Heat Pump Settings: The Practical Guide Icon

Heat Pump Settings: The Practical Guide

A heat pump is installed, running – and then what? Many owners rely on factory settings or the installer's initial configuration and never touch the system again. A mistake, as it turns out: A heat pump's efficiency depends critically on how well it's tuned to the specific building. And this tuning isn't a one-time task, but a process that spans one to two heating seasons.

This article is for everyone who wants to get more out of their heat pump – without expensive professionals, using simple means and some patience. We explain the key adjustments, debunk myths (such as individual room control), and provide a concrete roadmap for systematic optimization.

Heat Pump Optimization: Key adjustments at a glance

Why Optimization Matters

The initial setup by your installer is just a starting point. Experience shows: Systems that are systematically optimized over one to two heating seasons achieve 15–25% better efficiency than systems left untouched after installation.

The reason lies in the nature of things: Every building behaves differently. Insulation quality, orientation, user behavior, and even furniture placement affect heating demand. No installer can fully account for these factors during initial setup – they only become apparent during real operation.

What's Realistically Achievable?

Starting Point After Optimization Savings
SPF 3.0 (factory settings) SPF 3.8–4.2 €200–400/year
SPF 3.5 (good initial setup) SPF 4.2–4.5 €100–200/year

Heat pump optimization is an iterative process. You observe, adjust, observe again – and gradually approach the optimum. This article shows how to do this systematically.

The Heating Curve – Your Most Important Lever

The heating curve is by far the most important parameter for efficient heat pump operation. It determines what flow temperature the heat pump delivers at a given outdoor temperature.

The Principle

The basic idea is simple: The colder it is outside, the warmer the heating water needs to be. The heating curve defines this relationship.

Two parameters determine the curve:

Parameter Function Effect
Slope (Gradient) How strongly does flow temperature respond to outdoor temperature changes? Affects behavior in cold weather
Parallel Shift (Level) At what base level does the curve sit? Affects base temperature

Typical Starting Values

Different guide values apply depending on heating system and building type:

Heating System Slope Level Typical Flow Temperature
Underfloor heating, new build 0.3–0.5 2–4 28–35°C
Underfloor heating, older building 0.5–0.8 4–6 32–40°C
Low-temperature radiators 0.8–1.0 – 40–50°C
Conventional radiators 1.0–1.5 – 50–60°C

The golden rule: As flat and low as possible, as steep and high as necessary. Every degree less flow temperature saves 2.5–3% on electricity costs.

Practical Diagnosis

Observe your house over several days at different outdoor temperatures:

Symptom Cause Solution
Constantly too cold Base level too low Increase parallel shift (+1 to +2)
Constantly too warm Base level too high Reduce parallel shift (−1 to −2)
Only too cold in frost Slope too gentle Increase slope (+0.1 to +0.2)
Only too warm in transitional weather Slope too steep Reduce slope (−0.1 to −0.2)
Cold in morning, warm in afternoon Heating curve responds too slowly Adjust time program if needed

Practical Adjustment

Step 1: Document starting values Note the current settings and measured room temperatures at various outdoor temperatures.

Step 2: Make small changes Only change one parameter at a time and only in small steps:

  • Parallel shift: maximum ±1 per adjustment
  • Slope: maximum ±0.1 per adjustment

Step 3: Observe Wait at least 3–5 days before the next change. The building needs time to respond to the new setting.

Step 4: Document and repeat Keep a simple log. After one heating season, you'll have valuable data for fine-tuning.

Why Room Thermostats Are Counterproductive with Heat Pumps

With conventional heating systems, room thermostats are standard. With heat pumps, however, they can significantly reduce efficiency.

The Problem: Short Cycling

Heat pumps are controlled via the return temperature. When room thermostats close individual heating circuits, the volume flow in the system decreases. The consequence:

  1. The return temperature rises faster than expected
  2. The heat pump switches off (even though there's still heating demand)
  3. After a short time, it switches on again
  4. This cycle repeats – the system short cycles

The Consequences

Problem Impact
Inefficiency at startup In the first 3–5 minutes, COP is only 1.5–2.5 instead of 4+
Increased wear Compressor suffers from frequent on/off switching
Shortened lifespan From 20–25 years to 8–12 years with heavy cycling
Higher electricity costs Up to 17% SPF loss from cycling

Critical value: More than 3 starts per hour is considered problematic. At 8–12 starts per hour, premature wear is likely.

The Better Approach: Uniform House Temperature

Instead of controlling individual rooms via thermostats, the entire house temperature should be controlled via the heating curve:

  1. Fully open thermostatic valves in the reference room (living room or most-used room)
  2. Set the heating curve so this room reaches the desired temperature
  3. Only adjust other rooms via valves for extreme deviations (e.g., guest room permanently cooler)

The Misconception "Save Energy by Lowering Individual Rooms"

Many users believe they save energy by keeping unused rooms cold. With heat pumps, this is often wrong:

  • Heating up a cooled room requires high flow temperatures
  • High flow temperatures mean low COP
  • The extra consumption during heating often exceeds the savings

Better: A uniformly low temperature throughout the house (e.g., 20°C everywhere instead of 22°C in the living room and 16°C in the bedroom).

