One of the key requirements of any home is to have
an efficient heating system. If there is a gas supply
available to the premises then this will probably the
most efficient running cost.
Lets first talk through some of the key components
of a heating system before we get in to too much detail. |
Boiler
First the heart of the system is the boiler. There are
various types of boilers and some of the main types
are indicated below;
Conventional flue boiler is where the flue is connected
to a chimney and discharged usually at roof level. The
boiler takes its combustion air from the room so it
is important that there is a permanent opening to the
out environment (there are special regulations dictating
the area of the openings).
Room sealed boilers are ventilated by ducting fresh
air direct from outside to the boiler combustion chamber
which is sealed from the room. This sort of boiler is
best suited in a kitchen where there are kitchen extract
fans operating and there is no risk of sucking in fumes
through the flue.
Other types of boiler can be provided in the form of
back boilers an situated in a fireplace in the lounge.
The boiler unit is ventilated using a conventional flue
arrangement. The boiler heats water for the heating
and hot water use. In the front of the boiler a separate
gas fire is provided which heats the room.
One of the latest types of boilers having a high efficiency
is a condensing boiler. With this type of boiler additional
heat is extracted from the warm flue gases which condense
to a vapour. Efficiencies can be up to 20% greater than
with other type of boilers. The down side on these boilers
is that they are more expensive and often there is a
plume of steam discharging at the flue terminal.
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Boilers can be supplied in various combinations and
can be used just to heat water which is then used to
heat the building through radiators and then indirectly
heat hot water for the basins and baths. The alternative
is called a combination boiler which contains package
control systems, pumps and facilities to provide water
for domestic hot water use. This is often easier to
install but can be more expensive to maintain especially
if the boiler is no longer manufactured.
Picture shows a room sealed 29kW output boiler fitting
neatly under a kitchen worktop.
Radiators
Radiators are heat emitters which supply the heat to
the various rooms. Radiator technology has changed over
the years from cast iron heavy radiators to pressed
steel. These incorporate fins to increase the surface
area a give a higher output of heat. Aluminum radiators
have also been popular giving the opportunity to create
special effects in a modern environment.
Radiator heat output is expressed in Btu/hr or kWh
Example of a pressed steel radiator with fins
The radiator selected for the room must been sufficient
capacity to heat the room when it is cold outside at
freezing temperatures. The heat required for each room
will vary depending on its size, thermal properties
and the temperature you require in the room. Buy Radiators
online |
Heat loss calculation
The heat loss calculation indicated below is a simple
example of how the heat requirement is calculated for
a room. Our chart to how hot you should heat each room
in your home will help you calculate the required radiator
size and output [here]
First the air volume must be heated – Measure
the room length height and width in metres and multiply
by 0.33 and then by the number of air changes an hour
you expect that room to have. Generally this will vary
from 1 to 2 depending on its location and use.
The next step is to calculate the heat loss through
the windows. Measure the area of the windows in square
metres and then multiply by the thermal properties of
the window i.e. The ‘U’ value. For a single
glazed window the ‘U’ value will be 5.8
w/m2/degC and 2.9 for double glazed windows. If you
have very special glazing system the ‘U’
value may be different so check with the manufactures.
A quick ready recknoner is provided here to help you
work out the output required from your radiator to heat
your room [guide]
The heat loss through the external walls is calculated
similar to the windows. Measure the area of the external
wall and multiply by the ‘U’ value which
could range from 1.5 for a conventional cavity brick
wall to 0.3 if highly insulated. Again you will need
to check with the manufactures. Heat losses through
the ground floor and roof are also calculated in a similar
way. When all the surfaces which are lose heat have
been calculated add up the total and also include the
air volume. This will give you a value fore the room
expressed in watts/degC. Multiply this by the maximum
temperature you wish to heat the room usually 21 degrees
C. with an outside temperature of –1degreeC. This
represent a temperature rise of 22 deg C. This value
will now be the heat required in Watts to heat the room.
If you want this value in kW the just divide by 1000.
Example calculation for heat loss |
| |
Length |
Width |
Height |
Factor |
Air
Changes |
w/m2/degC |
| Glass |
3.3 |
3 |
2.3 |
0.33 |
2 |
15.03 |
| External
Wall |
3 |
|
2 |
2.9 |
|
17.4 |
| Floor |
6 |
|
2.3 |
1.5 |
|
20.7 |
| Total |
|
|
|
|
|
63.03 |
Room temperature required 21 degree C when -1 outside
= 1386.62w |
Domestic hot water
The domestic hot water system is also provided in conjunction
with the central heating system. Heat is supplied from
the gas boiler and there are two main ways in which
this can be achieved.
