What is a setback
thermostat?
Thermostats control heating and
cooling appliances in houses. A
setback thermostat gives the user the
option of changing the temperature
setting automatically during the
nights and during the work day
when the occupants have left the
house. A setback thermostat can
help reduce overall household
energy consumption.
A conventional thermostat simply
regulates house heating at one
temperature. For instance, in the
winter, if you set the thermostat to
20°C (68°F), it will activate the
heating system when the house
temperature drops below 20°C and
will shut the system off when the
house air warms up past 20°C.
A setback thermostat contains an
electronic clock. It can automatically
turn down the temperature setting
at night, when you are asleep, or
midday, when you are at work. It
can also return the temperature to a
more comfortable level before you
wake up or arrive home from work.
That way you can have the energy
savings of a lowered thermostat
setting without the discomfort of
having to wait for the house to heat
up again.
The setback thermostat can also be
used as a set-forward thermostat for
an air conditioning system. It can
allow the house to heat up when it
is unoccupied and return it to
comfortable temperatures before
you return from daytime activities.
Although this About Your House deals
with setback thermostats and forced-air
heating systems generally, you can
apply some of the advice to electric
baseboards or to summer usage.
You can use a standard thermostat to
set your house temperatures lower
during times when the house is
unoccupied. This will lead to similar
energy savings as with a setback
thermostat but not the convenience.
What is a normal house
temperature?
CMHC has randomly surveyed
Canadian houses. Thermostat settings
in winter tend to be quite closely
grouped around 20–21°C (68–70°F).
Summer temperatures range much
more widely, depending upon whether
the house has air conditioning.
To what temperature should I
set back the thermostat?
The more you reduce the
thermostat setting, the greater the
possibility for savings. Generally, a
drop of two degrees will lead to
some savings and little risk. Some
householders reduce temperatures
four to six degrees. However,
temperature differences this large
create potential comfort and
moisture problems that are
discussed below.
about your house
Setback Thermostats
CE 32
2 Canada Mortgage and Housing Corporation
About Your House
Setback Thermostats
Does setting back the
temperature save energy?
Yes. Research from the Canadian
Centre for Housing Technology,
reported on CMHC’s website at
http://www03.cmhc-schl.gc.ca/
b2c/catalog/Z_downloadpdf.do?z_
pdf=63816.pdf shows that winter
setbacks for the houses tested would
result in heating costs savings of five
to fifteen per cent. The highest savings
came with a setback of six degrees.
Savings for summer were about the
same, although simply raising the
thermostat set point in summer
from 22°C (71°F) to 24°C (75°F)
led to more significant savings than
the set-forward strategy and offers
better indoor humidity control.
Note that these savings are for two
airtight, well-insulated, unoccupied
houses. The savings in your home
may vary, but are likely to be in the
same range.
What can go wrong?
There are several potential problems.
The first one is comfort. A cool
house can be uncomfortable in the
winter. If you wake up at night
before the time the thermostat resets
to 20 or 22°C, the rooms will be
cooler. The same applies if you have
a setback daily when you leave for
work, but you return home earlier.
A setback schedule works best for
people with predictable work and
sleep periods. If your schedule is
completely irregular, you might as
well simply turn down a
conventional thermostat when you
sleep or leave the house, rather than
trying to anticipate it with a setback
thermostat.
A second problem is the possibility
of high humidity in the winter.
Cool air can hold less moisture than
warm air, so the relative humidity
(RH) rises as the air cools. For
instance, house air at a reasonable
35 per cent RH at 22°C will see an
increase to 50 per cent RH when
the same air is allowed to cool to
16°C (61°F). This can lead to
condensation on windows and walls
(for instance, in closets or behind
furniture).
Basically, you are creating a more
humid environment, all things
considered, when you allow the
house temperature to drop
significantly. This may not be a
problem in a dry house or one
where you can modify the humidity,
for instance by turning off a
humidifier. The house humidity
should be monitored, especially in
winter. For more information on
how to measure humidity in houses,
go to Measuring Humidity in Your
Home at http://www.cmhc-schl.gc.
ca/en/co/maho/yohoyohe/momo/
momo_002.cfm
Window condensation will be the
first place that you notice excessive
house humidity. Blinds and curtains
usually increase the occurrence of
condensation. If condensation is
taking place, make sure that you
wipe it up diligently or raise the
temperature setback (eg. from 16°C
to 17°C) until you have lowered
house humidity levels and
condensation is no longer a
problem.
A third potential problem is a
sustained lack of air circulation
as the house cools down.
If you set back your thermostat in
the evening from 20°C to 16°C, the
house may not cool to 16°C until
5 a.m. During that time, there will
be no furnace circulation fan
operation, unless you set the fan
to run it continuously. For houses
where bedroom doors are kept closed,
this could lead to stuffiness in those
rooms and a lack of fresh air.
There are ventilation devices and
furnace fan cycling controls that
can compensate for this, if you
find bedrooms and other rooms
underventilated during setback
periods. Setting back to a higher
temperature, such as 18°C (64°F),
will reduce the period of furnace
inactivity (and your consequent
savings). Setting the furnace fan to
run continuously will help but this
will increase electricity consumption.
Canada Mortgage and Housing Corporation 3
About Your House
Setback Thermostats
The final potential problem with
setback thermostats is the time
required to regain temperature, or
to heat the house up once more.
An oversized furnace will return the
house to the higher temperature
quickly, but a properly sized furnace
can take a long time—as much as
one hour— to bring the house back
to a comfortable temperature. You
have to experiment with this as it
will depend on the type and relative
size of your heating equipment and
your home’s energy efficiency and
other factors.
If it takes an unacceptably long time
for your house to heat up again,
consider a smaller setback or start
the high temperature setting earlier
so that it is comfortable for you
when you get out of bed or return
from work.
Related to this problem is the length
of time required for the room
enclosure and furnishings to heat
up. If your bathroom has cooled to
16°C overnight and the furnace has
kicked in at 6 a.m. to bring up the
heat, your bathroom walls will still
be cool when you start a shower at
7 a.m. Testing in the research house
at the Canadian Centre for Housing
Technology house showed that it
takes up to several hours for wall
temperatures to return to their
highest temperature. Cool wall surface
temperatures can lead to comfort
and condensation problems.
What houses have the
greatest risk for problems?
Many houses will not see significant
problems with the use of setback
thermostats, but there will be some
houses more at risk.
If you have a house with moisture
problems in winter (mold,
condensation on windows, and so
on), get those problems fixed before
you consider installing a setback
thermostat or set back your
conventional thermostat.
If you have a forced-air furnace and
closed bedroom doors, you will need
to ensure adequate ventilation of
bedrooms at night, one way or
another. If you already keep your
house at an unusually low temperature
(such as 18°C), then a temperature
setback is more apt to get you into
the high humidity danger zone. If
you are the sort of person who has
difficulty operating a VCR or DVD
player, you will find many electronic
thermostats confusing, especially
when compared to the simplicity
of an older dial thermostat.