How a Home Energy Audit Works

Most homes waste some of the energy that goes into heating, cooling and running them. The trouble is that the waste is usually invisible: warm air slipping out through gaps around a loft hatch, cold air seeping under doors, an ageing furnace running harder than it should. A home energy audit is a structured way of finding those losses so you can decide which improvements are worth making.

What an audit is

A home energy audit, sometimes called an energy assessment, is an evaluation of how a house uses energy and where it loses it. A professional audit typically takes a few hours and ends with a report that lists problems and recommends fixes, often in order of priority. Some utilities and local programmes offer audits at a reduced cost or free of charge, so it is worth checking what is available in your area.

There is also the do-it-yourself version: a walk-through using simple tools and careful observation. It will not be as thorough, but it can catch many common issues.

What a professional assessor looks at

The building envelope

The envelope is everything that separates the inside of your home from the outside: walls, roof, floors, windows and doors. The assessor checks how well it keeps conditioned air in and outdoor air out. That includes looking at insulation levels in the loft or attic, walls and floors, and identifying gaps where air leaks through.

Heating and cooling systems

Boilers, furnaces, heat pumps and air conditioners are inspected for age, condition and efficiency. The assessor may look at filters, ductwork, pipe insulation and thermostat settings. Leaky ducts running through unheated spaces are a common source of lost energy.

Water heating

The water heater’s type, age, insulation and temperature setting are reviewed, along with whether hot water pipes are insulated.

Lighting and appliances

Some audits include a look at lighting and major appliances, noting older equipment that uses more electricity than modern alternatives.

Ventilation and moisture

Sealing a house tightly saves energy, but a home still needs fresh air. A good assessor considers ventilation and signs of moisture problems so that recommendations do not create new issues like condensation or poor indoor air quality.

The tools involved

Two tools are particularly common in professional audits.

Blower door test. A powerful fan is mounted in an exterior door frame and used to lower the air pressure inside the house. Outside air then rushes in through every gap and crack, making leaks easier to find and allowing the assessor to measure how airtight the home is overall.

Thermal imaging camera. An infrared camera shows temperature differences across surfaces. Areas of missing insulation or air leaks appear as distinct colours on the screen, revealing problems hidden inside walls and ceilings.

Assessors may also use tools to check combustion safety on gas appliances, measure duct leakage or log electricity use.

Preparing for an audit

A little preparation helps the visit go smoothly:

1. Gather recent energy bills so the assessor can see your usage patterns across the year.
2. Make a note of any problem areas, such as cold rooms, draughts or condensation.
3. Ensure access to the loft or attic, basement, crawl spaces and the heating system.
4. Close windows and set the thermostat as you normally would.
5. Have questions ready about specific upgrades you are considering.

Doing a basic audit yourself

If a professional audit is not an option right now, you can still learn a lot on your own.

• Hunt for draughts. On a windy day, move a hand or a lit incense stick slowly around window frames, door frames, electrical outlets on exterior walls, loft hatches and places where pipes enter the house. Flickering smoke points to a leak.
• Check insulation. Look in the loft or attic to see how deep the insulation is and whether it covers the whole area evenly.
• Inspect windows and doors. Look for worn weatherstripping, cracked seals and gaps you can see light through.
• Review the heating system. Note its age and when it was last serviced. Check and replace filters as needed.
• Look at your bills. Big seasonal spikes can show where most of your energy goes.

Reading the results

An audit report often groups recommendations by cost and impact. Typical findings include sealing air leaks, adding insulation, insulating ducts and pipes, servicing or replacing heating equipment, adjusting thermostat and water heater settings, and upgrading lighting.

Air sealing and insulation are frequently among the most effective improvements, because they reduce the amount of heating and cooling the house needs in the first place. Upgrading equipment usually comes later and makes more sense once the envelope is in better shape, since a tighter home may need a smaller system.

Deciding what to do first

Not every recommendation needs to happen at once. A practical order is often:

1. Low-cost fixes you can do yourself, such as weatherstripping and draught excluders.
2. Air sealing and insulation, which often bring noticeable comfort improvements.
3. Servicing existing equipment so it runs as efficiently as possible.
4. Larger investments, such as replacing windows or heating systems, planned around their remaining lifespan.

Beyond lower bills

The benefits of an audit are not only financial. Fixing draughts and adding insulation tends to make rooms more evenly comfortable, reduce noise from outside and help heating and cooling systems last longer. For many households, the improved comfort is what they notice first.