Home Energy Efficiency FAQs

Frequently asked questions

How does HEET work?

HEET calculates the energy demand of your home using information on the size of your home, its construction, its age, and the type of heating and insulation installed. The calculations the tool uses are a 99.9% accurate replication of those used to produce an Energy Performance Certificate (EPC).


An EPC is produced by an accredited Domestic Energy Assessor (DEA) who surveys your home, taking measurements and recording details about the construction of the building. HEET works on a similar basis but relies on you entering the information required about your home and some further assumptions Energy Saving Trust make based on what you’ve told them.

What assumptions does HEET make about my home?

HEET will make assumptions about the size and shape of your home, the materials your home is made from, the efficiency and other details relating to your heating system as well as other more technical information about your property. 

Who is responsible for any actions taken based on recommendations by Energy Saving Trust?

The results from HEET are indicative of the energy performance of your home and what can potentially be done to improve it. You should always speak with a qualified professional before commencing on any changes to your home to confirm that a recommendation is suitable and would have a benefit.

How accurate is HEET?

HEET will on average produce a Standard Assessment Procedure (SAP) score within 5-6 SAP points of an EPC. The accuracy for your property will depend on the accuracy of your answers to the questions Energy Saving Trust ask, and how far from ‘typical’ your home is. A SAP Assessment measures CO2 emissions, energy costs and thermal performance of building elements.  Properties that are very old or of an unusual build are more likely to have a larger SAP difference compared to their EPC. 

Can HEET produce an EPC?

Although HEET gives results very similar to an EPC, it’s not an Energy Performance Certificate. The report from HEET cannot be used in place of an EPC. How do Energy Saving Trust calculate the measure costs?


Measure costs in HEET are calculated from two parts, a fixed cost and a variable cost.  The fixed cost remains a static value regardless of the details of your property, but the variable cost is tied to a specific part of your property. For example, wall insulation costs vary with the area of external wall to be insulated. This way, the measure costs Energy Saving Trust quote you are tailored to your own property. 

What are Energy Saving Trust’s measure costs based on?

Each measure cost is based on the most appropriate sources available to Energy Saving Trust and their own expertise. These sources include data from MCS, funding schemes for energy efficiency and renewable measures, up to date installer estimate data, and industry price guidance.

Will you share any of my data with TrustMark?

To make sure you meet our criteria for the Green Together Reward, we’ll share some of your data with TrustMark. This will only be your postcode and details of the home improvements you tell us about on your claim form – never any personal information such as your name or details of the mortgage you hold with us.

If you register for the Green Together Reward, you consent to us sharing data with TrustMark. Here’s TrustMark’s Privacy Policy

How often do Energy Saving Trust update the measure costs?

The measure costs in HEET are reviewed regularly and are typically updated at least once a year. 

What’s included in the measure costs?

All measure costs are designed to include typical labour and material costs. By typical, Energy Saving Trust mean their costs will not include the cost of any ancillary or remedial work which may be required for your particular property.

Energy Saving Trust’s costs do not include any additional labour or materials required to fix the state of the property to get it ready for a measure such as general repairs to the material fabric or to fix damp issues, or any remedial work required after installation should there be any snagging issues.

All measure costs also include VAT where appropriate. For many energy-efficiency measures the current VAT rate is 0%.

Why are the measure costs Energy Saving Trust quoted different to those that I’ve had from installers or on my EPC?

The costs presented in the tool are only intended as a guide and not a definitive quote for the work. Quotes from installers may be higher or lower than the costs provided by the tool. The final cost of work will be influenced by complexity of the work, materials required, geography and availability of installers in your area.  Energy Saving Trust recommend speaking with three installers or as many as you need to feel confident that the quotes you have been given are competitive before making a decision.

How do Energy Saving Trust calculate fuel costs?

HEET calculates the energy demand of your home including the energy needed for heating, for lighting and for appliances. Each of these energy demands is then multiplied by a fuel price for each of the fuels used.

How up to date are the fuel prices Energy Saving Trust use?

Energy Saving Trust constantly reviews the domestic energy market and resulting fuel prices typically paid by domestic consumers. Their fuel prices are intended to reflect the latest typical prices households are paying. Currently, this means gas and electricity prices set by the UK Government’s Energy Price Guarantee. Other fuel prices, including oil, LPG, wood fuel, are based on retail analysis. Energy Saving Trust endeavour to keep fuel prices used reflective of typical consumer bills up to date, updating as regularly as necessary to reflect the domestic energy market.

Are Energy Saving Trust’s electricity and gas prices based on the Price Guarantee or the Price Cap?

Their current fuel prices for electricity and mains gas are based on the Price Guarantee.

When the Price Guarantee ends, they will perform an analysis on what the typical electricity and mains gas tariffs might be. If the energy market continues to be unstable and prices continue to be high, those tariffs would likely be based on the Price Cap. Should the energy market return to being a competitive energy market, their electricity and mains gas prices would be based on their own analysis of the available prices using data sourced from Ofgem and the UK Government.

Note that the Price Guarantee and Price Cap only cover electricity and mains gas. Energy Saving Trust’s other fuel prices, such as for LPG, oil and coal, are sourced from their own analysis of fuel prices currently available on the market.

What are Energy Saving Trust’s current fuel prices?

You can find their current fuel prices and the date they were last updated here.

How do Energy Saving Trust calculate carbon emissions and carbon savings?

HEET calculates the energy demand of your home including the energy needed for heating, for lighting and for appliances. Each of these energy demands is then multiplied by a carbon factor for each of the fuels used.

What are Energy Saving Trust’s latest carbon factors?

You can find a copy of the latest carbon factors here
You can also find more information on specific energy efficiency or renewable measures on the Energy Saving Trust website.
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