If you’re thinking about installing a heat pump in your home it is important to know about the different types of systems on the market, their costs and benefits, in order to find the one which is right for your home and energy needs.

Heat pumps are becoming an increasingly common addition to Irish homes as an energy efficient heating alternative, both among new constructions and for homeowners looking to reduce their heating bills while also reducing the carbon footprint of their homes.

Air to Water Heat Pumps are the commonly used variety of domestic heat pumps in Ireland with their small footprint and lower costs than other systems.

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Table of Content

How Does an Air to Water Heat Pump Work

A heat pump works by taking heat from an external source and raising its temperature to something usable in your home. Air Source Heat Pumps take that energy from the outside air to put it to use inside your property.

This is then used to heat another medium. With an air to water heat pump that medium is the heat from the outside air and transferred through the system to produce hot water.

The outdoor fan unit draws in air, from which heat is absorbed by the refrigerant and compressed to raise it to a usable temperature. The refrigerant is cycled through the system, with the heat absorbed.

How Does an Air to Water Heat Pump Work

What is an Air to Water Heat Pump For

There are three main uses for an air to water heat pump, heating the internal space of your home when it is cold, cooling the same space during the summer, or creating hot water for use in showers and taps.

In its most commonly used form, an air to water heat pump is connected to the central heating system to circulate hot water through radiators or underfloor heating. Compared with boilers, which only come on for a limited amount of time, heat pumps are designed to be left on for long periods, and keep your home at a consistent temperature.

Air to Water heat pumps can also work in reverse during the summer, extracting heat energy from inside of your home and transferring it outside.

Many heat pumps are designed to work with both a central heating and hot water system. Heat Pumps can be connected to an existing domestic hot water tank, and many larger model freestanding interior units will come with a built-in domestic hot water tank.

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How Efficient Are Air to Water Heat Pumps

Heat Pumps are far more efficient than oil and gas boilers in terms of how much energy they produce for what they use to operate. As a rough rule of thumb, heat pumps create 3 – 4 units of heat for every unit of electricity used to run them. Some top-of-the-line models on the market now have efficiency rates of up to 500%.

This is far more efficient than any oil, gas, or electric boiler, which will typically have an efficiency rating of 90-99% with modern models.

As heat pumps typically circulate lower-temperature water than traditional heating systems, they are at their most efficient when working with large surface areas such as bigger radiators or an underfloor heating system.

In its most commonly used form, an air to water heat pump is connected to the central heating system to circulate hot water through radiators or underfloor heating. Compared with boilers, which only come on for a limited amount of time, heat pumps are designed to be left on for long periods, and keep your home at a consistent temperature.

Air to Water heat pumps can also work in reverse during the summer, extracting heat energy from inside of your home and transferring it outside.

Many heat pumps are designed to work with both a central heating and hot water system. Heat Pumps can be connected to an existing domestic hot water tank, and many larger model freestanding interior units will come with a built-in domestic hot water tank.

How Efficient Are Air to Water Heat Pumps

Data Source: Worcester-Bosch Gas Condensing Boilers / Grant Vortex Oil Condensing Boilers / Viessmann Electric Boilers / Vaillant Arotherm Plus Heat Pumps

Types of Heat Pumps

There are two main variations of air to water heat pump systems, a Split heat pump and a Monobloc heat pump. The main difference between the two of these is whether they have an indoor unit in addition to the outdoor unit.

In its most commonly used form, an air to water heat pump is connected to the central heating system to circulate hot water through radiators or underfloor heating. Compared with boilers, which only come on for a limited amount of time, heat pumps are designed to be left on for long periods, and keep your home at a consistent temperature.

Air to Water heat pumps can also work in reverse during the summer, extracting heat energy from inside of your home and transferring it outside.

Many heat pumps are designed to work with both a central heating and hot water system. Heat Pumps can be connected to an existing domestic hot water tank, and many larger model freestanding interior units will come with a built-in domestic hot water tank.

Monobloc Heat Pump

In a monobloc air to water heat pump, all of the essential elements of the system are contained in the outdoor unit. This includes the refrigerant, compressor, heat exchanger, and water system. The hot water is piped from the outdoor unit back into the property.

Split Heat Pump

In a split air to water heat pump, there are two separate units, an exterior unit and an interior unit. The exterior unit absorbs heat from the outside air and heats the refrigerant. This is then piped to the interior unit where another heat exchanger connects it to the indoor heating system or hot water tank.

