Your energy bill can tell you what the household bought, but it may not tell you how much energy the underfloor heating used. This is especially true where one boiler or heat pump also supplies hot water, radiators or other loads.
Start with the correct units
Electricity is normally billed in kilowatt-hours (kWh). Gas suppliers convert meter volume readings to billed energy. The billed energy component is the number of kWh multiplied by the applicable unit rate. Standing charges and other bill adjustments are separate.
Use the actual billing dates, actual or estimated readings, registers, applicable tariff rates and standing charges—not only the amount collected by Direct Debit.
Simple energy-cost arithmetic
Suppose a fictional UK household bill covers 28 days and reports 840 kWh of gas at a fictional rate of 6.2 p/kWh:
- Energy charge: 840 × £0.062 = £52.08.
- Fictional standing charge: 28 × £0.31 = £8.68.
- Illustrative amount before other adjustments: £60.76.
The arithmetic is correct for these constructed figures, but £60.76 is not a measurement of underfloor-heating cost if the same gas supply is used for hot water or radiators.
A separately metered electric bathroom mat using 24 kWh at an illustrative 25 p/kWh would have a measured energy component of £6.00 for that period. Do not count a household standing charge twice when estimating incremental energy use.
These are examples from the book, not current tariff quotes or predicted savings.
Electric UFH versus water-based UFH
Electric mats or cables turn purchased electricity into heat at the floor, subject to the controls and actual installed duty. A separate meter can sometimes establish energy use for that zone.
Wet underfloor heating distributes heat made elsewhere. Its cost depends on what supplies it—gas boiler, heat pump or another source—and how the home is controlled and insulated. The floor itself is an emitter, not a fuel.
A heat pump’s electrical input is not the same as heat delivered, and a single displayed efficiency number does not reliably allocate heat to a particular floor zone. You need appropriate metering and interpretation before claiming a zone-specific cost.
Five steps to investigate a higher bill
- Align the billing periods and compare their lengths.
- Check measured versus estimated readings and any corrections.
- Compare kWh and unit rates separately from standing charges, credit or monthly payments.
- Record colder weather, occupancy, hot-water use and any changed schedules or flooring.
- State explicitly what cannot be separated: ‘underfloor heating share unknown’ is better than a guessed allocation.
A January bill and a September bill are not controlled experiments. If a boiler also heats radiators and water, the extra cost cannot simply be assigned to the floor.
What does a useful schedule comparison establish?
A permitted schedule adjustment might improve the time a room becomes comfortable, but that does not automatically prove lower bills. Even with observed kWh differences, outdoor temperature, tariff slots and other loads can confuse the comparison.
Read whether underfloor heating should stay on all the time before changing a programme. For persistent discomfort see the safe first checks.
Living With Underfloor Heating contains the full fictional worked calculations, an Energy and Comfort Comparison Sheet and notes on when professional energy monitoring is required.