One thing frequently mentioned about heat pumps is that their efficiency is vastly superior to that of oil or gas boilers. That’s how they end up saving you money, despite running on more expensive electricity.

The efficiency of a heat pump, or any heating system, is the ratio of how much heat it produces from the energy it consumes.

If a heat pump has an efficiency of 300%, that means it is delivering three units of heat to your home for every unit of electricity it uses to run.

The main selling point of heat pumps is that they are far more efficient than any other type of heating system. A heat pump typically produces 3 – 4 units of heat for every unit of electricity it uses. This gives them an efficiency of 300% – 400%.

In comparison, other heating systems can only produce a maximum of 1 unit of heat for every unit of energy or fuel used. Fossil fuel boilers are never 100% efficient since there is always some loss between the potential energy of the fuel they burn and what they deliver.

Measuring the efficiency of a heat pump differs from looking at a boiler or night storage heater because it is not constant. Burning oil or gas will always deliver the same amount of energy. The efficiency of a boiler only changes as it gets older and degrades.

However, a heat pump does not produce heat; it only moves it. This means that an air source heat pump will need to work harder to produce the same amount of heat when it is colder outside.

There are two main terms used to describe and measure the efficiency of a heat pump.

If a heat pump uses 1kWh of electricity to produce 4kW of heat, then it has a COP of 4.0. This would also be called an efficiency of 400%.

Most heat pumps used in Irish homes should have a COP of 3.0 – 4.0 during their regular operations.

In winter your heat pump will be working harder with a lower temperature heat source compared to summer. Because of this, the SCOP is a more useful measurement of the overall performance of a heat pump since it encompasses both the highs and lows of the system.

In order to maximise the efficiency of a heat pump you need to make sure that you have the right power system which is properly calibrated for its environment and heat output.

While we have been talking about a single figure for efficiency up until now, for the majority of people there are actually two figures for this. 

Most homes in Ireland use air-to-water heat pumps, and unless you have a hybrid system, the heat pump will be providing both space heating and domestic hot water.

This is relevant to the efficiency of your heat pump since water has a far higher heat capacity than air. Simply put, it takes more energy to change the temperature of water than it does with air.

This means that if you see an efficiency rating for domestic hot water (DHW) production for a heat pump, it will likely be significantly lower than its space heating efficiency.

Heat pumps run off electricity, which is always more expensive per kWh than oil or gas. This means that in order for a heat pump to save you money, it needs to be much more efficient than a boiler.

It is common to hear horror stories about people who have gotten the wrong heat pump installed, thinking that they could just replace their boiler with the same strength system. They’re then left wondering why their heating has become so much more expensive than it used to be.

On the surface, it looks like the efficiency of a heat pump makes it the clear choice over a new boiler every time. Unfortunately, it’s not quite that cut and dried. While heat pumps are, for the most part, a better choice, it depends on the right factors.

The efficiency of a heat pump must also be looked at in relation to the cost of the electricity it uses.

Heat pumps use electricity rather than burning fossil fuels directly, but that doesn’t mean there are no carbon emissions related to their usage.

Roughly 50% of Ireland’s electricity is still generated from natural gas. This figure changes depending on the output of renewable wind and solar sources at any given time. Therefore, the efficiency of a heat pump is directly related to its carbon footprint.