1 Kilowatt-hour is 1kWh.

It doesn’t matter whether it’s a kilowatt of electrical energy through an immersion heater, or a kilowatt from a boiler. One kilowatt-hour of heat energy, no matter where it comes from, will have much the same effect.

A single kilowatt-hour of energy will raise the temperature of a 100 litre hot water cylinder by 8.6°C. Or 200 Litres by 4.3°C, or 50 Litres by 17.2ºC.

A kilowatt-hour of energy, is equivelant to a 1 kilowatt appliance being left on for 1 hour. Or, a 500W Appliance for 2 hours. Or a 10kW boiler burning for 6 minutes. Or the output of the 1000kW engine of a Bugatti Veyron travelling at full speed for just under 4 seconds. All of these equal One Kilowatt-Hour (kWh). This is also, conveniently, a single unit of electricity, for billing purposes.

Energy is Energy.

What does it replace?

The first and most important thing you need to know when working out the benefits of your heat pump install, is to work out what it replaces. Energy that comes from a Heat Pump is energy that does not have to be provided by your existing, or backup, heating systems. 1 kWh of heat from your Heat Pump is 1 kWh of energy that does not have to come from your boiler.

In other words, from fuels you do not have to burn and money you do not have to spend

How much per Kilowatt-hour?

The SEAI has produced a document which gives the effective cost per kWh from various fuel-types. It’s summarised quickly in the table below.

You must, however, factor in the efficiency of your heating technology. Modern boilers can be up to 95% efficient, meaning 95% of the energy delivered from the fuel can be actually used. For older boilers this value can be as low as 75%, meaning that for every kilowatt-hour of fuel you pay for, up to a quarter of it goes to waste. Put more succinctly, a quarter of your fuel budget is being burned for no benefit to you whatsoever. In fact, this system will have to burn 1.3kWh worth of fuel, to achieve a 1kWh output.

Or, an increase in fuel consumption of a 33%.

Your boiler or appliance should come with an efficiency rating – from this you can calculate the actual cost of the fuel being burned to achieve a 1 kWh output from this system. Assuming an efficiency rating of 80%, the effective cost per-kWh from these appliances may be as high as.

Electrical heating systems such as Immersion Heaters, on the other hand, are effectively 100% efficient. 100% of the electrical energy goes towards heating. Howver, it can also be seen above that raw electricity, on a per-kWh basis, is the most expensive energy source by far.

How much does the energy from a Heat Pump cost?

Heat Pumps are electric devices, so draw power and energy from the National Grid. How heat pumps work has been discussed by us before. The energy you receive from a Heat Pump in a multiple of the energy used to drive the compressor. This is the Heat Pump’s Coefficient of Performance, or COP. Unlike the rating on a boiler, this is not a static figure. It varies depending on the difference between the output temperature of the heat pump and the ambient temperature of the atmosphere. The higher the difference, the less efficient the Heat Pump will be.

The Hitachi Yutaki heat pumps offered by Greentherm gives an average COP of above 4 under normal condtions, when matched to a well-designed heating system.

Or, for every 1 kWh of energy the Heat Pump uses, it gives you 4 kWh worth of heat out.  This means that, with a delivered electricty cost of – on average – 18c per Unit, the effective cost per-kWh of heat received is 4.5c.

Adding this to the above table, gives the following comparison:

Clearly then, the Yutaki heat-pump offers the best cost-per-kWh of any heat source.

1 kWh of energy from a heat pump is almost half the price of 1 kWh from Gas.

The Bottom Line.

1000kWh of heat from a gas boiler will cost you €82.

1000kWh of heat from a kerosene boiler will cost you €119.

1000kWh of heat from a heat pump will cost you €45.

The Average Irish home can require up to 30,000kWh of energy to heat, annually.

For more information.

Contact us. This is only a quick, generic overview. The exact results depend on many other factors – such as your lifestyle, specific heating system design characteristics and heat-loads of the building. We take these factors into account when we design our heating systems to ensure that you receive the best value for money, while still achieving low runnings cost and guaranteed, hassle-free comfort all year round.