Air to water heating

Air-water heat pumps are rarely recommended for heating churches. It is usually very difficult and very expensive to convert the heating system, so that the church can be heated satisfactorily with a water heating system and a heat pump.

Periodically heated churches

The heating system in a periodically heated church must have considerably higher output than other buildings of the same size. This is because the Ministry of Ecclesiastical Affairs’ Heat Circular requires that the church can be heated from 6° C to 18° C in just six hours. An underscaled heating system extends the heating time and energy consumption increases. The risk of damages to the church's furnishings and décor also increases.

Heating a church using an air-water heat pump, typically requires an output of 30 to 80 kW, depending on the church's size and condition. At the same time the heating system must be dimensioned to provide this output at a relatively low flow temperature, usually around 55° C. This requires many large radiators and convectors, which can be difficult to find room for in the church building.

Air to water heat pump as a partial solution for churches with basic heat

Some periodically heated churches have base heat, typically at 8˚C, which is the temperature prescribed by the Ministry of Ecclesiastical Affairs’ Heat Circular. Some churches, however, have a higher base temperature - and correspondingly higher energy consumption.

Base heating typically accounts for 20-40% of the total energy consumption in the church. A small air-water heat pump, installed in combination with the existing heating system, could provide this base heating. This may be especially relevant if the church is heated by oil or gas, and if the conditions for installing an air-water heat pump are present.

Permanently heated churches

A permanently heated church needs relatively less heat output compared to a periodically heated church of the same size, but it still needs a large heating system compared to other buildings. Furthermore, permanently heated churches are often larger churches, which requires correspondingly larger heating systems. The output should normally be 65 to 70 kW for a permanently heated church with a volume of about 2,000 cubic meters.

In many of the largest churches, the heating distribution system is often considerably underscaled. This requires a very high flow temperature (70-80 ˚C), to raise the church temperature within a reasonable timespan. This is not possible with an air-water heat pump.

In small permanently heated churches an air-water heat pump can sometimes be a solution, but it requires (among other things) a suitable location for the outdoor unit. At the same time the heating distribution system (radiators or calorifiers) must be reasonably well-dimensioned.

Placing the outdoor unit

Outdoor unit placement must be carefully considered, as there are both aesthetic considerations and noise limits to comply with. Regarding neighbours, the Danish Environmental Protection Agency has noise limits, but the municipality may choose to impose other limits. Regarding the cemetery, there may be locations that are undesirable due to noise.

It is important that the outdoor unit is placed in the open air, to ensure a good supply of fresh air. Attics or similar places are generally not recommended. If a foreclosure is built for the outdoor unit, it must be very open. If sufficient ventilation isn’t ensured, energy consumption will be unnecessarily large.


An annual inspection is mandatory because the system contains over 1 kg refrigerant.


Annual heating savings of 50% or more are typically achieved by heating with an air-water heat pump instead of an older oil-fired boiler. The payback time is typically about 10 years, but can vary between 5 and 15 years depending on local conditions.

Savings are only achieved if the heat pump is properly sized (complying with the recommendations of the Ministry of Ecclesiastical Affairs’ Heat Circular).


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