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Water Heating with a Heat Pump

Most homes still use fossil fuel or an inefficient electric system for water heating.  However, many people are now selecting super-efficient heat pumps to replace their aging systems.  Heat pumps can be three to four times as efficient as the older technologies and are often the best option for low operating cost & low impacts on climate.

Cost Range

€12,000 - €18,000

(for water & home heating)

About the technology

Is it New?: Not really — heat pumps have been around for years. For example, your refrigerator is one, and air conditioners are also heat pumps. However, the widespread application to home water heating is somewhat recent in many areas.

How it Works: Heat pumps use electricity to move heat from one place to another, instead of creating the heat directly. 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, some draw heat from the ground, some from well water, and some (the great majority) from the ambient air.  Additionally, some are designed to just supply domestic hot water (such as for showers, etc.) and others also supply hot water for home heating through radiators or underfloor heating. 

Economics: Heat pumps are generally more expensive to install than a conventional system.  In many areas, however, incentives are available that can defray this additional cost. Additionally, you can often save money on your energy bills going forward, especially if you’re switching from heating with electricity, propane/LPG, or oil.   

Environment: Heat pumps are a great way to reduce your carbon footprint.  Their excellent efficiency, combined with the fact that they don’t burn fossil fuels, often lets them cut greenhouse gas emissions by 75% or more.  Plus, as grid-supplied electricity becomes cleaner, the percentage reduction will grow over time.

Frequently Asked Questions (FAQ)

1. How does a heat pump work?

Instead of creating heat through fossil fuel combustion or electric resistance heating, heat pumps (HPs) use electricity to move heat from one place to another.  This process makes HPs very efficient — three to four times more so than other heating technologies — and can significantly cut heating costs in some cases.   Heating water with a HP is accomplished with an air-to-water HP, which moves heat from the ambient air into a hot water system that can be used for domestic hot water (showers and such) and/or home heating (such as with radiators or underfloor heating).  

2. What types of heat pumps are available for heating water?

Heat pumps can provide hot water for both heating your home and your domestic hot water (showers and such).  When both heating needs are provided, the HP system will typically consist of an outdoor unit that absorbs heat from the air and transfers it to: a) indoor radiators or underfloor coils and b) an indoor hot water cylinder for domestic hot water.  When a HP is used for only heating domestic hot water, a specialized heat pump water heater (HPWH) can be used.  These often consist of a single unit that combines a hot water cylinder with the HP components attached at the top.  HPWHs can also include heat exchangers that allow for the introduction of heat from other energy sources (such as a gas/oil boiler) as part of a hybrid heating system.

3. How much domestic hot water is available for the household with a heat pump?

This depends, to a large extent, on the cylinder size for domestic hot water storage.  The larger the cylinder, the more hot water you’ll have stored for use.  It should be noted that after being depleted of hot water, a cylinder will take longer to recharge using a HP than using a conventional water heater fueled by electricity or a fossil fuel.  As a result, some professionals suggest compensating for this longer recharge time by replacing your old cylinder with a somewhat larger one to provide additional water storage.  Most stand-alone heat pump water heaters are equipped with an electric-resistance backup capability, allowing them to recharge more quickly, but at a significantly reduced efficiency when this is employed.  

4. What are the advantages of using a heat pump for water heating?

Heat pumps use a proven, energy-efficient technology for heating. If you are switching from electric water heating or oil, a HP can reduce your water heating costs substantially.  If replacing natural gas, you may reduce your monthly water-heating costs, but the savings may not be large. Pairing the HP with a rooftop solar system can generate substantial savings since the cost of the electricity needed to power the HP is lower.  Also, there’s an environmental advantage to using a HP.  Your carbon footprint will be reduced, especially if your HP is powered by clean electricity, such as from solar or wind.

1. How much does an air-to-water heat pump cost?

The installed cost of a heat pump is significantly higher than the cost of a conventional electric or fossil-fueled system.  For example, a system covering both home heating and domestic hot water is likely to cost you between €12,000 and €18,000However, in some cases grants for such systems are available through the Heat Pump System Grant and can help cut the cost by up to €6,500, dramatically improving a HP’s cost effectiveness.  Depending on the energy source you’re switching from, your HP may have lower operating costs, cutting your monthly bills right away. Numerous site-specific factors affect the installed and operating costs of a HP, so it’s always a good idea to get cost estimates from local professionals.

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 system, you should be able to cut your water heating costs substantially. If replacing a boiler fueled by mains gas, however, any reduction in your monthly water-heating costs will likely be small. Pairing the HP with a rooftop solar system can generate significant savings since the solar power will be less expensive than electricity from the grid.

1. What are the steps needed to install a heat pump to heat water?

When both home heating and domestic hot water are provided, the HP system will typically include an outdoor unit that absorbs heat from the air and indoor components that transfer the heat to the water inside your home.  When only domestic hot water is supplied, the entire system can be combined into a stand-alone heat pump water heater that contains all of the HP components, plus the hot water cylinder, in one indoor unit. Planning permission is sometimes required for the installation of a HP. 

2. Where can I install a heat pump for heating water?

A standard heat pump will require an outdoor unit that could be slightly noisy, so placement away from a window or patio can be desirable.  For a standalone heat pump water heater (HPWH) that supplies just domestic hot water, a utility room is a likely location.  Since the HP components are bundled with the storage cylinder in a HPWH, the associated noise would be less troublesome than if the location was an interior closet.  These HPWHs also release cold air as they capture heat from their surroundings, which can be another drawback to an interior location (for HPWHs that aren’t vented to an unheated area).

1. What maintenance does a heat pump require?

Efficient operation of your heat pump generally involves periodic cleaning of debris and dust that has collected in and around coils. In some cases filters need to be cleaned/replaced, and the condensate drain needs to be checked. Some experts suggest annual maintenance visits by professionals to avoid issues before they become full-blown problems.

1. Can I save on carbon emissions if I switch to a heat pump?

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 at the same time, 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 do I operate a heat pump?

It’s often advisable to avoid large temperature setbacks, such as when you set your thermostat’s nighttime temperature.  This is because heat pumps take longer to heat your house than other forms of heating, such as a natural gas boiler.  By maintaining a more uniform temperature throughout the evening, it takes less time in the morning to reach a comfortable temperature.

1. What types of incentives are available for air-to-water heat pumps?

Grants of up to €6,500 are available for air-to-water HPs that provide both home heating and hot water.  Funding is through the Heat Pump System Grant and is administered by the Sustainability Authority of Ireland.