Balancing
And Setting Up The Central Heating System
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This is the method I use and is applicable to
the feed and return type of heating system (probably the most common).
General Information
Balancing the system means obtaining similar temperature drops
across all radiators, i.e. they all have a good flow through them.
Ideally each radiator will have a thermostatic valve (adjustable
by a knob) at one end and a flow regulating valve at the other
(usually covered by a cap). Normally there will be one radiator without
a thermostatic valve (usually in the bathroom). The objective is
to get the temperature drop across all radiators to be about 12
degrees Centigrade (20 degrees Fahrenheit). The hotter end of
the radiator is the 'flow' and the cooler the 'return'. If the
pump flow rate is too high the temperature drop across the radiators
will be less than 12C on a properly balanced system. Once a system
has been balanced it should only need redoing if modifications
(including improved insulation) or repairs are carried out. Before
starting it is worth recording the temperatures and the position
of each valve so if it all goes wrong at least you can get back
to where you started. It is quite common to come across systems
that have never been balanced or balanced very badly.
Setting up the system means adjusting all the
various thermostatic valves, thermostats and the pump speed to
give the desired temperature in each room for the least energy
use. Doing this is a way to improve the efficiency of the system and save money and energy whilst helping the environment at the same time.
Measuring Temperature
I have used both a digital thermometer and a non contact infra
red thermometer (which is easier) to do this. See Temperature
Measurement Tips for more information on using these devices.
Process
If you are anything like me this usually turns
into an iterative process, so rather than trying to remember everything
I made up a simple chart for listing all the rooms/radiators with space
to write the position of the flow regulating valve plus the flow
and return temperature and the difference several times. Last time
I did this it took me four goes to get it right. Because not all
flow regulating valves are the same you need to work out how to
record their position, I use 0 for fully closed and then count
upwards in quarter turn increments as I open them. The record sheet
I used can be found in the Checklist
Index .
1. Record initial thermostatic valve and flow regulating valve
positions plus the room thermostat setting, the boiler thermostat
setting and the pump speed (if adjustable).
2. Make sure any zone control valves are open.
3. Open all thermostatic valves fully if fitted.
4. Open all the flow control valves fully.
5. Set any room thermostats to maximum.
6. Bleed all the radiators with the system running to ensure there is no air in them (plus
any other bleed valves in the system - often there are two in the loft).
6. Turn off the hot water heating circuit (if possible), turn off the
boiler, make sure any zone control valves are open and let
the system cool down fully.
8. When the system has cooled down, turn on the boiler.
9. As the system warms up, go round the radiators
and identify the flow and return connections (flow gets hot first).
10. Find which radiators are heating up the quickest.
11. While the system is still warming up turn down the flow control valves of
the hottest radiators so that the cooler ones "catch up". This
gives the start of an approximate balance.
12. Go round with a thermometer and complete a set of
results on the chart. Working out the temperature drop of each
radiator by subtracting the lowest temperature (return end) from the highest temperature (flow end).
13. Go round again closing the flow control valves on the radiators
with the smallest temperature drop. The valve on the radiator with
the highest drop should be left wide open.
14. Repeat 12 and 13 until all the radiators
are fully hot all over and the differentials are as close as you
can get them (it probably won't be a differential of 12C).
15. Adjust the boiler to give a flow temperature of 80C and the
pump speed to give an average differential of 12C across all radiators.
16. If the pump speed is changed it may be necessary to repeat 12 and 13 until all the radiators
are fully hot all over and the differentials are as close as you
can get them to 12C.
17. Where fitted set all thermostatic valves to achieve the desired
temperature in each room.
18. Refit the covers to the flow control valves.
19. Reset the room thermostat to give
desired room temperatures (see confusion between room and radiator thermostats below).
20. Turn down the boiler as low as possible while still achieving
the required temperature in each room. You can always turn it up
if there is not enough heat in cold spells.
21. Measure the temperature of the flow and return pipes near
to the boiler. This gives a useful indication when compared with
the pipe temperatures at each radiator how well insulated the pipes
are. The temperature drop is also affected by the flow
rate, water temperature and ambient temperature. Higher rates
give lower differentials.
Confusion Between Room And Radiator Thermostats
If a room thermostat is in a room with radiators with thermostatic valves you will need to decide which is going to control room temperature (often the room thermostat will also turn off heating to the whole house when it's set temperature is reached). The best compromise if not all radiators have thermostatic valves is to set the thermostatic valves for slightly higher than the desired room temperature and then the room thermostat to the desired room temperature temperature. If all radiators have thermostatic valves it is not worth bothering setting room thermostats.
Thermostatic Valves
There are two main types, the older uni directional type which must be fitted on the 'flow' side of the radiator and need to be the correct way round for proper operation (valves fitted the wrong way round can cause a knocking sound from the system) and the newer bi directional type which can be fitted either way round and are sometimes found on the 'return' side of the radiator.
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