Home Insulation Comparison Calculator

What This Calculator Compares

Compare 6 types of insulation work using the cost and useful heat saving you expect for your own property. The initial numbers are illustrative scenarios for learning the arithmetic, not surveyed UK price ranges. Replace them with written quotes and an assessor’s energy estimate before making a spending decision. A flat may have neither its own loft nor an exposed ground floor; both start excluded when you select Flat. A solid concrete floor is outside this suspended-floor comparison.

How the Cost and Saving Estimates Are Calculated

Annual purchased fuel saved equals useful heat saved divided by heating efficiency. For example, 900kWh of useful heat at 90% efficiency saves 1,000kWh of gas. At 7.33p/kWh that is £73.30 per year; a £1,000 job then takes 13.6 years to repay its cost. Resistance electric heating uses a 100% assumption. Heat pumps need a different model using seasonal performance and are outside scope. Storage heaters need the tariff for the electricity actually displaced, not necessarily the all-day rate.

The starting tariffs are Ofgem’s GB Direct Debit averages for 1 July–30 September 2026: 7.33p gas and 26.11p electricity. They include VAT. Standing charges are unchanged by insulation, so they are excluded. Each fuel retains its own edited tariff when you switch.

Why Starting Loft Depth Matters

Adding insulation to an empty loft is different from topping up an existing layer. Energy Saving Trust quotes £750 for 0mm to 270mm and £600 for 120mm to 270mm in Great Britain, with a £17 annual GB saving for that top-up example. These dated reference examples are context, not the defaults used here. This tool’s deliberately editable loft scenarios use 1,850kWh useful heat for none, 925kWh for under 100mm, and 277.5kWh for 100–269mm. They are modelling assumptions, not measured savings or interpolation of EST data. At 270mm or more the example excludes further top-up; ask an assessor about your actual condition and material.

Funding: Check Current Availability

The Great British Insulation Scheme ended on 31 March 2026. Government’s ECO4 decision extends ECO4 until 31 December 2026 for existing obligations and remediation; it does not guarantee that suppliers are accepting new applications. Ask your council or supplier about current routes, including Warm Homes support where available. No grant is assumed in these totals. If you have a confirmed grant, enter your remaining installed cost and retain evidence of what the grant covers.

Common Mistakes When Comparing Quotes

Get 2–3 written quotes covering the same area, preparation, access, ventilation, making good and VAT. A £1,000 headline price excluding scaffolding is not comparable with an all-in £2,000 quote. Do not select solid-wall work until the construction is confirmed: “Not sure” excludes wall costs and savings here. Internal and external insulation are normally alternatives, so totals include internal only when both are offered; the table still shows both options. Savings from several measures can overlap. A sum is a scenario, not a whole-home energy assessment.

What Happens After You Compare

Use the fastest-payback result to choose questions for an installer, not to authorise work. Verify qualifications, insurance and references, and get an assessment of damp, ventilation and fire requirements. Ask separately about regulatory sign-off and any product or workmanship guarantee: a CIGA guarantee is not itself building-control approval. Keep at least 2 comparable quotations, the assumed annual kWh reduction and the tariff used with your copied results. Comfort, disruption, material lifetime and necessary repairs may matter more than the shortest numerical payback.