Retrofitting a heat pump in an old building: step by step

Would you like to equip your old building with a heat pump and save on heating costs? However, many homeowners are reluctant to take this step. They fear high costs or technical problems. These concerns are unfounded with proper planning and expert advice. In this article, you will learn step by step how to prepare your old building for a heat pump.

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Is the old building suitable for the heat pump?

Before you can start retrofitting, you need to make sure that your single-family home is suitable for a heat pump. Not every old building is suitable for operating a heat pump without adjustments. Eligibility depends on various factors. This includes the insulation standard, the existing heating system and the energy consumption of your building.

You can use the following checklist to make an initial assessment. It helps you to assess whether your building is generally suitable for a heat pump. If you are uncertain, you should consult an energy consultant.

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Evaluation:

• Mostly ✓: Your old building is well suited for a heat pump
• Mixed ✓/⚠: A heat pump is possible, but adjustments or refurbishment measures are necessary
• Mostly ⚠/✗: Extensive refurbishment required before heat pump installation

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Retrofit a heat pump in an old building in 9 steps

An orderly process ensures the success of your heat pump installation. Each step builds on the previous one. Don't skip a step. In this way, you avoid expensive mistakes and ensure that your heat pump functions optimally.

The following nine steps will guide you systematically through the entire process. From initial analysis to final optimization. Plan around 3 to 6 months for the entire project. You'll need most of the time for planning and approvals.

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Step 1: Current situation analysis and energy advice

You start with a thorough analysis of your current energy consumption. Collect your heating bills for the last three years. Document your existing heating system. Evaluate your building's insulation standard.

What you need to check:

• Annual consumption of heating energy (kWh or liter of oil/m³ gas)
• Age and condition of the current heating system
• roof, wall and basement insulation
• Condition of windows and doors
• size and type of existing radiators

recommendation: Hire a certified energy efficiency expert for a energy consulting. They will prepare a professional analysis and help you apply for funding.

The energy consultation costs between 500 and 1,500 euros. This investment is worthwhile. You will receive a well-founded assessment of your building. The expert will show you restructuring measures. It calculates the possible savings with a heat pump.

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Step 2: Calculate heat load

Die Heat load calculation is more important than the pure living space of your house. It determines the output of your heat pump. A heat pump that is too small will not be able to heat your house sufficiently. A heat pump that is too large works inefficiently and costs unnecessarily much.

Why the heat load is so important: The heat load indicates how much heat your building requires at the lowest outside temperature. It is expressed in kilowatts (kW). The calculation takes into account all heat losses. This includes losses through walls, windows, roof and ventilation.

Have the heat load calculated by a qualified company. The calculation is carried out room by room in accordance with the DIN EN 12831 standard, taking into account all relevant factors:

• external walls and their insulation
• Window surfaces and glazing
• roof and basement insulation
• Air exchange and ventilation losses
• Desired room temperatures

To give you a better feeling, you can use the following experience for an initial estimate:

• Well-insulated old buildings: 50-80 watts per square meter
• Partially insulated old buildings: 80-120 watts per square meter
• Uninsulated old buildings: 120-200 watts per square meter

These values are only a rough guide. An exact calculation is essential when designing your heat pump.

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Step 3: Check radiators or floor heating

yours existing radiator must often be replaced or supplemented. Heat pumps operate at lower flow temperatures than conventional heating systems. Old radiators are usually designed for flow temperatures of 70 to 90 °C. Heat pumps work optimally at 35 to 50 °C.

When you need to replace radiators:

• For small, old ribbed radiators
• If the flow temperature is above 55°C
• If the heating capacity of the existing radiators is insufficient

Solutions for your heating system:

• Low temperature radiator: These special radiators have a larger surface area. They emit sufficient heat even at low flow temperatures. The exchange is usually easy.
• Retrofit floor heating: Underfloor heating is ideal for heat pumps. It works with very low flow temperatures. Retrofitting is possible in old buildings, but requires more effort.

Step 4: Select heat pump type

You can choose between three main types of heat pumps. Each type has specific advantages and disadvantages. Certain systems are more suitable than others for old buildings.

• Air to water heat pump: This heat pump uses outdoor air as a heat source. It is the easiest to install. Investment costs are the lowest. However, efficiency decreases at very cold temperatures.
• brine water heat pump: This heat pump uses the constant earth temperature. It works very efficiently. However, the installation requires earthwork or drilling.
• Water-to-water heat pump: This heat pump uses groundwater as a heat source. It achieves the highest efficiency. However, the installation is complex and not possible everywhere.

The following is an overview of the advantages and disadvantages of each type of heat pump:

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An air-water heat pump is best suited for most old buildings. It offers the best balance of costs and benefits. A hybrid solution can be useful for very poorly insulated buildings. The heat pump is combined with a gas condensing boiler.

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Step 5: Apply for funding

They can significantly Subsidies for your heat pump received. The Federal Funding for Efficient Buildings (BEG) supports heating replacement with up to 70% of the costs. There are also regional funding programs.

Important: You must apply for funding before commissioning. Funding is no longer possible after the contract has been concluded.

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Step 6: Get planning and offer

You should obtain at least three offers from qualified specialist companies. Don't just pay attention to the price. The quality of planning and installation is decisive for the subsequent operation of your heat pump.

How to find the right specialist company:

• Look for companies with heat pump certification
• Ask for references and view completed projects
• Pay attention to membership in professional associations (BWP, ZVSHK)
• Check your experience with renovations of old buildings

The specialist company needs this data:

• Floor plans and building plans
• Energy certificates and consumption data
• Photos of the current heating system
• Information on planned restructuring measures
• Results of the heat load calculation

What to look for when it comes to offers:

• Detailed list of all components
• Information on the annual performance figure (JAZ)
• Hydraulic diagram of the planned plant
• Installation and start-up schedule
• Guarantees and services
• Costs for hydraulic balancing and adjustment

Warning signs for offers:

• Very low prices with no apparent reason
• No heat load calculation or hydraulic planning
• Pressure to make quick decisions
• No references or certifications
• Incomplete or unclear service description

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Step 7: Have the heat pump installed

It usually takes 2 to 5 days to install your heat pump. The exact process depends on the type of heat pump selected and local conditions. Good preparation reduces installation time.

