Thermal imaging guidelines and interpretation
A number of local Community Action Groups (CAGs), along with several councils, including OCC,
now own thermal imaging cameras which they are willing to lend out to groups who want to offer
advice to local residents on improving the energy efficiency of their homes. These cameras record
infrared emissions, turning whatever they see into a palette of colours depending on the heat emitted
by the surfaces. Although absolute heat loss is hard to calculate and depends on the different thermal
properties of the structural elements of the building, thermal images can highlight significant areas of
loss. Carried out in conjunction with a more detailed discussion about the building and the ways it is
used, thermal imaging can help inhabitants to plan effective eco-renovation projects, or to adopt
simpler measures which may increase their thermal comfort, lower energy bills and decrease carbon
footprints.
Conducting a thermal imaging survey
External surveys
Imaging the outside of a house will highlight both heat absorbed from the sun or from external lights,
as well as any heat lost through poor insulation or from areas of the fabric of the house which could
benefit from draught proofing. Because the effects of solar load cannot be easily differentiated from
heat loss from within the building, external images must be recorded at least 3 hours after sunset, and
surveys cannot be carried out during or for several hours after rain or in high winds. Surveyors should
also document the weather conditions and note which images are taken from which direction.
Differences due to north and south facing falls after sunny days will be very apparent.
Front and rear of a property- north (left) and south (right) facing imaged after a sunny day
When recording and interpreting images, be alert to the temperature scale shown on the right of each
image: the information is relative to what else is in the frame and the scale used, i.e. ‘cold’ could be
8oC in one frame and 2oC in another. In addition to the temperature scale, the camera also allows the
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user to select one or more spots for an absolute temperature reading- these are indicated by a crosshair
mark, the temperature of which is shown on the image as the ‘spot’ figure on the top left of the image.
This feature can be switched off to keep the images less cluttered.
In order to show heat loss from within the building, the images depend on the presence of a thermal
gradient. Home owners should be contacted in advance and asked to set their heating system to
operate at its full winter setting for at least 4 hours before the agreed session time to achieve a
minimum internal temperature of 18oC throughout the house (a separate file of guidelines for property
owners is available which can be emailed once an appointment has been set up). Under these
conditions, external images will show up areas of heat loss on a palette ranging from blue through
green, yellow, orange and red to white (as indicated by the scale on the right of the image below).
Typical thermal image of a brick house without insulation: the red patch under the left hand window
is a radiator, the wall is south facing and the yellow/green patches are likely a combination of heat
loss due to lack of insulation, and residual heat from the sun. The windows are all double glazed, but
the one on the top right is much newer, while the one on the top left has been refurbished.
In addition to residual heating from the sun, there are other features which are not directly connected
with heat loss through insufficient insulation and to which users should also be alert. Heat (from
within the house or from the sun) can be trapped under the eaves of the roof, showing up as a
characteristic red line:
Different building materials also display different thermal properties which cannot be compensated
for in a simple image, and may cause, for example, lintels and frames of windows to be highlighted.
Some of these kinds of thermal bridges are inherent and cannot be remedied.
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For these reasons care must be taken in interpreting the images, and it can be helpful to try to image a
number of neighbouring properties during a single session and without changing the camera settings.
Together with knowledge of the differences between the properties, this allows for more informative
analysis of the images.
Internal surveys
Alternatively, or additionally, the camera can also be used to pick out cold spots inside properties,
typically areas of leakage or thermal bridging which may coincide with visual evidence of
condensation. Internal images are ‘reversed’, i.e. areas of heat loss show up as dark blue (colder)
rather than red (hotter). Internal surveys are easier to carry out, since they do not depend on clear/dry
weather, and the camera (and operators) is more comfortable! However the images can be more
difficult to interpret, as air currents within the room and other building features can throw up
anomalous patterns in the images.
Camera set up
The camera offers a number of palettes- the rainbow or iron palettes are most generally used for home
inspections. There will probably be a twist lens focus, as in ordinary cameras, which needs to be
adjusted to get a sharp image. Finally thermal tuning the camera involves adjusting the span or
temperature range that the camera sees while in manual viewing mode. Thermal imaging cameras will
have an automatic viewing mode and manual viewing mode. When the camera is in automatic mode,
the camera will automatically adjust the temperature scale to what is being viewed which causes the
display to change colours frequently when the camera is moved. Manual mode allows the user to
adjust the span to a desired range and the camera will always display this temperature range. Using
the manual mode is the best method to bring out temperature differences of the object being viewed.
Setting the camera to manual mode
 At the beginning of the survey, toggle the ‘ok’ button to check the camera is on automatic mode
 Move the camera so that the viewfinder shows a sensible template range (as a guide, the
temperature range being shown should be between -5°C to 10°C)
