average |
| Significance | Comparison under standard conditions | Actual efficiency |
| Typical value | 3.5-5.0 (at A2/W35) | 2.8-4.5 |
Tips for Best Results
✅ Use heating load import: The combination of heating load and heat pump calculator delivers the most accurate results
✅ Optimize flow temperature: Check if larger radiators are possible – every Kelvin less brings 2-3% more efficiency
✅ Heat hot water smartly: Use the heating strategy "Solar-optimized" or "Once daily at midday"
✅ Check COP values: Pay attention to the correct flow temperature (W35 vs. W55) when comparing
✅ Save project: Note the project key – this allows you to compare variants later
Note: The calculated SPF is a forecast based on the entered data. The actual SPF also depends on user behavior, control system and installation. For binding calculations, consult a specialist planner.
To the heat pump guide with formulas and calculation principles →