Conducting a Home Energy Audit: NZ Guide

A home energy check can help identify insulation, draught, heating, hot-water and lighting issues. Costs, savings and payback remain property- and household-specific.

EECA provides an online healthy-home check, or a certified adviser can visit, assess the home and tailor an improvement plan. Confirm the scope, tools, qualifications and any fee with the provider.

Starting with Your Power Bills

Before inspecting your home, review your electricity bills from the past year. Look for patterns in your consumption. Do your bills spike in winter? How does your usage compare to similar households? Most electricity retailers provide usage data and comparisons online.

• What is your average daily consumption in summer versus winter?
• Has your usage increased significantly over recent years?
• Are you on the best plan and tariff for your usage pattern?
• Do you have any appliances on continuous high consumption?

Understanding your baseline consumption helps you measure the impact of any improvements you make. It also highlights obvious anomalies worth investigating.

Checking Insulation

Insulation is the foundation of an energy-efficient home. Heat rises, making ceiling insulation particularly important. Ceiling insulation is often an accessible and effective place to start, but the heat-loss share varies by building.

If you can access your roof space safely, check what insulation is present. Look at the depth and condition. Old insulation may have settled, compressed, or been disturbed by electrical or plumbing work, leaving gaps. New-building insulation requirements vary by climate zone and construction. For an existing ceiling, EECA recommends checking coverage, condition and whether insulation is less than 120 mm thick or below the joists.

Underfloor insulation is harder to inspect but equally important for homes with suspended timber floors. A cold floor can have several causes. Where access is safe, check whether underfloor insulation is present, clean, dry, suitable and still correctly fitted, or use a qualified assessor.

Wall insulation is the most difficult to assess without invasive testing. Wall insulation cannot be inferred reliably from age alone. EECA recommends using the opportunity to have an expert check the wall cavity when cladding or internal linings are opened; retrofit work typically requires building consent.

Finding Draughts and Air Leaks

Draughts are one of the easiest problems to identify and among the cheapest to fix. On a cold, windy day, walk through your home and feel for air movement around windows, doors, and other openings.

• Around window and door frames
• Under external doors
• Through unused fireplaces and flues
• Around pet doors
• Through gaps in floorboards
• Around pipes and cables penetrating walls
• Through exhaust fans and rangehoods

Check for visible gaps and feel for air movement around openings on a cold, windy day. Avoid open-flame tests, and choose products that do not obstruct required ventilation or appliance safety.

Assessing Windows and Glazing

Windows are the weakest point in most homes' thermal envelope. Single-glazed windows, standard in homes built before the 2000s, have R-values around 0.15, which is dramatically lower than even minimal wall insulation.

Double glazing significantly improves performance, with R-values around 0.3 to 0.4 for standard units. Thermally broken frames and low-E coatings push this higher. Window upgrades can improve an otherwise well-insulated home, but the appropriate option, cost and benefit depend on the existing windows and the rest of the thermal envelope.

Short of full replacement, secondary glazing systems can improve single-glazed windows at lower cost. Heavy curtains with pelmets also help, provided they are properly fitted and closed at night.

Evaluating Heating Systems

How you heat your home affects both your comfort and your power bills. Different heating systems vary enormously in their efficiency and running costs.

Heat pumps are generally the most efficient option, producing three to four units of heat for every unit of electricity consumed. Modern inverter units maintain stable temperatures efficiently. Older non-inverter units or those sized incorrectly for the space will perform less well.

Electric heaters (fan, oil column, panel) produce one unit of heat for every unit of electricity, making them less efficient than heat pumps. They are suitable for occasional use but expensive as primary heating.

Wood-burner costs and performance depend on the appliance, fuel, operation and local clean-air and consent rules; check the current requirements before choosing or replacing one.

Clean heat pump filters monthly during heating season for optimal performance. Ensure heaters are correctly sized for the room; an undersized unit will run constantly without adequately heating the space, while an oversized unit cycles inefficiently.

Checking Hot Water

Hot water typically accounts for 25% to 30% of household energy use. Assess your hot water system's efficiency as part of your audit.

If you have an electric hot water cylinder, check the thermostat setting. EECA says stored hot water should be at least 60°C at the cylinder to prevent legionella growth and no more than 55°C at the tap to reduce burn risk. Wrapping your cylinder in an insulation blanket can reduce standing heat losses, particularly for older or poorly insulated units.

EECA says a hot-water heat pump uses around a third of the energy of electric-resistance or gas water heating, but suitability, installation cost and household savings must be checked for the property.

Auditing Appliances and Lighting

Walk through your home and list your major appliances. Note their age and energy rating if visible. Older refrigerators, freezers, and dryers are often significant energy consumers. An older or second refrigerator may add material energy use; measure it where possible and compare current energy-rating information before deciding whether to replace it.

Check for standby power consumption. Standby use varies by device and household; a plug-in power meter or retailer usage data can help identify persistent loads. Smart power strips and simple habits like switching off at the wall can eliminate this waste.

Lighting is another area worth examining. LED bulbs use roughly 80% less energy than incandescent bulbs and last far longer. If you still have incandescent or halogen bulbs, replacing them with LEDs is one of the simplest and most cost-effective efficiency improvements.

Professional Energy Assessments

While a DIY audit provides valuable insights, a professional assessment goes deeper. Certified home energy assessors use thermal imaging cameras to reveal heat loss invisible to the naked eye. They can identify insulation gaps, thermal bridging, and moisture problems you would otherwise miss.

Ask what the assessment and report include. Any costs, savings or priorities should be treated as estimates based on the home, household and proposed work.

Prioritising Improvements

Once you have completed your audit, prioritise improvements based on cost-effectiveness rather than total savings. Draught-stopping might save less than double glazing in absolute terms, but it costs a fraction of the price and delivers a far faster payback.

There is no universal priority order. EECA says a healthy-home check should consider insulation and heat retention, ventilation, heating, hot water and lighting; sequence work using the property assessment, safety, comfort, eligibility, quotes and estimated savings.

An energy audit is not a one-time exercise. As you make improvements, your next priorities change. Revisiting your assessment periodically ensures you continue to identify opportunities and track your progress toward a more efficient home.