The benefit of a split heat pump is that it allows the outdoor unit to be located further from the property than with monobloc heat pumps, reducing noise disturbance.

Split Heat Pump

Heat Pump Components

There are multiple components to any heat pump system, some of which are common across all types, and some of which are relevant only to air source heat pumps.

The condenser is the heat exchanger which takes the energy from the high-pressure, high-temperature gaseous refrigerant and transfers it to the water system. It then cools and discharges the refrigerant as a liquid once again.

The Evaporator is the heat exchanger in a heat pump which allows the refrigerant to become gaseous and reach a higher temperature as it absorbs the energy captured from the air.

The compressor is used to compress the refrigerant to raise its pressure and temperature as it condenses into usable heat for the inside of the property. The compressor is the main use of electrical energy in a heat pump.

The expansion valve lowers the pressure and the temperature of the refrigerant at the end of the heat cycle into a state which is part liquid and gaseous as it returns to the beginning of the loop.

The Reversing Valve is used to reverse the flow of the refrigeration cycle in a heat pump, converting it from a heating system into a cooling system.

This is the element in the outdoor unit of air to water heat pumps which draws in a steady flow of air for its heat to be absorbed by the refrigerant.

Heat Pump Components

What is the Cost of an Air to Water Heat Pump

The cost of a heat pump depends on numerous factors including the size of your home, the number of rooms to be heated, and the size of the system needed to deal with that.

Air source heat pumps are typically the cheapest of the three main types compared with ground or water source systems, as they require less installation work.

The average cost of an air source heat pump will be in the region of €8,000 to €17,000 before considering the SEAI grant.

The cost of having an air to water heat pump installed can also depend on whether any other renovations or upgrades are needed in your home heating system at the same time. If your radiators are not large enough they might need to be replaced, and many homeowners undertaking larger retrofits might also take the opportunity to install underfloor heating.

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Heat Pump Energy Costs

Operating a heat pump will cost in the region of €500 – €1,000 depending on the size of the system, your home, and the heat levels it is set at.

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What to Look for When Buying a Heat Pump

There are a number of things which you should look at carefully when choosing a heat pump model, as you will have to live with it for a long time to come.

System Size

One of the most common mistakes people can make when purchasing a heat pump is getting a system which is too small or too large in power output. An undersized heat pump will not be effective at heating your home. Rooms further away from the heat pump will be colder than rooms closer to the indoor unit.

Worse still is potentially oversizing the system. Not only will this cost you more upfront, but it will also reduce your energy efficiency and cost more to run. Heat pumps are designed with a minimum operating output. This means that an oversized system will be shutting on and off regularly as it dumps large amounts of heat rather than maintaining a steady temperature.

Aesthetics

Any air source heat pump will come with a large visible outdoor unit, so it’s good to keep in mind whether you want to look at an ugly grey block. Makers such as Daikan have become more conscious of this and are making sleeker units which blend in with the property.

Refrigerant

The refrigerant is the substance which is used in the heat transfer system of the heat pump, absorbing heat from outside and releasing it indoors, or vice versa. Refrigerants such as R-410a should be avoided due to being terrible for the environment.

Many modern systems will use R-32 as a more environmentally friendly alternative in the same class as R-410a. But this is also being edged out now by R-290 or R-744 as non-toxic, easily available alternatives.

The environmental impact of refrigerants is measured by their Global Warming Potential, with Carbon Dioxide being the baseline GWP of 1.

Refrigerant Type Chemical Name GWP
R-410a HFC N/A 2,088
R-32 HFC Difluoromethane 675
R-290 HC Propane 3
R-744 N/A Carbon Dioxide 1

FAQs

Yes, if you have both solar panels and a heat pump installed in your home you can use the solar PV for the small amount of energy required to operate the heat pump, completely removing any fossil fuel use or carbon emissions.

Air source heat pump systems typically do not need planning permission as they cause the least disturbance to the fabric of the building or the grounds of the property.

While it might seem doubtful that air source heat pumps are a worthwhile investment in the Irish climate, they are more than capable of extracting heat energy even from as cold as -15 degrees.

The size of the heat pump needed for your home will depend on its floor space, the number of rooms, and how well-insulated it is. The majority of domestic heat pumps will be in the region of 4kW – 16kW for very large homes.

The SEAI offers grants of up to €6,500 for homeowners to invest in energy efficiency by installing heat pumps in their homes, subject to certain heat loss requirements.

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