Thermopy Guide
How to estimate home heating costs
Use consumption and tariff data to forecast monthly and annual heating bills.
Start with real usage
Your utility bill gives the best baseline: kWh, therms or liters consumed during heating season. Multiply by current tariff including standing charges where relevant.
Compare upgrade scenarios
Run the Basic Heating Calculator with current vs proposed system to quantify savings from insulation, thermostat changes or boiler replacement.
Degree-days and climate drive annual demand
Colder climates and longer heating seasons raise annual kWh even for identical homes. Degree-day or design-temperature data helps normalize estimates when you move house, change setpoint, or compare years with unusual weather.
Fuel unit prices and standing charges
Multiply seasonal consumption by your all-in unit rate, then add standing charges and VAT/taxes where they apply to heating. Switching fuels without updating both the unit price and fixed charges will skew any bill forecast.
Envelope effect on the bill
Insulation, airtightness and glazing cut the kWh you need before any plant upgrade. A leaky envelope makes every tariff and every boiler or heat pump look expensive — model fabric improvements alongside system changes.
Example bill from usage and tariff
If space heating uses 12,000 kWh/year at €0.12/kWh equivalent, fuel alone is about €1,440 before standing charges. Split that across winter months for cash-flow planning, and keep a 10–15% buffer for colder-than-average years.
Comparing heating systems fairly
Align comparisons on the same weather year, indoor setpoint and hot-water share. Convert gas m³, oil litres and heat-pump electricity into delivered heat using realistic efficiencies (AFUE, SCOP) so you compare comfort delivered, not raw meter units.
When to recalculate
Recalculate after tariff changes, insulation or window upgrades, thermostat schedule changes, or a boiler/heat-pump swap. Use the Basic Heating Calculator to refresh annual and monthly forecasts with your latest inputs.
Get exact numbers with our free calculator
Use your room data, climate and energy rates to generate actionable results in minutes.
Open calculatorFAQ
Why is my bill higher than the estimate?
Weather variation, thermostat settings and hot water share of consumption can increase real bills vs average-year models.
Which tariff should I use?
Use your all-in unit rate (energy + distribution + taxes) for the fuel you actually burn for space heating.
Can I budget monthly?
Yes — divide annual heating cost by 12 and add 10–15% buffer for cold months.
Do night setbacks always save money?
Often yes for poorly insulated homes with fast-response radiators. In very well-insulated or high-thermal-mass homes, deep setbacks can save less than expected — and heat pumps may prefer steadier setpoints. Test with your own degree-day and recovery assumptions.
Why can a heat pump bill still look high?
Electricity unit rates are usually higher than gas per kWh, so even a good COP leaves a visible bill. High flow temperatures, resistance backup and cold winters increase consumption — check SCOP assumptions and emitter sizing, not only the install quote.