How Hearthline works.
What the model uses
The plan combines the property type, age, floor area, heating fuel, existing improvements, energy use, tariff, budget and priorities supplied by the user. If exact consumption is unavailable, Hearthline estimates it from the property and occupancy answers, then scales the result to the annual bill when one is provided.
| Input | Default source or approach | Review cycle |
|---|---|---|
| Electricity and gas rates | Ofgem GB direct-debit averages | Quarterly |
| Solar and heat-pump central costs | Energy Saving Trust published guidance | Six-monthly |
| Heat-pump grants | Ofgem and GOV.UK scheme pages | Quarterly and at policy changes |
| Measure savings | Published UK benchmarks, scaled to modelled energy spend | Six-monthly |
Why results are ranges
Installer prices, weather, occupancy, workmanship, moisture risk, orientation, shading and behaviour differ. Hearthline places a range around the central planning case and offers conservative, typical and optimistic saving scenarios. These are not confidence intervals or guarantees.
How measures are ordered
Measures begin with a base priority reflecting disruption, cost and building sequence. The ranking is then adjusted by the user’s priorities. Comfort gives more weight to fabric measures; bill savings favour controls, insulation and solar; carbon gives more weight to solar and clean heat. Commercial partner information is added only after this calculation.
Important limitations
- No postcode-level weather, roof geometry, orientation, shading or local labour pricing is modelled.
- Indicative EPC bands are deliberately not predicted; only an accredited assessment can establish an EPC rating.
- Historic, listed, solid-wall and damp-affected homes require specialist moisture and conservation advice.
- Heat-pump running costs depend on room-by-room heat loss, emitter sizing, flow temperature and achieved seasonal performance.
- Grant rules and tariffs change. Always check the linked official source before committing.
Commercial independence
Some outbound links may earn Hearthline a referral fee. Partners do not supply the ranking, saving model or editorial wording. Paid links are labelled before the user clicks. Read the affiliate disclosure.