 Fix this temperature range by pressing the ‘ok button to set the camera to manual mode.
 If necessary, use the up and down arrow buttons to shift the fixed temperature range so that the
colours shown in the image looks appropriate (for example you may want to push the range down
a little bit to make the hottest areas of the image stand out more).
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Because thermal energy can be reflected from shiny surfaces, thermal imaging cameras cannot see
through glass. If you stand in front of a window while looking at a thermal imaging camera, you will
see yourself in the window because of the thermal energy reflecting off the glass. This makes absolute
interpretation of energy lost through windows more difficult, but you will be able to pick out leaks
from around window seals, relative differences between windows in the same property (single, double
or triple glazing, use of thickly lined curtains etc).
After taking images of a number of nearby properties, including detailed photos of some of the
features discussed below, the camera team could then try to engage residents in conversations about
different features and behaviours in their homes (for example use of thick curtains, radiator foil, any
differences in insulation etc.) If the homeowners have filled out the information form about their
properties in advance, this will allow the camera team to be better prepared with information which
may be relevant to the properties being surveyed.
Within a typical North Oxford property there are a number of building features which are highlighted
by thermal imaging, and for which renovation measures are possible.
Solid walls
One of the most dramatic examples seen in last year’s surveys was of the impact of the solid walls
typical of homes in this area. One home had lined their walls inside with insulating material on
battens to create a warm inner surface; while others complained of rooms which had lengthy runs of
cold external wall punctuated by windows. This is possibly the most difficult problem to tackle:
external insulation is best (and most expensive), dry lining a good alternative if space and budget
allows; and cheap and cheerful is lining with Sempatap. If you are considering building an extension,
or renovating an existing part of the property, these options are worth investigating. However care
should be taken to allow sufficient ventilation and to avoid the creation of cold patches at joins in the
insulation, and the possibility of moisture condensation between the insulation and the wall.
An un-insulated stone house (17th Century) on the right, with a new Celotex insulated extension on the
left: the line is clearly visible in the centre of the picture
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If solid walls cannot be insulated for financial or planning reasons, it is worth looking at other
measures to reduce heat loss, e.g. the fitting of radiator foil behind radiators located on outside walls.
Before (left) and after (right) installation of radiator foil. Note also that in the right-hand image,
although the foil has cut down on heat loss, there are still patches where the radiators are fixed to the
wall and conducting heat away from the room. In addition in the right-hand image the curtains have
been left open on three windows to show how much heat loss can be caused.
There is a range of products for reducing the heat loss through the wall behind a radiator. The
simplest and cheapest is a sheet of aluminium cooking foil attached to the wall with adhesive tape.
Next in cost is attaching the foil to sheets of cardboard that fit behind the radiator. Special radiator
foil can be used (about £7 a roll) attached with wallpaper paste or there are versions which are
suspended behind the radiator (good if you have stone walls) Finally the most expensive option is to
buy light-weight contoured ‘silver’ panels at a cost of £5 - £10 a radiator. A shelf above the radiator
helps to spread heat into the room.
Cavity Walls
Where the property is over a period for which cavity wall insulation is an option, this remains a very
good investment. Although there are less grants available, it may still be possible to get help from
your energy supplier (http://www.which.co.uk/energy/creating-an-energy-savinghome/guides/energy-grants/energy-grants-from-energy-suppliers/)
Neighbouring properties with (right) and without (left) cavity wall insulation
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Windows
External images of windows do not show absolute loss relative to the walls due to the different
thermal and reflective properties of glass; however comparison between windows can be
instructive:
Modern double glazing (upper windows and front door)
performs better than older double glazing (bottom right)
Images recorded from inside on cold evenings always show up even the best double glazed windows
as blue – or at least with blue tinges where the draft leaks in and cools the frame. The standard to
match now is moving not to double glazing, but to triple glazing. However this is still expensive, as is
replacing any window, especially if it’s an intricate sash design. What the camera revealed was how
much can be done with window coverings. The best example seen was a house where the windows
were covered both with blinds and then curtains on top: very little heat escaped leaving the rooms nice
and cosy. In addition, investing in curtains with thick thermal linings can cut heat loss through
windows. Make sure they don’t hang over a radiator preventing the heat from getting into the room,
and remember to draw them at dusk.
An image from inside the house which shows how cold windows
are, and the importance of keeping curtains closed.
Secondary glazing is helpful and comes in many different forms, the cheapest being shrink wrap (like
cling film) held in place with tape and smoothed by being gently warmed with a hair dryer. Some
handymen can make secondary glazing on a wooden frame with shrink wrap (I have an Eynsham
supplier for this). Magnetic panels are also relatively cheap and easy to fix to most windows.
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Chimneys
The joys of having open fires are always balanced by the impact of open chimneys. Open fires,
wonderful as they are, are very expensive both of fuel when they are alight but of heat when they are
