Heating Replacement: Oil Boiler to Heat Pump (Air or Brine to Water)

Replacing an oil- or gas-fired heating system with an electric heat pump. Cuts final energy substantially (factor 3-4) and eliminates fossil fuel entirely.

How does switching from an oil boiler to a heat pump work?

A heat pump extracts low-temperature heat from the surroundings – outdoor air, the ground or groundwater – and raises it via a refrigerant circuit with a compressor to the temperature required for space heating and hot water. Electricity is only needed to drive the compressor. The ratio of heat delivered to electricity consumed over a whole year is known as the seasonal performance factor (SPF). Air-to-water heat pumps typically achieve 3.0 to 4.0, brine-to-water (ground source) systems with borehole drilling 4.0 to 4.8. One kilowatt-hour of electricity therefore becomes three to five kilowatt-hours of heat. An old oil boiler, by contrast, converts only 70 to 80 % of the fuel into useful heat. When replacing the boiler, the oil tank is decommissioned and the heat pump is connected to the existing water-based distribution system.

Which existing buildings are suitable for a heat pump?

What matters is less the year of construction than the required flow temperature. If it is around 50 °C or below, the heat pump operates efficiently – typically in insulated buildings, with underfloor heating or with generously sized radiators. A heating load below 50 W/m² serves as a rule of thumb. A simple practical test: if the building stays sufficiently warm during frost with a flow temperature of 55 °C, the switch is usually feasible. Typical buildings are detached and semi-detached houses, terraced houses, small apartment buildings, schools and office buildings up to around 2,000 m². Requirements are an electrical connection with spare capacity and an installation site with noise protection (air-to-water) or space for a borehole or ground collector (brine-to-water). Uninsulated older buildings with flow temperatures above 65 °C should first undergo thermal refurbishment; in listed buildings, outdoor units may be ruled out.

What does switching to a heat pump actually deliver?

Final energy consumption falls by 65 to 80 %, CO2 emissions by more than 90 % – to zero with green electricity. For a detached house with a heat demand of 18,000 kWh, this means around 19,700 kWh less final energy and about 5.7 t of CO2 per year. The investment is 18,000 to 32,000 € for air-to-water and 28,000 to 45,000 € for brine-to-water including borehole drilling. Over a 20-year service life, the system pays back in 8 to 15 years depending on subsidies and electricity prices.

Energy carrier

Heizöl → Strom

Savings potential

65-80 % Endenergie, >90 % CO2 (bei Ökostrom 100 %)

Worked example

A detached house with 150 m² gross floor area and a space heating demand of 100 kWh/(m²·a) requires 15,000 kWh of space heating plus 3,000 kWh for hot water – 18,000 kWh/a in total. The existing oil boiler operates at an annual efficiency of 0.75 and therefore consumes around 24,000 kWh of heating oil per year. A brine-to-water heat pump with a seasonal performance factor of 4.2 is chosen as the replacement. The final energy saving is 18,000 × (1/0.75 − 1/4.2) = 18,000 × (1.333 − 0.238) = 18,000 × 1.095 = 19,710 kWh/a. The new electricity consumption is 18,000 / 4.2 = 4,286 kWh/a. Using emission factors of 0.266 kg CO2/kWh for heating oil and 0.156 kg CO2/kWh for the Austrian electricity mix, the CO2 balance is 6,384 kg − 668 kg = 5,716 kg/a. The building therefore saves around 19,700 kWh of final energy and about 5.7 t of CO2 per year.

Investment & payback

Luft/Wasser: 18.000-32.000 €; Sole/Wasser inkl. Tiefenbohrung: 28.000-45.000 € (EFH) · Service life: 20 a · Payback: 8-15 (abhängig von Förderung und Strompreis) a

Applicability

Requirements

Exclusion criteria

Typical buildings

Frequently asked questions

How much does it cost to replace an oil boiler with a heat pump?

Replacing an oil boiler with a heat pump costs 18,000 to 32,000 € for an air-to-water heat pump in a detached house and 28,000 to 45,000 € for a brine-to-water system including borehole drilling. This includes the unit, installation, hydraulic integration and buffer tank. Additional costs arise for decommissioning the oil tank and, where necessary, upgrading the electrical connection. Payback is 8 to 15 years depending on subsidies and electricity prices, over a service life of around 20 years.

Do you need underfloor heating for a heat pump?

No, underfloor heating is not a mandatory requirement. What matters is that the building can be heated with a flow temperature of no more than around 50 to 55 °C. This is also achievable with radiators if they are sufficiently large or the building has been insulated. Hydraulic balancing and lowering the heating curve help to reduce the required flow temperature. For very high temperatures, high-temperature heat pumps are an option.

Is a heat pump worthwhile in an unrenovated old building?

In an uninsulated old building with flow temperatures above 65 °C, a heat pump usually only pays off after thermal refurbishment. The seasonal performance factor collapses at high flow temperatures, so electricity costs rise and the savings shrink. A staged plan makes sense: first insulate the envelope or enlarge the heating surfaces, then install the heat pump. A hybrid heating system, in which the existing boiler only covers peak load on cold days, can serve as an interim solution.

What is the difference between an air-to-water and a brine-to-water heat pump?

An air-to-water heat pump uses outdoor air as its heat source, while a brine-to-water heat pump uses the ground via a borehole or ground collector. The ground source heat pump achieves higher efficiency with a seasonal performance factor of 4.0 to 4.8 compared with 3.0 to 4.0 for the air source variant, because the source temperature remains stable in winter. However, at 28,000 to 45,000 € it is considerably more expensive than air-to-water at 18,000 to 32,000 € and requires space for drilling.

Which standards apply to heat pumps in Austria?

In Austria, the key standards for heat pumps are ÖNORM EN 14511 (testing and performance rating), ÖNORM EN 14825 (calculation of seasonal efficiency), ÖNORM M 7140 (economic calculation) and OIB Guideline 6 (the Austrian building code section on energy saving and thermal insulation). The methodology for assessing savings from boiler replacement is set out in the Austrian Energy Efficiency Guidelines Regulation 2016 (Energieeffizienz-Richtlinienverordnung). Subsidies for switching are offered by the federal government and the provinces and change regularly.

Related measures

Standards & sources

Metering points in the EDM Toolbox

Für EDM Toolbox empfohlene Messpunkte: (1) Stromzähler WP separat, (2) Wärmemengenzähler Vorlauf/Rücklauf, (3) Außentemperatur. So lässt sich die JAZ kontinuierlich monitoren. LineMetrics M-Bus Gateway für Wärmemengenzähler + Smart-Meter-API für WP-Strom geeignet.

All measures