How to Do a DIY Home Energy Audit

Collect 12 months of bills or meter readings for every fuel. A full year matters because heating, cooling and lighting change with the seasons.

• Electricity — kWh per month.
• Gas — kWh, or m³, cubic feet, MJ or therms. Convert to kWh with the gas to kWh converter, using the calorific value on your bill where stated.
• Oil, LPG, wood — delivered quantities and dates, with the energy content stated by your supplier.
• Tariff structure — unit rate, standing charge, and any time-of-use or tiered pricing. Standing charges do not change with use, so savings come only from the unit rate.

Plot the months. The shape shows the seasonal pattern; the total is your annual baseline.

Bills give totals; the next step is a rough split between space heating, water heating, cooling, appliances and lighting, and EV charging where relevant.

A useful first estimate for a fuel used for both heating and hot water is the summer method: months with no space heating approximate the year-round loads.

Illustrative: gas 13,500 kWh a year; summer months average 300 kWh each (hot water and cooking). Year-round loads: 300 × 12 = 3,600 kWh Space heating (estimate): 13,500 − 3,600 = 9,900 kWh

This is an approximation — hot-water use is often higher in winter — but it shows the order of magnitude. Do the same for electricity if you heat or cool with it. If an EV charges at home, a charger with its own meter separates that load directly.

Observation tells you what to investigate, not how many kWh it costs. Note what you find and where:

• Insulation — visible loft insulation depth and gaps, especially around hatches. Do not disturb insulation you cannot identify, and take care in lofts (joists, wiring).
• Windows and doors — draughts you can feel, worn seals, condensation between panes.
• Air leakage indicators — draughts at skirting boards, service entries, letterboxes and unused chimneys; cold spots and recurring condensation or mould.
• Heating distribution — radiators that are cold at the top or slow to heat, uninsulated pipes in unheated spaces.
• Controls — what the thermostat, timer and radiator valves are set to, and whether heating runs when rooms are empty.
• Hot-water system — cylinder insulation and the temperature setting. Do not lower stored hot water below what the manufacturer and local health guidance require for Legionella control.

• Smart meter or in-home display — half-hourly or hourly readings show when energy is used. The overnight minimum is your always-on load.
• Manual baseline — read the electricity meter late at night with nothing deliberately running, again an hour later; the difference is kWh per hour of always-on load.
• Plug-in energy monitor — kWh over a typical day or week for any plug-in device. More reliable than a rating label, which shows maximum power, not typical use.
• Appliance labels — an upper limit for devices you cannot plug in.
• Heating-system records — boiler or heat-pump service records, controller energy reports, and the heat pump's own meter if it has one.
• Fuel deliveries — dated quantities show seasonal use for oil, LPG or wood.

The Standby Power Audit adds up always-on devices; the Home Energy Audit Calculator turns appliance power and hours into annual kWh and cost.

List each possible change and score it on five things. A rough rank you can explain beats a precise-looking number you cannot.

A DIY audit is observation and measurement. These need a qualified professional:

• Electrical inspection — do not open consumer units, sockets or fixed wiring. Plug-in monitors and meter readings are the safe DIY tools.
• Combustion safety — gas, oil and solid-fuel appliances, flues and ventilation. If you suspect a problem, stop using the appliance and contact a registered engineer; fit and test carbon monoxide alarms.
• Refrigerant work — heat pumps and air conditioners are serviced by certified technicians.
• Building-envelope diagnosis — a blower-door test measures air leakage, thermal imaging can locate missing insulation inside walls, and moisture or structural problems need a surveyor. A room-by-room heat-loss calculation is the basis for sizing a heat pump.

Consider a professional assessment before major renovation or a heating-system change, and ask what the report will contain.

An audit tells you which bigger decisions are worth investigating, with your own baseline as the input:

• Replacing a boiler with a heat pump — use your heating kWh from Step 2 in the Heat Pump Savings Calculator.
• Rooftop solar — use your electricity baseline and daytime use in the Solar Payback Calculator.
• Charging an EV at home — check charger power against your driving with the Home Charger Sizing Tool.

Doing the no-cost changes first means later systems are sized for the demand that remains. The Home Energy hub collects the related tools, and the methodology page documents their formulas.