Typical installation process:

• Day 1: Preparation and dismantling
  • Shutting off the old heating system
  • Draining the heating system
  • Dismantling the old heater
  • Preparation of installation areas
• Day 2-3: Installing the main components
  • Installation of the outdoor unit (with air-water WP)
  • Installing the indoor unit
  • Laying the refrigerant lines
  • Connection to the heating system
• Day 4: Electrical installation
  • Heat pump electrical connection
  • Installation of control technology
  • Connection of sensors and sensors
  • Programming the controller
• Day 5: Start-up and test
  • Filling and venting the system
  • Functional testing of all components
  • Setting the parameters
  • Test run and optimization

Typical interventions in your building:

• Openings for refrigerant lines (usually 2-3 holes)
• Electrical connections and control cables
• Adjustments to the heating distribution system
• Installing new radiators (if necessary)

What you should keep in mind during installation:

• Provide free access to all installation areas
• Plan alternative heating options for installation time
• Be available for inquiries from the installer
• Document progress with photos

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Step 8: Adjust and hydraulically adjust the system

The hydraulic balancing is crucial for the efficiency of your heat pump. Without proper adjustment, your heat pump can consume up to 30% more electricity. Each room must receive the right amount of heating water.

During hydraulic balancing, the installer calculates the optimal flow rate for each radiator. It adjusts the thermostatic valves accordingly. The circulation pump is programmed to the correct output. The entire system is coordinated.

Why hydraulic balancing is so important:

• Even heat distribution in all rooms
• Reduce power consumption by up to 15%
• Avoiding flow noises
• Longer heat pump life
• Optimum use of funding

The heat pump must be adapted to your building and usage patterns. The installer programs the heating curve. It sets the hot water temperature. The time programs are adjusted to your habits.

Have the settings explained and documented. You should know the most important parameters. This includes the flow temperature and the heating curve. You need this information for subsequent optimizations.

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Step 9: Monitoring and optimization

After installation, the optimization phase begins. Observe carefully how your heat pump is performing during the first heating season. Note down any abnormalities. If necessary, have the settings adjusted by a specialist company. Modern heat pumps also offer extensive monitoring functions.

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Combination with photovoltaic

A photovoltaic system significantly increases the efficiency of your heat pump. You can use your self-generated electricity directly for the heat pump. Intelligent control systems automatically optimize self-consumption.

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Special heat pump electricity tariff

Many energy suppliers offer special Electricity rates for heat pumps on. These are cheaper than normal household electricity rates. You need a separate meter or a two-rate meter for this.

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Regular maintenance

Leave your Maintain the heat pump annually. Maintenance includes cleaning the filters and checking the refrigerant charge. Settings are also checked and optimized.

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Smart home integration

Connect your heat pump to a smart home system. This allows you to monitor and optimize operations. Many systems offer apps for smartphones and tablets. They show you consumption data and efficiency values.

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Avoid common mistakes

Many homeowners make avoidable mistakes when installing heat pumps. These can significantly reduce efficiency or lead to high follow-up costs. By knowing the most common problems, you can avoid them from the outset.

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Mistake 1: Oversizing the heat pump

The problem: Many installers choose the heat pump too big. They are based on the living space instead of on the actual heating load.

The consequences: Higher purchase costs, inefficient operation, frequent frequency of the heat pump.

How to avoid it: Insist on a professional heat load calculation in accordance with DIN EN 12831.

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Mistake 2: Neglecting hydraulic balancing

The problem: The hydraulic adjustment is skipped or only carried out on a superficial level.

The consequences: up to 30% higher power consumption, uneven room temperatures, and noise generation.

How to avoid it: Have the hydraulic adjustment confirmed in writing and check that it has been carried out.

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Mistake 3: Incorrect positioning of the outdoor unit

The problem: The outdoor unit is placed too close to walls or neighboring buildings.

The consequences: Reduced efficiency due to air short circuit, noise problems with neighbors.

How to avoid it: Keep a distance of at least 3 meters from walls and 5 meters from neighboring windows

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Mistake 4: Inadequate insulation before installation

The problem: The heat pump is installed without first optimising the building envelope.

The consequences: high flow temperatures required, poor efficiency, high operating costs.

How to avoid it: First renovate the building envelope, then install the heat pump.

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Mistake 5: Abandoning professional planning

The problem: Homeowners choose the cheapest offer without sufficient planning.

The consequences: Inappropriate heat pump, operational problems, high repair costs.

How to avoid it: Invest in professional planning by certified specialist companies.

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Mistake 6: Failure to consider water heating

The problem: The hot water requirement is not correctly taken into account in the design.

The consequences: Inadequate hot water temperatures, risk of legionella, loss of comfort.

How to avoid it: Plan water heating right from the start.

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Conclusion: Heat pump in old buildings — feasible with good planning

Retrofitting a heat pump in an old building is certainly feasible and makes economic sense. Careful planning and professional implementation are decisive for success. You must honestly evaluate your building and, if necessary, renovate it beforehand. With the right preparation, you can reduce your heating costs by 50 to 70%. The high subsidies make the investment particularly attractive. Don't be afraid of the hassle of planning. A well-planned heat pump will serve you reliably and efficiently for many years. Get advice from experts and get multiple offers. This is how you can find the ideal solution for your old building.

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