Before replacing equipment or adding solar, a home energy audit can show where your home wastes energy. Many utilities offer subsidised audits.
Key Takeaways
- Audits assess insulation, air leakage, heating and cooling equipment and appliances.
- Blower door tests measure how leaky a home is and help find leaks.
- Air sealing and insulation are often the most cost-effective upgrades.
- Use audit results to prioritise improvements.
What happens during an audit
- Visual inspection of insulation, windows and doors
- Blower door testing
- Infrared imaging
- Equipment checks
Blower door tests
A powerful fan depressurises the house to measure air leakage.
Common findings
- Attic air leaks
- Insufficient insulation
- Duct leaks
- Old equipment
Prioritising upgrades
- Air sealing
- Insulation
- Duct sealing
- Equipment upgrades
What the blower door numbers mean
A blower door test reports air leakage, commonly as ACH50 — air changes per hour at a pressure difference of 50 pascals. In plain terms, it estimates how many times the air in the house would be replaced each hour under test pressure. Older, leaky homes can have high ACH50 values; newer homes built to tighter codes are lower. The auditor can compare your result with typical values for homes of your age and climate and re-test after air sealing to measure improvement.
While the house is depressurised, auditors often walk around with smoke pencils or infrared cameras to find specific leaks.
Where the biggest leaks usually hide
- Attic floor penetrations: gaps around plumbing vents, wiring holes, recessed lights and chimneys
- Attic hatches and pull-down stairs without weatherstripping or insulation
- Rim joists in basements, where the house frame sits on the foundation
- Duct connections in unconditioned attics and crawl spaces
- Fireplace dampers
- Gaps around windows and doors
Sealing these with caulk, foam and weatherstripping is often inexpensive relative to the savings and comfort improvement.
Why order matters
Auditors usually recommend sealing air leaks before adding insulation. Insulation slows heat transfer, but air moving through gaps carries heat around it. Sealing the attic floor before adding attic insulation makes both more effective.
Reducing heating and cooling loads first also means that when you replace equipment — for example, with a heat pump — you may be able to install a smaller, less expensive system.
Health and safety checks
Good audits include combustion safety testing for gas appliances, especially after air sealing, because tighter homes can affect how furnaces and water heaters vent. Auditors may also check for carbon monoxide and recommend ventilation improvements such as bathroom fans that vent outdoors.
Reading the report
A useful audit report should include:
- Test results before work
- A prioritised list of improvements with estimated costs
- Expected energy savings
- Safety notes
- Information about available rebates
Frequently Asked Questions
How long does an audit take? Often a few hours.
Are audits expensive? Many utilities subsidise them.
Can I do a DIY audit? Basic checks are possible.
Do audits include recommendations? Yes, typically.
The bottom line
An energy audit shows where to start, often with low-cost air sealing and insulation.
