|Bleeding Radiators||Central Heating Set Up||Pipe Insulation|
|Radiator Efficiency||Radiator Faults||Thermostatic Radiator Valves|
|Boiler Types||Central Heating Control||Temperature Measurement|
Balancing the central heating 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 (also known as a lock shield valve) at the other (usually covered by a cap). Often 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. Zone control valves are fitted to some systems to enable some areas of the house to be turned off or kept at a different temperature e.g. turn off the heating to the bedrooms during the day. It is important these valves are fully open when balancing the system.
Setting up and balancing the system means adjusting all the various thermostatic valves, thermostats (including the boiler thermostat) and the pump speed to give the desired temperature in each room for the least energy use. Doing this is a way to maximise the efficiency of the system plus save money and energy whilst helping the environment at the same time.
Before embarking on what can be a time consuming process it is worth finding out whether the system needs balancing. With the system at normal working temperature and all thermostatically controlled valves on the radiators fully open (remembering to record their original positions) measure the temperature difference across each radiator. If this difference is significantly different from 12 degrees Centigrade (20 degrees Fahrenheit) for any radiator then adjustment is required. If all radiators have a similar drop that is not 12 degrees Centigrade (20 degrees Fahrenheit) it may only be necessary to adjust the pump speed and/or boiler temperature - see step 17 below onwards. If any radiators are significantly cooler at the top compared to the bottom then try bleeding the radiator before measuring the temperature drop. It is a waste of time trying to do this on a hot summers day as the system will probably not need to work at all and some strange results will occur. If any radiators are not working at all and they used to work try bleeding the radiator. Don't forget that towel rails in bathrooms heated by the system need to be dealt with just like radiators. If these tips don't solve the problem the radiator faults page will help with suggestions.
One point worth remembering is that having a properly balanced system does not mean all the radiators have to be the same temperature. How hot a radiator is once the thermostatic valves is operating will depend on the size of the room, how well insulated the room is, how often external doors are opened and shut, how high the thermostatic valve is set and how big the radiator is. It is also worth noting that radiators are likely to be slightly hotter at the top than the bottom but this will vary from system to system, room to room, the design of the radiator and the airflow around it. As long as the difference is no worse than the drop across the radiator this is not an indication of a problem.
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 and where insulation is needed. The temperature drop is also affected by the flow rate, water temperature and ambient temperature. Higher rates give lower differentials. If you do decide to do any insulation at this stage then re do this check and the checks in the paragraph above to get the new temperatures, it will provide a good guide as to how much improvement has been made before starting to make any other changes.
There is not much point insulating pipes running within heated areas unless the room is small and the heat from the pipes only mean the room is too hot - in this case it is a good idea so that the radiator can do its' job properly. Any pipes running in unheated areas of the house should be insulated as well as possible. Remember that insulating central heating pipes in lofts can lead to frozen water tanks and water pipes if these are not insulated properly at the same time.
You can use either a digital thermometer or a non contact infra red thermometer (which is easier) to do this. See the Temperature Measurement Tips for more information on using these devices. Avoid the use of mechanical contact thermometers as these can have quite a long lag before they accurately reflect the pipe temperature.
To find out more about measuring how much heating oil you are using see the pages on measuring heating oil consumption. To help monitor oil use and cost JSutils has produced two heating oil calculators called EnCalcOL and EnCalcOU which work based on tank depth or volume readings and cope with different shape tanks. EnCalcOU calculates cost and use, EnCalcOL calculates use. Both can also predict oil use. To find out about measuring gas consumption see the measuring gas use page. To help monitor gas use JSutils has produced a gas use and cost calculator called EnCalcGU which works based on meter readings and can also predict gas use and cost. All of the programs are free for personal non commercial use.
As well as using oil or gas central heating systems also need electricity to run the pump, valves, time switch and control system. More information on these can be found in heating electricity use.
This is a method you can use to set up and balance the central heating system including the radiators and is applicable to the feed and return type of heating system (probably the most common) fueled by gas or oil.
It is quite likely to turn into an iterative process, so rather than trying to remember everything we have 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 temperatures and the difference several times. Last time we did this it took us 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, Try using 0 for fully closed and then count upwards in quarter turn increments as you open them. The record sheet to use can be found in the checklist Index . Before starting make sure you have all the tools needed to open valves and bleed radiators.
1. Record the 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. See the comments about stuck valves and valves which don't fully open on the thermostatic valve page.
4. Open all the flow control valves fully. Take note of how many turns between fully open and fully closed for each one.
5. Set any room thermostats to maximum.
6. Bleed all the radiators with the heating system off to ensure there is no air in them (plus any other bleed valves in the system - sometimes there are two in the loft, one on the feed and one on the return - usually in bungalows).
7. For pressurised systems reset the system pressure following the manufacturers instructions.
8. 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.
9. When the system has cooled down, turn on the boiler.
10. As the system warms up, go round the radiators and identify the flow and return connections (flow gets hot first).
11. Find which radiators are heating up the quickest by feeling them.
12. 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. Don't turn any valve off completely, for the hottest ones we suggest closing by no more than half way.
13. Let the system stabilise for a couple of hours.
14. 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).
15. 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.
16. Repeat 14 and 15 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).
17. Adjust the boiler to give a flow temperature of 80C measured on the boiler output pipe and the pump speed to give an average differential of 12C across all radiators.
18. If the pump speed is changed it may be necessary to repeat 14 and 15 until all the radiators are fully hot all over and the differentials are as close as you can get them to 12C.
19. Refit the covers to the flow control valves.
20. Where fitted set all thermostatic valves to achieve the desired temperature in each room. Do this over several days as rooms can take a long while to heat up and cool down,
21. If fitted set the room thermostat to give desired room temperatures (see confusion between room and radiator thermostats below).
22. 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 (see setting boiler thermostats below).
23. Measure the temperature of the flow and return pipes near to the boiler. Keep this information with the other records to aid fault finding in the future.
If a room thermostat is in a room with radiators fitted with thermostatic valves you will need to decide which is going to control room temperature, often the room thermostat will also turn off the heating to the whole house when its set temperature is reached. The best compromise if not all radiators have thermostatic valves is to set the thermostatic valves in the room with the thermostat for slightly higher than the desired room temperature and then the room thermostat to the desired room temperature. If all radiators have thermostatic valves it is not worth bothering setting the room thermostat if there is a time switch fitted, in this case set the room thermostat to its the maximum temperature, otherwise set it to the temperature required and the thermostatic valves in that room to the maximum temperature. Often room thermostats are in halls which means they can be subjected to drafts which can make the heating operate in a strange way, in this case either minimise the draughts or use the radiator thermostatic valves to control the room temperature.
The final setting of the boiler thermostat is always going to be a compromise, the lower the setting the longer the system will take to warm up and the higher the setting the more gas or oil will be used. With condensing boilers without intelligent boiler temperature control the maximum efficiency will be with the boiler return temperature below around 55C. The lower the losses in the system the harder this return temperature is to achieve.