low carbon lichfield
Sept 2010
FACTSHEET
Boilers, Home Heating and Hot Water
Conventional or Combi Boiler?
If your home is heated by a system of water-filled pipes and radiators, then you have a ‘wet’ central heating
system. Typically, ‘wet’ central heating systems consist of either a conventional boiler, a hot water cylinder and a
cold water tank or a combination boiler, (a combi), which gives you instant hot water without the need for a hot
water cylinder.
Condensing or Non-Condensing Boiler?
Condensing boilers are much more efficient boilers. They can be either conventional or ‘combi’ - a good way to tell
whether you have a condensing boiler is to look for a white plastic pipe running from the back of the boiler on an
outdoor wall to a drain. The higher operating efficiency is made possible by the design of the condensing boiler's
larger, or sometimes a second, heat exchanger. The heat exchanger makes sure that as much heat as possible is
transferred from the boiler's burner and that as little as possible is lost in gases through the flue.
If your boiler is fairly new then it may well be in a higher efficiency band. Below are typical savings which can be
achieved by replacing boilers with new A-rated condensing models and installing a full set of controls. An A-rated
condensing boiler will also use a third less fuel than an older boiler to provide the same amount of heat potentially cutting heating bills and CO2 emissions.
Old Boiler Rating
Possible Saving
(£/year)
Possible Saving
(kgCO2/year)
G ( < 70%)
£235
1,260
F (70% - 74%)
£150
800
E (74% - 78%)
£110
575
D (78% - 82%)
£70
375
Setting Controls
Spending just a little time setting the right temperature and ensuring that the system is only on when required will
help you to cut your energy bills substantially. Your room thermostat should be set to the lowest comfortable
temperature - typically between 18°C and 21°C. Try turning your thermostat down a degree or two and seeing if
your home maintains a pleasant temperature.
Thermostatic Radiator Valves (TRV’s) control the output of individual radiators in individual rooms around the
house. They sense the temperature of the air around them and regulate how much water flows into the radiator –
and therefore how much heat it gives out. TRV’s should not be fitted in the room where your room thermostat is
located, as this is likely to interfere with the operation of your heating system, however they can be fitted to all
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other radiators in the home. If your system already has a TRV on the radiator near your room thermostat, turn it
up to the maximum setting.
If you have a programmer or timer, set it so that the heating only comes on when needed. If you are out of the
house during the day then it shouldn't be left switched on all the time and for most people, it won’t be needed at
night while asleep. Most programmers are 24 hours, but for a few more pounds it is possible to buy a 7 day
programmer which allows for more flexible programming.
Modern homes generally warm up quite quickly and can retain a comfortable temperature for a while. Older
homes, particularly those with solid walls, can take a while to warm up. On a cold evening, time how long it takes
for your house to warm up from cold to a comfortable temperature – this is the warm up time. Once the house
has reached the set temperature, turn the heating off completely and time how long it takes for the house to cool
slightly until it’s starting to get a bit less comfortable – this is the cool down time.
You can now set your programmer so that the heating switches on in the evening, just in time to get your home
up to the right temperature for when you return home, and have it switch off again a bit before you go to sleep so
that the house will be starting to cool down by the time you get into bed. Do the same in the morning so that it
switches on a bit before you wake up and switches off just before you leave the house.
The boiler thermostat controls the temperature of the water flowing out of the boiler into your heating system.
If the flow temperature is too high, your heating will not be operating efficiently. This is particularly true of
condensing boilers which operate most efficiently when the temperature of the water returning to the boiler is
below a certain level. If it is set too low, your home will not reach the desired temperature. Typically, a boiler
thermostat is controlled with a dial that has either a range of numbered markings or a maximum and minimum
setting. This will typically let you set temperatures of between 50°C and 80°C.
The boiler thermostat should be set to a higher setting when the weather is cold and turned down to a medium
setting when it is a bit warmer. By adjusting the boiler thermostat as the temperature drops through the winter
and then rises towards the beginning of spring, your boiler should operate more efficiently. If you do not have a
room thermostat, the boiler thermostat is the only way to control the temperature of your home; the setting you
need will have to be tested by trial and error.
'Bleed' radiators from time to time to remove unwanted air from your heating system and keep your radiators
working at their maximum output. The heating system should be switched off when you do this so that more air
isn't drawn into the system.
If you improve the energy efficiency of your home, perhaps by installing loft or cavity wall insulation, your house
will heat up and cool down at a different rate. In order to maximise the savings which you can achieve from the
insulation, try reducing the time your heating system is switched on.
Hot Water
Your water needn't be heated to too high a temperature. Your hot water cylinder thermostat should be set at only
60°C (or 140°F). Any higher is a waste of energy; any lower and there may be risks of Legionella bacteria
forming.
Your hot water should also be set to come on only when needed. It is a common misconception that it is more
efficient to leave your hot water on all the time - this is not the case. It takes a certain amount of energy to heat
the water in your hot water cylinder to the required temperature. If you switch it on just in time to heat up the
water for when you need it, it will use this amount of energy; but if you have it on for any longer, you will need to
keep adding energy to keep it warm. More energy means more money…
For most households the water will be switched on once for the morning and once for the evening. If your home
has low hot water demand and a well insulated cylinder, it may be sufficient to have the hot water come on once
just before you wake up only, with enough warm water being left over to clean the dishes that evening.
Experiment to see which works best.
If your tank has an old, thin insulation jacket, fit a BS Kitemarked insulating jacket, 75mm or 3 inches thick,
around your hot water tank. It can save you around £35 a year - and as it will only cost around £12 to buy, paying
for itself in well under a year. Insulate the hot water pipes that run between your boiler and hot water cylinder - to
save an extra £10 a year. This is best done when you have access to the pipes - for example when pipes are
exposed during renovation work. If you are considering buying a new hot water cylinder it may be an idea to
choose a twin coil cylinder that would allow for a solar water heating system to be added in at a later date.
Further Factsheets are available on using solar energy for hot water and electricity generation.
Reducing our carbon footprint one step at a time
lowcarbonlichfield@hotmail.co.uk
07746 231709
Reducing our carbon footprint one step at a time
lowcarbonlichfield@hotmail.co.uk
07746 231709