is clear that some heat pump installations have
fallen short of the energy efficiency that they
could achieve. They are a little less forgiving
then convention systems, and usually require a
bit of care to set up correctly.
Heat pumps are different to the conventional
central heating systems that we are used to.
The energy efficiency is affected greatly by
the working temperatures that they are operating
at. The variation in energy efficiency can be
dramatic, and can be caused by a number of issues.
We are used to heat-on-demand heating, but
heat pumps tend to be slow-response. To get
the lowest running costs, you will need to plan
ahead and ensure that you allow plenty of time
for the house to warm up slowly.
Note: - due to the large number of different
heat pump types, with many possible configurations,
it is impossible to give suggestions that would
suit everyone. The integral central electronic
controller (fitted to most models) has a host
of parameters that could be adapted to suit
a particular installation in a specific house.
Unfortunately, these are not always set to their
optimum for energy efficiency, and usually require
a product-specific trained expert to advise
The notes below could be helpful, but there
is a risk that they may confuse or worry. My
apologies if they do. Always seek expert advice.
Keeping the heated water temperature
This cannot be emphasized
It seems counter intuitive to think that a
heating system is more efficient if it’s
heating at a low temperature level. However
this is the case with heat pumps. A heat pump
is happiest if the radiators or under-floor
heating are taking the heat away as 'quickly'
and efficiently as possible. This is why radiators
should be as big as possible. This reduces the
temperature of the circulating water, and increases
the COP(energy efficiency).
Heat pumps usually have an integrated digital
controller that has a multitude of functions.
However, some have a simple knob or digital
control. Whatever control you have, it should
be set so as to achieve the lowest circulating
water temperature that you can get away with.
i.e. the minimum temperature that gives adequate
room heating. (any room or radiator thermostats
are another matter).
Try a lower water temperature, and see if the
rooms are still warm enough. Adjust frequently
if you have the inclination. This will give
you the lowest running costs. If you are using
a time control, you can achieve lower temperatures
by increasing the time that the system is 'enabled'.
i.e. reduce the 'off' periods.
For every two degrees reduction, you may save
around 5 % in running costs, for the same heat
output. This shows how important the settings
This is the automatic adjustment of the heated
water temperature dependant on outside conditions.
The system automatically adapts to outside conditions,
and potentially saves a significant amount of
energy. Interestingly, this control alone, if
set correctly, can maintain a reasonably constant
room temperature with no actual room thermostat.
Most heat pumps have a weather compensation
function, and it is generally set-up by the
installation engineer. It usually has a ‘virtual’
room temperature setting that the control is
aiming to achieve( e.g. 20°C), and also
a ‘heating curve'. Other weather-compensation
controls have various heated water temperature
settings that depend on outside temperatures.
Whilst the initial setting is usually estimated
by the installing engineer, the final setting
is best made by the occupier using the method
of trial and error.
If you are uncertain about the setting, you
may need to sit down with your user instructions,
and a cup of tea. (Many user/installer manuals
are available on-line.)
The setting for weather-compensation can be
adjusted down(reduced) until the heating is
just inadequate, then turned back up a little.
This has to be done in various weather conditions,
and could potentially save you a significant
amount of energy.
If your house need to operate with a high setting,
then you may need to investigate why: - is your
under floor or radiator system circulating water
Are there unwanted restrictions in your system?
The anomaly or weather-compensation
and air source heat pumps.
On frosty nights, your weather-compensation
control will automatically increase the heated
water temperature in an attempt to match heat
demand. If your system is air source, then it
will by nature be less energy-efficient during
this frosty night. If the following day is warm,
the water temperature setting will automatically
reduce. In essence, the control is encouraging
the system to run more during the frosty night,
and less in the day.
If your house has a reasonable amount of internal
brick or stone, it is said to have a high 'thermal
mass'. Such buildings will retain heat during
the frosty night, and could actually take advantage
of the day's heat by storing some of it. Ideally,
the air source heat pump would be encouraged
to operate for some of the day at high efficiency,
and with limited running at night.
Sadly, it seems that no controllers are advanced
enough to deal with this intelligently yet.