Hydraulic Balancing – DIY Guide for Underfloor Heating

Hydraulic balancing ensures that each heating circuit receives exactly the amount of water it needs. Without balancing, water flows preferentially through the shortest pipes – some rooms get too warm, others stay cold.

Why Especially Important with Heat Pumps?

Heat pumps even have a requirement for hydraulic balancing. The reason: These systems work with low flow temperatures and small temperature differences. Uneven flows have a greater impact here than with conventional heating.

Savings potential: Approximately 13% energy savings in the first year after balancing.

The Return Temperature Method (DIY)

This method requires no complex calculations and works with simple tools.

Required materials:

  • Infrared thermometer (€20–40) or contact thermometer
  • Documentation of your heating circuits (if available)
  • Patience and time (one weekend)

Preparation:

  1. Fully open all heating circuits at the manifold
  2. Set all room thermostats to maximum (if present)
  3. Set heat pump to constant, elevated flow temperature (e.g., 40°C)
  4. Let system run for at least 2 hours

Procedure:

Step Action Goal
1 Measure return temperature of each circuit at manifold Record current state
2 Calculate average of all return temperatures Determine target value
3 Throttle circuits with too high return temperature Even distribution
4 Wait 1 hour and measure again Check effect
5 Repeat steps 3–4 until all circuits are ±1°C from average Balancing complete

Interpreting measurements:

Result Meaning Action
Return significantly warmer than average Too much flow Close valve (¼ turn)
Return significantly colder than average Too little flow Open valve further
Return close to average Optimal No change

Target spread value: For underfloor heating, the difference between flow and return should be approximately 5–8 Kelvin. With 35°C flow, that would be a return of 27–30°C.

Cost Comparison

Option Cost Time Required
DIY (return method) €20–40 (thermometer) 4–8 hours
DIY (with RTL valves) €150–300 6–10 hours
Professional €600–900 –

Bivalence Point and Hybrid Optimization

For hybrid systems (heat pump + gas/oil boiler) or bivalent operation, the bivalence point is an important adjustment.

What Is the Bivalence Point?

The bivalence point is the outdoor temperature at which the heat pump's heating output exactly matches the building's heating demand. Below this temperature, the second heat generator must assist or take over.

Typical values: −2°C to −8°C (depending on heat pump and building)

Thermal vs. Economic Bivalence Point

There are two different perspectives:

Perspective Definition Typical Value
Thermal Temperature where HP output = heat demand −5 to −10°C
Economic Temperature where heat pump becomes more expensive than alternative −2 to −5°C

Calculating the Economic Bivalence Point

The heat pump is economical as long as its COP stays above the threshold COP:

Formula:

Threshold COP = Electricity price / (Alternative energy price / Efficiency)

Example with gas:

  • Electricity price: €0.30/kWh
  • Gas price: €0.10/kWh
  • Boiler efficiency: 95%

Threshold COP = 0.30 / (0.10 / 0.95) = 2.85

As long as the heat pump achieves a COP above 2.85, it's cheaper than the gas boiler. At what outdoor temperature this value is undercut depends on the heat pump type.

Practical Recommendation for Hybrid Systems

Situation Recommended Bivalence Point
Well-insulated house, efficient HP −5 to −8°C
Older building with higher demand −2 to −4°C
Dynamic electricity tariffs Use automatic control

Modern hybrid controls (e.g., Viessmann Hybrid Pro, Vaillant triVAI) automatically calculate the optimal switchover point from current energy prices. Savings compared to fixed settings are 10–25%.

Hot Water Optimization

Hot water preparation accounts for 15–25% of heat pump electricity consumption in many households. There's significant optimization potential here.

The Temperature Dilemma

Temperature Efficiency Legionella Risk
45–48°C Very good (low COP loss) Elevated
50–52°C Good Low
55–60°C Moderate (high COP loss) Very low

Recommended Settings

For single and two-family homes with short pipe runs:

  1. Normal storage temperature: 48–50°C
  2. Weekly legionella cycle: Heat to 60°C once per week (30 minutes)
  3. Optimize charging times: Preferably heat water when PV surplus is available

Efficiency gain: Approximately 15–20% less electricity consumption for hot water compared to constant 55°C.

Legionella note: In apartment buildings or with long pipe runs, stricter requirements apply. A constant temperature of at least 55°C and regular circulation is required.

Seasonal Optimization – The Two-Year Plan

Heat pump optimization is not a one-time task. Only after one to two complete heating seasons is the system truly tuned to the building.

Why Does It Take So Long?

  1. Building drying: New builds or freshly renovated buildings need 2–3 years to fully dry out. During this time, heating demand changes.

  2. Seasonal variation: A meaningful SPF can only be determined after a complete heating period. Mild winters distort the picture.

  3. Learning effect: You first need to learn how your house behaves at different outdoor temperatures.

Optimal Times for Adjustments

Season Outdoor Temperature Adjustment
Spring/Autumn 5–15°C Parallel shift (level)
Winter Below 0°C Slope
Summer – Hot water settings, evaluation

The 10% Rule

Never change settings by more than 10% of the starting value at once. With a slope of 0.5, that would be maximum ±0.05 per adjustment.

