Heat delivered is different from electricity consumed
A heat pump moves heat rather than producing all useful heat through electrical resistance. Its output-to-input ratio depends on the installation and operating conditions. For an annual estimate, use a suitable seasonal figure from the proposed design or measured system; one favourable laboratory operating point is not an annual result. Record whether auxiliary resistance heating, hot water and distribution losses are included.
Calculate energy charges
Under a simple model, electricity used = useful heat demand ÷ seasonal performance factor. Energy charge = electricity used × the unit tariff. A gas comparator uses heat demand ÷ seasonal efficiency × gas unit tariff. The form calculates only these energy components locally. It does not send the entered values to a quotation service.
Without JavaScript, the formulas and example below remain available. Use the same useful-heat boundary and currency for both options. Keep standing charges, installation, finance, service and replacement costs in separate rows.
Worked example and sensitivity
For a fictional annual heat demand of 12,000 kWh, seasonal performance factor 3 and electricity tariff 0.25 currency units/kWh, the energy charge is 12,000 ÷ 3 × 0.25 = 1,000 units. A fictional gas system at 90% efficiency and 0.08/kWh costs approximately 1,066.67 units in gas energy. The difference is about 66.67 units under these assumptions, before the omitted costs.
Change the performance factor to 2 and the heat-pump energy charge becomes 1,500. That one change reverses the comparison. It illustrates why a generic saving percentage cannot substitute for your design and tariff. The defaults are fictional, not present market rates or a supplier’s promised performance.
Questions for a site-specific quote
| Ask for | Why it matters |
|---|---|
| Heat-loss calculation and design temperature | A capacity label alone does not establish comfort in the building |
| Proposed emitters and water temperature | Identify changes to radiators, ducts or controls |
| Seasonal assumptions and backup heat | Understand which electricity demand the estimate includes |
| Electrical and installation work | Keep necessary works in the capital budget |
| Service, noise and commissioning | Ask how the completed installation will be checked |
We did not inspect your building or test a product. Confirm a site-specific design and current tariff before making a purchase decision. The worksheet is useful for checking the arithmetic in a quote, not replacing that design.
Sources and scope
- IEA, The Future of Heat Pumps: how a heat pump works (2022; link rechecked 11 October 2026) — Explains the heat-transfer mechanism; not certification of the seasonal efficiency or cost of a reader’s installation.
Sources checked October 10, 2026. AI-assisted research and drafting. The examples, calculations and worksheets are Luminesca editorial work; they are not measured trials, first-hand reporting or an independent certification. Universal savings, equipment performance and payback claims have been removed. The replacement provides a transparent calculation rather than a product recommendation. Report a specific correction with its source.