- By using a combination boiler or
- The more common way by providing an indirect hot
water heating cylinder. Majority of systems use this
method and it prove reliable and flexible it also
has the added advantage that the cylinder can be positioned
in the linen cupboard and the heat emitted by the
cylinder help air the clothes.
|
Control Systems
Controls systems for central heating and hot water systems
can be very sophisticated and you could write a book
covering all the variations.
It is other best to consult the boiler manufacturers
installation instructions as they other put forward
some proven control solutions.
Generally there are two main types of configuration
of a heating and hot water system.
- Pumping water from the boiler to the radiator heating
system with a gravity circulation for the domestic
hot water or,
- A fully pumped heating and hot water system.
There are advantages and disadvantages to each arrangement
but possibly the pumped system may have the edge because
pipe sizes are reduced to the hot water cylinder. A
diverter control valve is used with this arrangement
and this gives the option of running the heating or
hot water systems together or separately.
Typical diagram of pumped heating and gravity hot
water primary flow and return
circulation |
Click on the image to see the full sized diagram
Typical diagram of pumped heating and pumped hot water
primary flow and return circulation. |
Click on the image to see the full sized diagram |
Pipe sizing
Pipes have to be sized to ensure that they allow sufficient
water to flow through the pipes to heat the radiators
and domestic hot water cylinder.
Below is outlined a very simple approach to pipe sizing
for a domestic heating system. The chart indicates approximately
how much heat a pumped copper pipe will convey. As you
plan your system each radiator will be feed with a flow
and return pipe this all connect back in parallel and
as each radiator is added to the circuit you need to
total the heat required to determine the size of the
pipe.
| Size of copper pipe |
Heat conveyed based on 20degc temperature drop. |
| 15mm |
6000 watts |
| 22mm |
14000 watts |
| 28mm |
28000 watts |
|
Installing the heating system
Legally there are parts of the installation you cannot
undertake and these must be carried out by a CORGI registered
Contractor. You can do some of the work yourself such
as positioning radiators and install the heating pipes
(not gas pipes). If you are competent in stalling electrical
systems you may be able to complete the controls systems.
However at the end you must have a CORGI contractor to
connect the gas supply and generally check the installation
for safe working and commissioning of the system. |
Installing the radiators
Start with installing the radiators the normal position
is under the windows unless you have full height curtains
then you may wish to position the radiators on an adjacent
wall. The radiators need to be about 100 –150mm
from the finished floor to allow cleaning underneath and
space for valves. On the flow connection install a wheel
valve (for general isolation) and on the return a lock
shield valve (for regulating the water at commissioning). |
Pipe work
Plan your pipes to run on the surface or under the floorboards.
Remember to make sure that all pipes vent to the radiators
otherwise air locks will be created and the system will
not work. If you do run pipes under the floor mark the
area they are installed in so nails do not damage them.
The fittings can be compression joints or capillary
joints. These are soldered using a blow-torch. Remember
if you do use a blow-torch protect flammable materials
and check that the solder has properly run around the
joint otherwise you will have a leak.
Allow room for the pipes to expand and contract. Also
don’t make a too permanent feature of concealing
the pipes because one day you may have to maintain them.
Route the pipes back to the boiler and also ensure
that the system has a cold feed and an open vent pipe
connecting to the feed and expansion tank which is usually
positioned in the roof space. |
Installation of the boiler
The boiler must be installed and commissioned strictly
in accordance with the manufacturers instructions. |
Commissioning the system
When you have completed all the installation make sure
that all the air vents on the radiators are closed.
Start filling the system with water and vent through
each radiator. Check for leaks. Before turning the boiler
on run the heating pump to ensure that as much air in
the system is dislodged and then re-vent. Never vent
the system while the pump is running. Then turn on the
boiler and as the water warms up balance the water flow
to each radiator using the lock shield valves.
- Check all the controls and safety systems to ensure
the system is working correctly.
- Allow the system to run for a few days then check
for any leaks and ensure the system is fully vented
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Future Maintenance
The boiler will need regular maintenance from an approved
Maintenance Contractor usually about every 12 months.
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