Important update: Please note the Home Energy Model (HEM) is currently in development and this is NOT a live version of HEM. It should not be used to inform decisions by those choosing to access it.

The consultation tool gives you the opportunity to interact with the model and understand whether different dwelling designs are likely to comply with the proposed Scottish Homes Standard. Please read the User Guide to find further information on how to use the consultation tool.

This consultation version of the tool is provided for the purposes of the Scottish Government’s Scottish Homes Standard consultation only, and as such does not reflect any changes which may be made in the light of consultation responses. In addition, at the time of publication, the UK Government response to the Home Energy Model Consultation has not been published and the HEM may be subject to change following consideration of the responses. You can see the latest release of the Python code not linked to the consultation tool here.

The Home Energy Model represents a complete overhaul compared with SAP 10.2 and previous versions of SAP. The consultation document linked above, explains the key changes, and we would encourage you to read the consultation. However, this consultation tool looks similar to previous versions of iSAP and its user interface is very basic. Please note that this is not representative of the user experience users will have when the final version is planned to be released in 2026. This tool has only been developed for the purpose of providing users with a basic working tool.

Limitations of HEM

HEM is still in development by the UK Government, therefore desired features may be missing, and areas may be subject to change. Below is an inexhaustive summary of key areas of risk associated with the use of HEM, focusing on areas of current underdevelopment within the methodology:

Products Characteristics Database (PCDB): The UK Government are developing a PCDB database which is compatible with HEM, however, certain product types have not yet been ported onto the HEM compatible database, including: Boilers, FGHRS, WWHRS, Storage heaters, Heat networks and heat interface units. For those product types which have been ported, the full set of products in the PCDB has not been translated and a set of ‘dummy’ products has been created to allow use of the HEM database for testing.

Technologies: Several technologies have yet to be implemented in full in HEM, these include: Cooker boilers, Solid fuel boilers, FGHRS, heat interface units, chimneys and cowls, combustion appliances (fireplaces, gas fires).

Fuel types: Not all fuel types compatible with SAP are compatible with HEM. The dummy PCDB products only use gas or electricity the full set of compatible fuels are: MAINS GAS, ELECTRICITY, CUSTOM, LPG BULK, LPG BOTTLED, LPG CONDITION 11F.

Variable grid profiles: The Scottish Homes Standard wrapper matches the 2023 Future Homes Standard consultation fuel factors. However, there is an option available to instead test the impact of using variable grid profiles, which will utilise the demonstration variable grid profiles and tariff file developed to date by UK Government. However, please note that these variable grid profiles are not to be considered final due to limitations of the grid dataset and may lead to unrealistic outcomes. For example, it may be that there are periods where electricity is cheap in the cost file (perhaps because a lot of solar at that time) but the data used for the CO2 factors doesn’t match and suggests that emissions are high (perhaps because that data assumed a cloudy day). This disparity between data sets would result in cost-optimising smart technologies drawing more energy during that low-cost period and lead to apparently high CO2 emissions. Unfortunately, no documentation on the source of these datasets is available at the time of writing to guarantee compatibility of the two files.