The return on investment of an energy retrofit is calculated by dividing the net cost left after grants by the annual saving expected, never the total amount of the works. Orders of magnitude observed run from 3 to 5 years for loft insulation, 5 to 8 years for a heat pump and 10 to 15 years for external wall insulation. The calculation horizon is set on the service life of the measure, and the costing takes in the items forgotten at the quote, strip-out and disposal, scaffolding, making good finishes, connections and maintenance, plus a margin of 5 to 10% for site contingencies. Quoting a payback time without writing down the energy price assumption used exposes the firm to a challenge from the client's first bill.
Clarify ROI in energy renovation: what you need to measure in 2026
Distinguish total cost, payback time and net gain over the years
To manage your ROI, separate three concepts. The total cost includes the studies, the works, maintenance and above all the remaining cost after funding. Payback time answers a simple question: how many years it takes to get the money back.
Identify the items that weigh the most: heating, insulation, ventilation, hot water
Start by measuring what actually consumes energy before the works. In most homes, heating remains the main item, followed by hot water. Insulation acts like a coat: it durably lowers needs. Ventilation prevents humidity and protects the gains, especially after reinforced insulation.
Set your calculation horizon: 5, 10, 15 years depending on the type of project
In 2026, choose a horizon consistent with the equipment's lifespan. 5 years for a settings adjustment, a thermostat, a small heat pump. 10 years for a balanced package of works. 15 years for the envelope, walls, lofts, windows. Keep the price of energy in mind: it's what ultimately shapes the result. To go further, set up consumption monitoring after renovation to verify the savings actually achieved.
Cost the investment accurately: every cost to include
Include materials, labour, studies, and ancillary costs (removal, scaffolding, finishing work)
For an all-inclusive costing, add up materials, labour and studies. Also think of the ancillary costs that are often forgotten: removal and waste disposal, scaffolding rental, protection, drilling, patching and finishing touch-ups, electrical or hydraulic connections, compliance work and inspections.
Anticipate contingencies: safety margin, price variations, unforeseen site issues
On a job site, not everything is visible at first glance. Plan a safety margin (often 5 to 10%) for surprises: hidden moisture, degraded substrates, thermal bridges, difficult access. Also frame material price variations with a quote validity period and by tracking building cost indices.
Account for maintenance: upkeep, replacement, warranties
A good budget includes life after the works: upkeep (e.g. heating and ventilation equipment), small replacements (filters, circulators, control components), and warranties, perfect completion (1 year), biennial (2 years), decennial (10 years). This is what protects your real ROI and prevents an energy saving from turning into an unexpected bill.
Estimate energy savings credibly and usably
Start from a baseline: bills, usage, floor area, existing insulation quality
Before promising gains, establish a reliable picture of the existing situation. Gather 12 to 24 months of bills, the heated floor area, the setpoints, occupancy schedules, the type of ventilation, and what is already insulated (lofts, walls, floors, windows). If possible, also record the equipment's power ratings and ages.
- Bills in kWh and euros, summer and winter alike
- Main uses: heating, domestic hot water, cooking
- Visible weak points: air leaks, thermal bridges, humidity
Translate the gains into euros: kWh saved, energy price, cautious scenarios
Convert the kWh saved into euros using a cautious scenario. In 2026, tariffs may fluctuate. Offer at least two price assumptions (low and high) and state clearly what's included. You get an ROI that's readable, and above all comparable between solutions.
Check consistency with reality on site: settings, behaviour, commissioning
An estimate only holds if the installation follows through. Check ventilation airflow rates, heating-curve settings, balancing, and commissioning (heat pump, mechanical ventilation, controls). Also confirm the expected occupant habits: target temperature, airing, programming. Otherwise, the savings stay on paper only. To frame the checks to plan for, rely on these essential checks.
Calculate the ROI step by step: method, formulas and worked examples
Apply the useful formulas: ROI %, simple payback time, discounted payback time
Start by costing the project, then the annual savings. ROI formula: ROI % = (net gain / net investment) × 100. Simple payback time = net investment / annual savings. Example: €12 invested, €10 saved. Simple payback: 12 years. For the discounted payback, apply a rate (e.g. 3%), since €10 tomorrow is worth less than €10 today.
Factor the funding into the calculation: what the measures attract, and the remaining cost
Work from the remaining cost. Net investment = quote including VAT minus what the measures attract, based on the rules in force in 2026 and your client's situation. Keep a separate line for ancillary costs (connection, flushing, ventilation) to avoid an overstated ROI. Public grants, CEE bonuses and financing instalments are deducted from the costing to show the real remaining cost before signature.
Compare several solutions: insulation alone, heat pump, hybrid, phased renovation
Put 3 to 4 scenarios side by side: insulation, heat pump, hybrid, phased. Compare net cost, savings, maintenance, summer and winter comfort. Insulation often delivers more consistent gains. A heat pump depends more on settings and the price of electricity. Choose the scenario with the best controlled risk, not just the shortest payback.
Optimise the profitability of your projects: concrete levers to improve ROI
Target the right packages of works: prioritise the envelope before the system
For a solid ROI, start with the envelope: loft and wall insulation, thermal bridge treatment, airtightness, then suitably sized ventilation. A less "leaky" home lets you size a heat pump or boiler more accurately, with lower consumption, fewer callbacks, and better client satisfaction.
Reduce the remaining cost: structuring the funding, supporting documents, compliance
From the quote stage, secure the funding route, the zero VAT rate on energy-saving materials and any local scheme. Prepare the key documents: detailed quotes and invoices, technical data sheets, proof of registration in the right scope, completion dates, declared floor areas and performance figures. A clean file avoids come-backs, speeds up payments and protects your margin.
Highlight the indirect benefits: comfort, property value, fewer breakdowns
Don't just sell kWh. Sell lasting comfort: a more stable temperature in summer and winter alike, less humidity, fewer breakdowns thanks to a less strained system, and often a higher property value through a better energy rating. In 2026, these arguments make the difference when the budget is being discussed.