Suggestion: Use the set-back
facility in the controller to partly discourage
night time running. This might help. i.e. reduce
the required room temperature by 1.5 to 2 degrees
Warning - Make sure this action does not increase
the use of any electric back-up heater (see
below). i.e. if you reduce the hours the heat
pump runs per night, then it might call on the
electric back-up at some other time in the day,
so its always important to keep an eye on this.
Back-up/ auxiliary/ supplementary heaters
Many systems have an internal electric auxiliary
heater; this is designed to only operate occasionally
when the outside temperature is particularly
cold. High running costs could be due this heater
operating too often. There are many reasons
why this may happen, and it is more likely to
be a problem if the heat pump is undersized.
However, MCS accredited heat pumps should not
All controllers have ‘system information’.
This should include a record of the total hours
that the heat pump compressor and the auxiliary
heater have clocked-up. This is worth keeping
an eye on. Note down the hours and the date
Some heat pumps allow you to switch off the
electric heater. However, care should be taken
to ensure that any legionella protection for
the hot water cylinder is still satisfied.
Most heat pumps allow you to limit or minimise
the amount that an electric heater is used,
but its rarely simple to configure.
Remember, it is the cold spells like early 2010
when this heater is likely to be over used.
I repeat – by limiting compressor use
(too many degrees of night setback), there is
the possibility of increasing the electric back-up
use. Compressor running is always preferable
to the electric back-up heater.
Top Tip - If you are wasting
energy and money by your internal boost heater
coming on when it should not, it would be worth
fitting a 'house
energy monitor' to your heat pump's
supply (not to the whole house). These often
have an alarm function, so they could alert
you when the boost heater is coming on due to
a sudden increase in the input power. You could
then investigate the settings if you want to
(note, these devices often indicate inaccurately
high compressor power. However, they will inform
you when the expensive boost heaters come on)
Room temperature control
Whilst weather compensation alone could maintain
reasonable room temperatures, it is normal to
have room thermostats, or sometimes, radiator
TRV’s. (thermostatic valves)
If TRV’s are fitted to your radiators,
your heat pump will not like it if too many
of these start to turn off.
Tip:- turn up
TRV’s in main and central rooms, and control
the room temperature in these rooms by adjusting
down the heating curve or setting on the heat
Use TRV’s to limit the temperatures in
the extremity rooms/bedrooms only etc.
Time clocks are not ideally suited to heat
pumps. This is because the house can cool off
too far on a cold night, and struggle to get
back up. By using a reduced (rather than off)
night setting, you will find that the heat pump
will rarely run at all on milder nights, but
it will stop the house cooling too much at night
in mid winter. Programmers with different day/night
temperaures are better than on/off timers.
If you do however run with a timer, try running
for longer and start the heating earlier. This
can allow you to drop the heated water temperature.
Unlike boilers system, heat pumps are happiest
with a much earlier start.
If you run continuously, consider using 1 or
2 degrees night-setback. This may save you a
little, and may or may not be worth the trouble
If your heat pump switches on and off many
times per hour, then investigate why. Heat pumps
ideally would operate for periods of 15mins.
or much more.
If your hot water cylinder is enabled to keep
warm all the time, you may be wasting energy.
A lagged cylinder will store hot water for a
considerable time, and it is not ideal if your
system is frequently topping up the cylinder.especially
if there is a distance between your heat pump
and cylinder. Ideally you would have timed 'off'
periods. During these periods, the water in
the bottom of the cylinder will become cool,
and at the start of the 'on' period, the
heat pump will easily heat the
water from cold before it strives for higher
temperatures. The average efficiency is better
if you can manage to program the right off periods
in. The risk here is that you could run out
of water at the end of an 'off' period, so you
may need to experiment by trial and error.
Keep the temperature of the water passing through
your heat pump low
Don’t restrict the water flow through
the heat pump.
Try more continuous-heating with a low water
Try 1.5 or 2° setback overnight, especially
with air source.
Minimise the use of auxiliary electric heaters.
Record the run hours for both compressor and
electric heater. Keep a close eye during very
Fit an energy
monitor to the heat pump