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BGS & HLC Reports

What is a HLC – and why is it important?

At Groundtherm we offer a comprehensive and holistic service – which means that we take care of your project from start to finish. Two crucial elements of the process are Heat Loss Calculations and British Geological Surveys.

‘HLC’ stands for Heat Loss Calculation. This must be carried out on your building before any other work commences, as it determines how much energy is needed to heat your property. Based on that fact we know what’s required in order for your ground source heating system to run successfully, productively and efficiently. In basic terms, we need to know exactly how much energy we need to get out of the ground to support the building – and a Heat Loss Calculation enables us to determine that.

Carrying out an accurate calculation of a building is complex and involves a variety of different factors. It isn’t just based on the design of your property alone – and it takes into account the make-up, insulation and fabric of the building. It’s these things that really influence the amount of energy needed to heat your property – not necessarily age or size. Once we’ve identified the fabric based on what we call ‘U values’, we then work out the heat loss.

The Heat Loss Calculation in essence indicates the size of pump needed to heat your property, and indicates how many Kilowatt Hours (energy) we need to heat the building and ensure a plentiful flow of hot water. We need to be certain of this before we begin to turn our attention to drilling down as the calculation tells us how much we need to take out and how deeply we need to excavate.


To tell if BGS and HLC Reports are right for you, there are a few key questions to consider:

Combined Shape

What is a BGS and why do I need it?

‘BGS’ stands for British Geological Survey. This is a calculation carried out using conductivity based on thermal geology. We need to know and understand the thermal geology of the earth beneath and surrounding your property in order to put together a system that is going to work efficiently for you. The BGS gives us a clear indication of the geology, the fabric of what’s actually in the ground. Using this alongside the Heat Loss Calculation, we’re then able to conclude exactly what is required to ensure that your system will work effectively for you.

Combined Shape

What is a SAP report?

SAP is a legal requirement, a type of building regulations report carried out by an architect which gives us an accurate picture of the fabric of a building - what a property is made and comprised of. SAP coordinates everything together and will be different (and therefore producing different results) depending on location and several geographical factors. We work out the ‘U values’ mentioned above based on a SAP report; so essentially the HLC itself is based on the SAP report. This makes it an essential aspect of the preparatory process.

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