Predicting the heat demand of a building, and therefore the performance and running costs of heating systems, is difficult to predict with certainty due to the variables discussed here. These variables apply to all types of heating systems, although the efficiency of heat pumps is more sensitive to good system design and installation. For these reasons your estimate is given as guidance only and should not be considered as a guarantee.

MCS Seasonal Coefficient of Performance (SCoP) is derived from the EU ErP labelling requirements, and is a theoretical indication of the anticipated efficiency of a heat pump over a whole year using standard (i.e. not local) climate data for 3 locations in Europe. It is used to compare the relative performance of heat pumps under fixed conditions and indicates the units of total heat energy generated (output) for each unit of electricity consumed (input). As a guide, a heat pump with a MCS SCoP of 3 indicates that 3 kWh of heat energy would be generated for every 1 kWh of electrical energy it consumes over a ‘standard’ annual cycle.

An Energy Performance Certificate (EPC) is produced in accordance with a methodology approved by the government. As with all such calculations, it relies on the accuracy of the information input. Some of this information, such as the insulating and air tightness properties of the building may have to be assumed and this can affect the final figures significantly leading to uncertainty especially with irregular or unusual buildings.

We have identified 3 key types of factor that can affect how much energy a heating system will consume and how much energy it will deliver into a home. These are ‘Fixed’, ‘Variable’ and ‘Random’. Most factors are common to ALL heating systems regardless of the type (e.g oil, gas, solid fuel, heat pump etc.) although the degree of effect varies between different types of heating system as given in the following table. The combined effect of these factors on energy consumption and the running costs makes overall predictions difficult however an accuracy + 25-30% would not be unreasonable in many instances. Under some conditions even this could be exceeded (e.g. considerable opening of windows). Therefore it is advised that when making choices based on mainly financial criteria (e.g. payback based on capital cost verses net benefits such as fuel savings and financial incentives) this variability is taken into account as it could extend paybacks well beyond the period of any incentives received, intended occupancy period, finance agreement period etc.

In most cases, air source heat pump installations are classed as ‘permitted development’ - meaning you don’t need planning permission. It’s worth noting, though, that there is still guidance to be met, such as the unit being at least 1 metre from the property boundary, and if you live in a conservation area or listed building then additional restrictions may apply.

Regardless of the type of heat pump, they all essentially transfer heat from one place, such as the air, ground or water, to another, such as to heat inside your home. They do this using electricity to power a compressor and evaporator, which is similar to a household refrigerator but in reverse. 

Heat pumps are a very efficient option for heating your home. You could expect around 250-300% efficiency from a typical air source heat pump, and 350-400% efficiency from a ground source heat pump! The exact efficiency will vary depending on the type, make and model of heat pump you choose, as well as the average temperature where you live, and how well insulated your home is. 

The Boiler Upgrade Scheme (BUS) is a government scheme offering grants of up to £7,500, to help homeowners with the cost of installing energy efficient, low-carbon heating systems such as heat pumps.