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Home Heating with an Air-to-Air Heat Pump



Heating and cooling typically combine to be a home’s biggest energy use and its biggest contributor to greenhouse gases.  With super-efficient heat pump technology, however, you can stay comfortable and still tame your carbon footprint.  A bonus is that some heat pumps can also cool your home when it gets too hot.

Cost Range

DKK50,000 - DKK100,000

About the technology

Is it New?: Heat pumps have been used for heating and cooling for decades in some areas.  However, with improved technology (such as low-temperature heat pumps), they’re becoming more popular than ever and expanding into new regions.

How it Works: Heat pumps use electricity to move heat from one place to another, instead of creating the heat directly, as in a gas furnace or boiler. This is what makes them so efficient when compared to conventional heating systems.  

Applicable Types of Heat Pumps: Various types of heat pumps are available to match a home’s particular needs.  For example, air-to-air heat pumps (which can also provide cooling) can be used in many types of homes, including those with forced-air ventilation systems.  Air-to-water heat pumps are more compatible with homes containing hydronic heating systems that employ radiators or underfloor heating.  

Economics: Heat pumps are generally more expensive to install than a conventional space conditioning system, but incentives are sometimes available that can help with this higher cost. Also, you can sometimes save money on your energy bills going forward, especially if you’re switching from heating with electricity, propane/LPG, or oil.   If you combine a heat pump with rooftop solar, the economics can improve even more.

Environment: Heat pumps almost always help to reduce your greenhouse gas emissions. This is because they use electricity, and in a very efficient way.  Also, as grid-supplied electricity becomes cleaner over time, heat pumps will have an increasing environmental advantage over conventional heating systems.

Frequently Asked Questions (FAQ)

1. What is a heat pump?

A heat pump is a device that moves heat from one place to another but does not generate any heat of its own. Usually the flow of heat follows the temperature gradient from higher to lower temperature. However, a heat pump uses a compressor, heat exchangers, and other components to move the heat against a temperature gradient, much like a water pump moves water against the force of gravity. 

2. What are some everyday uses of heat pumps?

A refrigerator uses a small heat pump to move heat from inside your refrigerator to the surroundings, cooling your food. An air conditioner (AC), which moves heat from inside a house to the outside against a temperature gradient, is another example. Similarly, an air-to-air heat pump moves heat from inside to outside during the summer, functioning as an AC. In the winter, it has a mechanism to reverse the flow of heat and move heat from the outside your home to the inside, acting as a heater.

3. What are the major components?

A system has various components, including a compressor, outside and indoor heat exchangers, refrigerant (with associated piping), valves, and controls/wiring.  These components work with a forced-air system, such as a blower that transfers the heat/cool to the interior of your home.  Some heat pumps have integrated blowers and some rely on separate blowers and ducting.

4.What types of air-to-air heat pumps are available?

The most common forms of air-to-air heat pumps are: 1. “split” systems that rely on air ducts inside the house and a central heat exchanger to condition the air flowing through the ducts, and 2. ductless “mini-split” systems that use one or more registers inside the house to condition the space directly without using air ducts.  There are also other variations, such as ducted mini-splits, that can sometimes offer advantages. 

5. How does an air-to-air heat pump differ from a natural gas boiler?

First, an air-to-air heat pump provides not only space heating, but also cooling. By reversing the thermodynamic cycle, this one device can help keep you comfortable in both the winter and summer.  A heat pump is also more efficient because it’s designed to move heat, not create it.  Operationally, a heat pump takes longer to heat a home from a low temperature than does a boiler.  Accordingly, they’re generally used in a way that keeps a home at a more even temperature throughout the day and night.  

When it comes to carbon pollution, heat pumps have an advantage over other types of space heaters because of their greater efficiency.  The amount of the carbon reduction depends on the carbon intensity of the electricity used to power your heat pump and the energy source (such as natural gas, oil, electricity, etc.) you’re switching from.  If you add rooftop solar to your home, the carbon footprint of running a heat pump is drastically reduced.  

