A lower heating bill does not necessarily mean a home became more efficient. The billing period may be shorter, the weather warmer, or the unit price lower. Start with those differences before attributing a change to a thermostat or a new window seal.
This guide provides a bill-comparison method, not a promised saving or a universal temperature prescription. The calculations below are invented examples. They are not measurements from a household or current utility prices.
1. Identify what the bill actually measures
Put two bills side by side and record the start and end dates, number of billed days, meter units, usage, unit rate and fixed charges. Check whether the meter reading was actual or estimated. An adjustment for an earlier estimated reading can distort a single month's comparison.
| Item | What to check | Why it matters |
|---|---|---|
| Gas | Is usage in volume units or an energy unit? | Copy the supplier's conversion rather than treating unlike units as equal |
| Electricity | Does the meter also cover appliances and hot water? | Total electricity use is not a direct measure of space heating |
| Shared building heat | How are individual use and shared charges allocated? | Some charges may not change when your own usage falls |
| Delivered fuel | Is this the amount bought or the amount consumed? | A delivery invoice alone may not describe that month's usage |
Use the rate and allocation rules on your own supplier's bill. If they are unclear, ask the supplier or building manager before trying to reproduce the total.
2. Work through a comparison without claiming a cause
Assume both bills use the same energy unit. For this simplified example only, ignore tax, tiered rates and adjustments.
| Item | Bill A | Bill B |
|---|---|---|
| Billed days | 30 | 28 |
| Usage | 900 units | 840 units |
| Usage per day | 900 ÷ 30 = 30 | 840 ÷ 28 = 30 |
| Unit price | 0.10 currency units | 0.12 currency units |
| Fixed charge | 10 | 10 |
| Calculated total | 900 × 0.10 + 10 = 100 | 840 × 0.12 + 10 = 110.80 |
Recorded consumption fell by 60 units, but daily use stayed the same and the bill rose by 10.80. Neither the smaller consumption total nor the larger bill proves that a heating adjustment worked or failed.
For a separate price comparison, applying Bill A's price to Bill B's usage gives 840 × 0.10 + 10 = 94. This isolates the rate difference in this simplified example; it still does not remove the effects of weather, occupancy or other appliances. Real tariffs may require separate calculations for each tier or time period.
3. Check the heating system before changing its schedule
Record the equipment model, current operating mode and any manufacturer instructions about scheduling, extended absence and freeze protection. Do not assume a setting copied from another home suits your equipment or occupants. If someone remains cold, restoring adequate warmth takes priority over the comparison.
ENERGY STAR notes that variable-capacity heat pumps may perform best with a manufacturer-recommended thermostat. Check compatibility before buying a replacement control. For building-managed heating, ask which settings you are actually allowed to change.
Change one controllable setting at a time and note the date, comfort and any unusual equipment behaviour. Do not use this article as a reason to disable protection settings, disconnect equipment during freezing weather or open fuel, electrical or pressurised components.
4. Inspect drafts without blocking necessary ventilation
Look for damaged seals around accessible windows and exterior doors. Record the location, photograph the defect for your own records, and check the window or door manufacturer's repair instructions. In a rental, ask the owner or manager which alterations are permitted before buying materials.
Air sealing must preserve necessary ventilation. The US Department of Energy explains that inadequate air supply can allow moisture and combustion gases to accumulate. Do not seal vents, flues or unknown openings. Refer work around combustion equipment and uncertain ventilation to a qualified professional.
This is a visual inspection, not a smoke or flame test. Do not dismantle outlets or heating equipment to hunt for drafts. A visible gap is a repair candidate, not evidence of a particular percentage saving.
5. Keep a comparison sheet and record uncertainty
Save the heating-bill comparison worksheet. It is a blank text file; fill it in on your own device without uploading bills or account details.
Record each bill's dates, days, units, consumption, daily use, price and fixed charges. Add changes in occupancy, weather and equipment settings. If your supplier provides weather-adjusted comparisons, read how it calculates them; do not assume that last year's same calendar month had identical heating needs.
A useful conclusion can be modest: “Daily use was lower, but this period was warmer, so I cannot attribute the difference to the new seal.” If a bill changes unexpectedly, check readings and tariff changes with the supplier. Use the fixed-cost review for contract comparisons rather than treating a lower advertised monthly price as a guaranteed saving.