How to use a thermal camera to cut energy bills

It's that time of year again - energy prices are rising, temperatures are falling, and we're wavering between donning another sweater or turning on the heating.

One way to stay warm while keeping your heating bills down is to keep more of the heat you generate inside your home - but first, you need to find out where it is escaping. 

Some of this will be obvious: uninsulated walls and lofts, and single-glazed windows are major culprits. But what about the hidden insulation gaps, air leaks and other thermal defects that cause draughty, chilly rooms?

Many of these can be fixed with a spot of simple DIY, if you know where to look. 

You might be surprised by the weak spots leaking heat around your home. That's where thermal imaging can help.

Read more: For quick fixes head to our guide to draught proofing your home or, if you're ready for a bigger project, check out our home energy efficiency guides.

What is thermal imaging?

A thermal camera is a device that ‘sees’ heat. Thermal imaging (or thermography) works by detecting infra-red radiation, which is invisible to the human eye.

Objects emit different amounts of infra-red radiation according to their temperature. A thermal camera converts the intensity of radiation to a visible image (or thermogram) in which each pixel records a temperature that is assigned a colour.

When pointed at your home, the camera detects the infra-red radiation emitted by the walls, windows, and roof and uses it to display a visual map of the surface temperatures.

To see a clear distinction between warmer and cooler surfaces, there should be a minimum difference of around ten degrees between the inside of your home and the outside air. Thermal surveys are best done when the outside temperature is below 10°C and your home is heated to around 19-20°C.

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How is thermal imaging useful?

Thermal imaging can help you spot thermal defects – the places where heat leaks out of your property. It’s especially helpful for pinpointing heat leaks that are hard to find in any other way, such as draughts through gaps and cracks that are hidden from view; patchy or missing insulation inside lofts and cavity walls; and missing or broken seals around doors, windows, loft hatches or other openings.

Thermal cameras can’t see through walls – the image is not an X-ray – but they can detect temperature differences on the surface of a wall caused by something behind the surface, such as damp or rodents.

What does heat loss look like?

A thermal survey covers both the inside and outside your home to identify areas where heat is leaking out.

From the inside, these areas will appear as cold spots; from the outside, you’ll see hot spots. 

The warmest areas will generally appear as brighter, red/orange colours, with the colder areas in darker or blue shades. However, most cameras have a range of settings, including different colour schemes, so make sure you know what the colours mean when looking at your images.

In the image below, showing the outside of a typical house, there are significant red areas on the wall, porch and bay, suggesting a lack of insulation there.

If walls are uninsulated, you’d expect them to lose heat, but they are likely to be an even temperature across most of the surface.

If you have solid or cavity wall insulation, there should be much less heat loss. Patches or hot spots in the image could indicate possible gaps, poor installation or failure of the insulation, which should be investigated and rectified.

It’s common to find problems at junctions between structural elements, around windows and doors, and at the eaves and skirtings due to gaps, thermal bridging or poorly installed insulation.

This is not always easy to fix yourself, but a professional surveyor should be able to advise on the likely cause and best course of action.

Failed cavity wall insulation can sometimes be topped up, but often requires removal and replacement. If this is the cause of the problem, check the age of the insulation – if it’s still under warranty (usually 25 years) contact the installer or insurer to get it fixed before paying someone else to remove or replace it. 

Find out more about cavity wall insulation costs, and how much you could save on your heating bills.

See the cold

This second thermal image is of a front door, seen from the inside. It shows dark blue (cold) areas under the door, around the edges and around the letterbox. 

It’s likely to feel cold and draughty but can easily be improved. 

Using a thermal camera around the inside of your home on a cold day is a good way to identify where your draught-proofing efforts would be best spent. 

There are plenty of cheap and easy ways to block up draughts around your home with a little DIY know-how. 

Find out how to draughtproof your home to help keep your home cosy this winter and see the results of our draught excluder tests to get started.

Professional or DIY?

If you engage a professional to carry out a thermal imaging survey, they will know what to look for and what the images mean. 

Following the survey, they’ll provide you with a full report detailing any areas of concern. To find a local surveyor, search for heat-loss survey, thermal survey, thermal imaging home inspection or Infra-Red Thermography (IRT). Prices start from around £300+ for a small property to more than £750 for the largest homes.

Here's what you should get for your money:

• High quality images: Professional thermographic surveyors use high-quality cameras costing upwards of £10,000, which have far higher resolution and accuracy than the phone plug-ins. Expert cameras can detect subtle temperature differences as low as 0.02°C, whereas an entry-level camera may only register a 1.5°C difference.
• A thorough survey: Your surveyor should photograph all external surfaces and the inside of all external walls, floors, windows, doors, plus upstairs ceilings, using their expertise to focus on areas where heat may be escaping.
• A detailed report: A room-by-room description, including photos of each room, and an overall summary of all thermal elements (windows, doors, walls, floors and roof).
• Expert analysis: A basic survey report may end there, but many surveyors offer a more in-depth report detailing the property’s construction and architectural heritage, any damp and defects, cold bridging, draughts, ventilation, and existing insulation. They can also recommend improvements to rectify any issues identified.

Although using a thermal camera to produce images may be straightforward, an experienced thermographer knows what to look for, and how to interpret the images.

Whatever your thermal survey uncovers, the real expertise lies in knowing whether you need to spend a few pounds on DIY draughtproofing, or a larger sum to rectify structural, insulation or damp problems. 

Rent or buy a thermal camera

If you have access to a thermal camera, you can do your own survey. The cheapest option is to borrow one. 

Octopus Energy has a camera loan scheme for customers; however, it’s so popular that it’s now closed for this winter.

Some local councils also operate a thermal camera loan scheme. Check with your local library or council website to see if there’s a scheme in your area.

The cheapest camera rental is likely to be through a community-based organisation. The London Library of Things network has thermal cameras available in some locations from £15 a day. You can also check this Library of Things directory to find a location near you.

If you have a local community energy group or one-stop shop, check to see if they offer a camera loan or hire scheme. Some also carry out thermal surveys for a fee.

Tool hire shops rent out thermal cameras, usually by the week, at rates from around £100-£200; however, you may also have to pay a hefty security deposit of £500 or more.

If you’re unable to find a local loan or hire option, you could buy a thermal camera. Affordable versions are available that plug into Android or Apple phones. You can pick one up for less than £200, but these cameras are much lower quality than the ones used by professionals, so your images won’t be as accurate. 

How much can you save?

Draughtproofing is the cheapest and easiest DIY fix and can typically save around £35-£50 a year on energy bills. But it’s not just about savings; draughts make you feel chilly so eliminating them will make your home feel more comfortable at a lower temperature (and you won’t need to pile on the blankets).

Adding insulation to walls, roofs or floors is more expensive – and often a professional job – but can cut heating bills by hundreds of pounds a year. Depending on the size of your home, installing 270mm of loft insulation can save £180 to £340 a year, while installing cavity wall insulation can save up to £370 a year. 

Find out more about the costs and savings of installing loft insulation.