not. Images outside houses with open chimneys show a whit gash of heat in an otherwise cold wall:
chimney balloons and chimney sheep are a simple way to block the flue temporarily.
Doors
Front doors, even when closed, show how leaky they can be. A 1 mm gap all the way round a door
adds up to the same area as an A4 piece of paper – like a massive ever open letter-box – so it is well
worth paying attention to draught proofing. For sides and top, self-adhesive foam or rubber strips are
effective. For the larger gaps, especially for outside doors, more robust rubber, plastic or part metal
strips which need to be tacked into position are best. The bottom of the door can have a self-adhesive
or tacked on plastic strip incorporating a brush. If you are keen to do the job as economically as
possible, a strip of heavy felted material stapled into position works well. Letter box covers (or a bit
of fabric hanging in front of the box) on the inside are helpful.
Image of the inside of a front door showing the cold spots between the door and the frame.
The most effective solution is to have an outer door to create an airlock effect and this makes a
dramatic difference. If that cannot be achieved, then the old fashioned method of deploying a curtain
across the aperture works well. This can be complemented by a “portiere” which lifts the curtain a
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little as the door opens allowing it to fall all the way to the floor. And if a curtain is a little clumsy all
year, remove it for the summer.
Suspended floors
Another lesson learned was the impact of floors, especially where the floor is suspended. One
homeowner has decided to properly insulate their basement ceiling as work is about to be done;
another is covering their leaky timber floor with a cork layer. Both will increase the comfort and
reduce the heat losses.
Around floors, also pay attention to skirting boards, pipes and cables: the gaps need filling. The
cheapest method is to make papier mache with torn paper (newspaper is fine) and diluted PVA glue
and press it into gaps. Alternatively use a commercial filler or an expanding foam. The foams are
quite tricky to use but are ideal for large gaps.
Internal image: blue areas are cold air of draughts at edges of and between floor boards.
Loft insulation
The easiest escape route for heat (about 25-30%) is through the roof if it is un-insulated. Current
recommendation is for 30 cms thick insulation. This can be a DIY job (using a good mask), but as it
can be rather unpleasant, you might want to think about paying someone to do it for you.
Photo and internal themal image showing how easy it is to spot missing attic insulation.
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Photo and thermal image of loft hatch taken from inside the attic: the red areas show that the
gap is leaking hot air into the cold the roof space...
Image of a stairwell of a house built in 2002. Investigation showed that the builders had
failed to insulate the space between the ground floor and 1st floor under the integral garagethis resulted in un-vented air entering the cavity wall (stair wall) and floor space of two
bedrooms. The blue areas at the edge of the stairs and along the bottom of the stair wall
show that cold air is leaking into the house here due to the lack of insulation.
Hot water tanks
If your hot water is stored in a tank rather than supplied from a combi-boiler, remember to give your
hot water tank a cosy jacket, which should be at least 75mm thick. This could take less than a year to
pay for itself. If they are accessible, it’s also easy to lag your hot water pipes. Just check the
dimensions before buying the lagging.
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Other areas of energy wastage- lighting and appliances
Another use of the camera lies in finding hotspots indoors, rather than the expected cold spots. Bright
white pinpricks of heat are observed from small halogen lights (the bulbs often burning at 80 degrees)
where an LED would produce virtually no heat.
Most of these bulbs are simply replaceable but make sure you install the correct voltage. The
traditional tungsten filament bulbs give out most of their energy as heat. Modern compact florescent
(CFLs) are much more efficient. They are now reasonably quick to warm up, can be obtained in a
large variety of fittings. The most efficient bulbs available are LEDs. At the moment they are more
expensive but they light up instantly. They are particularly good as replacements for halogen bulbs
(such as the ones often recessed into ceilings) because, for example, 4W replaces 50W which gives
you a huge saving. CFL and LED bulbs are straightforward replacements except where dimmer
switches are used.
Electrical equipment is another source of surprisingly large levels of heating, for example from printer
transformers, phone plugs and other electrical equipment which we tend to leave on all the time.
Some of these devices are producing heat even when the device is switched off.
Small wireless switches can easily be purchased which turn off sets of equipment when you leave the
room without having to disconnect the plugs each time.
Notes
1 Sempatap comes on a roll and is DIY doable: see http://www.mgcltd.co.uk/sempatap-thermal
2 Triple glazing: examples at http://www.rawington.com
3 Chimney sheep and chimney balloons at www.chimneysheep.co.uk and www.chimneyballoon.co.uk
4 Portiere rods from http://www.tracksandpoles.com/rod_portiere.shtml.
5 Wireless switches from http://www.domialifestyle.com/Index.asp and look for Bye Bye standby.
6 LED lights from any good website including www.efficientlight.co.uk
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A few questions to help spot energy waste

Have you a modern boiler with its timer set suitably?

Do you have a room thermostat?

Do you also have radiator thermostatic valves and match their settings to suit the use you make of
each room?

Is your hot water tank (if you have one) well insulated?

Are all your light bulbs efficient?

Do you have double glazing?

Do you use curtains in the best possible way?

Do you keep internal doors shut? (This reduces draughts within the house and helps keep the
warmth where you need it).
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