Low Energy House - Domestic Heating Controls - Efficient Central Heating
The installation of a sophisticated heating controls package on a domestic central heating system can save up
to 40 per cent on fuel costs. Domestic heating controls may be upgraded at any time but the most cost effective
time is when the boiler is being replaced or when work is being carried out on the heating system
Domestic Heating Control System
A domestic heating control system will ensure that rooms are heated to the temperature specified for the length
of time it is required. It can be turned off at night when heat is not required and off during the
day as the outside temperature rises. The controls need to be flexible enough to carry out the required
tasks but simple enough to understand. Domestic heating control systems are available for hard wired circuits and wireless systems are available for existing houses, where fixing new wiring may be problematic.
A domestic central heating system will normally have the following heating controls:
- Boiler thermostats to control the water temperature in the boiler
- A programmer capable of timing the space heating and the domestic hot water separately
- Room air temperature thermostat
- Hot water storage cylinder thermostat
- Thermostatic radiator valves to give individual control of radiators
- Motorised valves to provide independent control of space heating and hot water
A domestic central heating system may also have:
- A frost and low limit thermostat, to protect the heating system from freezing
- An optimum start controller
Domestic Boiler Thermostats
There are usually two thermostats in a boiler:
- Working Thermostat -
The working thermostat is an integral part of the boiler and allows the water temperature in the
boiler to be pre-set manually. Situated outside the boiler casing, it is usually in the form of a
dial with a range of settings from 1 to 6. It switches the boiler on or off at water temperatures
of between 65ºC - 85ºC. Boilers usually operate more efficiently at higher temperatures.
- High Limit Thermostat -
This is also an integral part of the boiler and is normally pre-set at 90ºC by the
manufacturer. It is a safety feature that closes down the boiler if the working thermostat
malfunctions.
Domestic Programmable Timer
Timers are very important devices for saving energy as they switch the central heating and hot
water systems on and off at pre-determined intervals. Digital programmers are the most flexible as
they can allow for seven day, or longer, functions to be pre-set.
Domestic Room Thermostat
A room thermostat continually monitors the air temperature of the room in which it is located.
It is usually pre-set at about 20ºC and by switching the heating source on and off at appropriate
times maintains that pre-selected temperature. As room thermostats should not be used in conjunction
with thermostatic radiator valves it is usual to locate the room thermostat in a circulation area
like the hallway of a dwelling.
Domestic Frost and Low Limit Thermostat
A frost thermostat is usually installed on the outside of the north wall of the dwelling to
protect the home’s plumbing system from frost. It operates independently of the central heating
programmer and can override it and turn on the heating if the outside temperature falls below
2ºC.
Domestic Hot Water Storage Cylinder Thermostat
To make economic use of the boiler, separate thermostatic controls are necessary for the central
heating water and the domestic hot water. The cylinder thermostat ensures that the water supplied to
the sink, washbasin and bath taps is at a safe temperature. Domestic hot water is usually stored
at 60ºC-65ºC. The thermostat is strapped to the outside of the cylinder where it opens and
closes a motorised valve as necessary to maintain a safe temperature.
Motorised Valves
Motorised valves are electrically operated and are used to facilitate the independent temperature
control of heating and hot water systems.
Domestic Thermostatic Radiator Valves
Thermostatic radiator valves allow the heat output from central heating radiators to be
manually controlled ensuring that the room does not become overheated, thus saving energy. A
thermostatic radiator valve is a combined thermostat and water valve fitted with a dial with a
range of settings that can be operated manually to pre-select an operating temperature. As the
temperature in the radiator rises the water valve closes and reduces the flow of water to the
radiator. Thermostatic radiator valves are ideal for providing background heating in rooms that
are not used regularly.
Domestic Optimum Start Controller
Air temperature varies from day to day throughout the heating season. In view of this, it is not necessary for the boiler to turn on at the same pre- programmed time every day. On warm days the boiler can start up later to attain the pre-set temperature. An optimum start controller is a
computer device that receives information from thermostats inside and outside the dwelling and
calculates the most appropriate time for the central heating to start-up.
The likely payback period for a domestic central heating control system is approximately three years
