A homeowner considering a renovation will sooner or later come across both terms: an energy audit and a thermographic inspection. And then comes the question: what should I book? Do I need both? Is one of them unnecessary?
The short answer: they are not alternatives, but different tools for different jobs. The longer answer follows.
What an energy audit does
An energy audit is a calculation-based method. An energy specialist (authorised by the Ministry of Industry and Trade, MPO) gathers data about the building - dimensions, the make-up of its structures, the heating system, heat recovery ventilation, solar gains - and feeds it into a calculation model. The output is:
- An Energy Performance Certificate (PENB) with an assigned energy class (A to G)
- An analysis of energy consumption across different categories (heating, water heating, ventilation, lighting)
- Options for measures, with calculated savings and payback periods
An audit is a paper-based analysis. It works with assumptions about the properties of materials and structures. If you have design documentation, it is more accurate. If you do not (as with older houses), the specialist has to estimate - and estimates can be wrong.
Output: figures, classes, charts, options. Easy to understand, but abstract.
What a thermographic inspection does
Thermal imaging is real-time visual diagnostics. A drone fitted with a thermal camera flies around the building and measures the surface temperature of the façade, roof and windows. The output is thermograms - colour images in which each colour corresponds to a temperature.
Thermal imaging shows:
- Exactly where a thermal bridge runs (you can see it in the image)
- Where the masonry is damp or where there is condensation
- Where there are gaps around windows or in the roof structure
- Where insulation is missing or damaged
Thermal imaging is physical reality, not a calculation. It does not estimate - it measures what genuinely exists on the façade at that moment.
Output: thermograms, photo documentation, a description of the problems found. Visual, concrete, precisely located.
Where each method has its limits
Limits of an energy audit
- The quality of the output depends on the quality of the input data. Without documentation, it comes down to estimates.
- It does not show the location of problems. An audit will say “thermal bridges account for X% of losses”, but it will not say exactly where they are.
- It cannot detect moisture. The calculations assume the structures are dry.
- Hidden defects are beyond its reach. If the insulation is damaged but this is not visible from outside, an audit will not pick it up.
Limits of thermal imaging
- It does not calculate consumption or savings. Thermal imaging does not replace a PENB for NZÚ purposes.
- It needs a temperature gradient. Summer is unsuitable for façade inspections; the minimum is a 10°C interior/exterior difference.
- Interpretation requires expertise. An image on its own does not explain the cause; without context it can be misleading.
- It does not cover the interior. Internal surfaces can be measured with a handheld thermal camera, but a drone does not do this.
Why combining the two is ideal
An energy specialist who receives a thermographic report as supporting material works from a different starting point:
- More precise identification of problems - they do not have to guess where the thermal bridges are; they know it from the thermograms.
- A better choice of measures - if the masonry is damp, insulating over it without first addressing the moisture would be a mistake; thermal imaging reveals this.
- A shorter site visit - the thermograms cover the façade, so the specialist can focus on the interior and the building’s systems.
- A more credible result - a calculation model anchored in physically verified data is more accurate.
For you as the owner, this means: fewer guesses, a more precise renovation plan, and a better chance that the actual savings match what was promised.
Practical scenarios: what to book, and when
Scenario 1: You are planning to apply for NZÚ Light
You need a renovation passport → that requires an energy audit → thermal imaging improves it and can make it cheaper. Book the thermal imaging first.
Scenario 2: You have a specific problem (draughts, mould, a high bill)
Thermal imaging is the first step. It quickly locates the cause. If it turns out the problem is systemic, only then does an energy audit make sense, for a comprehensive solution.
Scenario 3: You are buying an older house
Thermal imaging is ideal due diligence - in under an hour it reveals hidden risks (damp, water ingress, poor insulation). An energy audit then helps price the cost of renovation.
Scenario 4: An owners’ association is planning to insulate an apartment building
Both tools are needed. Thermal imaging for a precise brief to the insulation contractor and for a follow-up inspection after completion. An energy audit for the grant documentation and the members’ meeting decision.
The takeaway
Thermal imaging and an energy audit are not competitors. They are tools for different phases of the process:
- Thermal imaging = diagnosis - what the problem is, and where
- Energy audit = the plan - how to solve the problem, and how much it will save
If you only have the budget for one and want an immediate benefit: book thermal imaging. If you want a grant: you will need both, and thermal imaging should come first.
Interested in a thermographic inspection? Send us your enquiry - we reply within 24 hours with a price and an available date.