The Concrete Optimization Plan

Phase 1: First Heating Season (Months 1–6)

Period Action Expected Result
Week 1–2 Document current state: settings, room temperatures, electricity consumption Baseline for comparison
Week 3–4 Check/perform hydraulic balancing Even heat distribution
Week 5–8 Adjust heating curve in transitional weather (level) Comfort temperature without overheating
Week 9–16 In frost: Check slope and adjust if needed Sufficient heat even in cold
Week 17–20 Optimize hot water settings Legionella-safe with maximum efficiency
Week 21–24 Take stock, note problems Improvement list for next season

Phase 2: Summer (Months 7–9)

  • Observe hot water-only operation
  • Analyze documentation from first heating period
  • Record improvement ideas for next season
  • Refine hydraulic balancing if needed (rooms that were too warm/cold)

Phase 3: Second Heating Season (Months 10–18)

Period Action Expected Result
Week 1–4 Apply settings from previous year, observe Better start than last year
Week 5–12 Fine-tuning at various outdoor temperatures Extract final percentages
Week 13–20 Continue monitoring Stable, optimized SPF
Week 21–24 Final evaluation, compare with previous year Optimization complete

Phase 4: Long-term Operation

After the optimization phase:

  • Monthly: Check SPF (read electricity and heat meters)
  • Annually: Review settings for plausibility
  • After changes: Adjust heating curve after window replacement, insulation measures, or renovations

Monitoring and Success Control

Without measurement, no optimization. You need data to recognize progress.

Required Equipment

Component Purpose Cost
Heat meter Measures generated heat Often already installed
Electricity meter Measures HP power consumption €50–100 (sub-meter)
Thermometer Room temperatures, flow/return €20–40
Documentation Spreadsheet or app Free

Calculating SPF

The Seasonal Performance Factor is the most important efficiency indicator:

SPF = Heat output (kWh) / Electricity consumption (kWh)

Example:

  • Heat meter: 12,500 kWh
  • Electricity meter: 3,200 kWh
  • SPF = 12,500 / 3,200 = 3.9

Evaluating SPF

SPF Rating Recommendation
> 4.5 Very efficient Optimization successful, maintain
4.0–4.5 Efficient Good, possibly small improvements still possible
3.5–4.0 Acceptable Potential exists, check heating curve
3.0–3.5 Needs improvement Systematic analysis recommended
< 3.0 Problematic Consult professional

Additional Optimization Tips

Utility Blocking Times

Since 2024 in Germany: Energy suppliers may only throttle heat pumps to at least 4.2 kW (no longer completely shut off) – for a maximum of 2 hours daily.

Recommendation:

  • Size buffer tank: 40–80 liters per kW of heat pump output
  • Use reduced grid fees: €110–190/year savings

Night Setback – Yes or No?

Building Type Recommendation Reason
Well-insulated (Passive house) No setback Reheating costs more than savings
Moderately insulated 2°C setback Slight savings possible
Poorly insulated 3–4°C setback Noticeable savings (3–8%)

Important: Night setback is usually not sensible for underfloor heating due to its thermal inertia.

Common Mistakes to Avoid

Mistake Consequence Solution
Heating curve set too high Unnecessarily high flow temperature, low COP Gradually reduce
Individual room control too aggressive Cycling, wear Set thermostats to maximum, control via heating curve
No hydraulic balancing Uneven heat distribution Perform DIY balancing
Hot water too hot Low COP for DHW preparation 48–50°C + weekly legionella cycle
No documentation Optimization success not measurable Record meter readings monthly

Conclusion

Key Points:

  1. The heating curve is your most important lever – properly set, it saves 15–25% on electricity costs
  2. Room thermostats are usually counterproductive with heat pumps – uniform temperature control via the heating curve is more efficient
  3. Hydraulic balancing is mandatory – and doable as DIY
  4. Optimization is an iterative process over 1–2 heating seasons
  5. Monitoring is essential – you can't improve what you don't measure

A systematically optimized heat pump achieves a 15–25% better seasonal performance factor than a system set up only once. With an average electricity consumption of 4,000 kWh/year, that's savings of €200–400 annually – with minimal effort.

The investment of time in optimization pays off: A weekend for hydraulic balancing and regular small adjustments to the heating curve make the difference between a mediocre and an excellent system.

The Complete "Heat Pumps" Article Series

  1. Heat Pump: The Complete Guide 2026 – Overview
  2. The Reverse Refrigerator: How Does a Heat Pump Work? – Physical Principles
  3. The Components: Heat Exchanger, Compressor and Expansion Valve – Components in Detail
  4. Key Figures and Sizing of Heat Pumps – COP, SPF, SCOP
  5. Operating Modes: Monovalent, Bivalent and Hybrid – Operating Modes Explained
  6. Heat Pump Types and the Dream Team with Solar – Types & Combination with PV
  7. SCOP Explained: The Seasonal Coefficient of Performance – Properly Evaluating Efficiency
  8. Heat Pump Settings: The Practical Guide – You are here

Sources

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