6. Can you set back the temperature when heating with an air-to-air heat pump?

It is advisable to use small setbacks with a heat pump since the heating process takes longer than with other forms of heating, such as a natural gas boiler.  By maintaining a relatively uniform temperature, the temperature recovery time is reduced.

7. Are mini-split systems more efficient than split systems?

In general, ductless mini-split systems are more efficient than split systems.  This is partly because they avoid the energy losses associated with ducting, which can be substantial in some cases. Also, the temperature setting of each register inside the house can be controlled separately, so the heating or cooling of the house can be more easily fine-tuned, thereby saving energy.  The efficiency of a ducted mini-split system generally falls in between a split system and a ductless mini-split.

1. How expensive are air-to-air heat pumps?

The installed cost of an air-to-air heat pump depends on a variety of factors, such as the type of heat pump, home size, location, existence of a forced-air duct system, need for additional wiring, etc.  Whilst they are typically more expensive than conventional systems, a HP may have lower operating costs, depending on the energy source you’re switching from. Also, it has the advantage of combining both heating and cooling into one system.

2. How much can I save on energy costs with a heat pump?

It depends on a number of factors, especially the type of system you’re switching from. If you’re replacing an electric or oil heating system, you should be able to cut your costs substantially. When replacing a boiler fueled by natural gas, however, if there is any reduction in your monthly costs, it would likely be small. If you also include a rooftop solar system, you can generate additional savings since the cost of the electricity needed to power the HP would be lower than the cost of grid-supplied power.

1. What kind of regular maintenance is needed?

Efficient operation of your heat pump generally involves periodic cleaning of debris and dust that has collected in and around coils, cleaning/replacement of filters, and checking of the condensate drain. Some experts suggest annual maintenance visits by a professional to avoid issues before they become full-blown problems.

2. If the heat pump cools and heats year round, does it wear out more quickly than an air conditioner?

Covering both winter and summer means that a heat pump will log more operating hours than a traditional air conditioning system.  Accordingly, it would normally have a shorter expected lifespan, but it would depend on how often the cooling function of the heat pump is used

1. Do heat pumps reduce greenhouse gases?

Yes, it will reduce your carbon footprint.  The amount of the reduction depends on the carbon intensity of the electricity used to power your HP and the energy source (such as natural gas, electricity, etc.) you’re switching from.  If you add rooftop solar to your home, the carbon footprint of running a HP can become negligible. Additionally, as grid-supplied electricity becomes cleaner over time, heat pumps will have an increasing environmental advantage over conventional heating systems.

1. How is an air-to-air heat pump installed?

This will depend on your current heating system and the type of heat pump being installed. For homes that currently have a hydronic (“wet”) heating system, the most straightforward approach is to install an air-to-water heat pump (as discussed in the Water Heating with a Heat Pump FAQ).  Installing an air-to-air HP in such a home would likely require either a radical change to the home’s heating system or inclusion of a mini-split HP as a parallel (supplemental) heating system. 

For a home without a hydronic heating system, the most applicable HP type would depend on whether ducts are currently in place.  If so, a central air-to-air HP would likely be selected, requiring the replacement of the indoor unit and installation of a new outdoor unit. If no ducts are currently in place, a mini-split would likely be selected, requiring the installation of an outdoor unit and one or more indoor registers.

2. Is a mini-split heat pump better than a central (split) system?

Mini-split systems are normally recommended if a house does not have air ducts or if extensive rework would be needed on the ducts.  Without the need for ducts, which can introduce significant energy losses, mini-splits are normally more efficient.  Mini-splits are also often recommended if only a portion of the home, such as several rooms, require heating.  In this case, a heating/cooling register can be economically placed in each of the rooms and tied to a single outdoor unit. If heating/cooling is needed for the whole house and existing ducts can be used, then a central HP system is generally recommended.

1. What types of incentives are available for air-to-air HPs?

Unfortunately, the subsidies available from the Building Pool program for air-to-water HPs (which are much more common in Denmark) aren’t available for air-to-air HPs.