Insulating Central Heating And Hot Water Pipes
Any pipes for hot water and central heating running outside the heated areas of the house are potential sources of heat loss. It is worth having a look at all of these, checking for good quality insulation especially around joints and valves. Bear in mind that improving the insulation of these pipes should also include any adjacent cold water pipes since improving the insulation of hot pipes may make the cold ones more likely to freeze up in winter. It is not worth doing any work to insulate any hot pipes within the living area unless the heat from the pipes is making a room too warm and negating the effect of thermostatic radiator valves. Where pipes run between floors it is only worth insulating these if there are significant draughts around these pipes since the heat will tend to rise to contribute to heating the floor above, fixing the draughts will have a similar effect.
It is not sufficient to insulate the pipes with any old material or the cheaper types of foam pipe insulation (the thicker the better), it is worth investing in decent quality material since the extra cost is small and is outweighed by the gains especially on long pipe runs. Ideally the temperature drop from one end of a pipe to the other should be close to zero. A useful improvement can also be obtained by insulating pipes and then boxing them in wood (make sure valves are still accessible) which gives an insulating air gap. This technique is demonstrated by this before and after example of insulating central heating pipes.
Process Of Insulating Pipes
In order to evaluate what was needed to achieve a near zero temperature drop along a given pipe we measured the temperature drops at each end of a number of central heating pipes in the loft with the central heating stabilised. The longest run of approximately 30 feet (around 9 metres) originally had a drop of 12C (21.6F) - the the 15mm copper pipe was insulated along most of it's length with cheap foam insulation. Replacing the insulation with a more expensive foam reduced this to 6C (and made the radiator at the end hotter), Butting and taping all the joints carefully reduced this drop to 4C. Laying the loft insulation over the pipe instead of under it reduced the drop to 2C. A later improvement was to box the pipe run in cheap wood before laying the loft insulation over the top which reduced the temperature drop to around 1.5C. The location of the pipes made moving the loft insulation very simple. A block of foam was then cut up to insulate the two isolation valves (clearly marked with their function) giving a final drop of just over 1C. The same insulation methods were applied to most pipes in the loft totally unbalancing the central heating system which was re-balanced.. These changes also meant the boiler output temperature could be reduced hence achieving a useful energy saving.
Note that if a pipe is feeding a radiator with a thermostatic valve fitted the valve needs to fully open for at least an hour before measurements are taken (remember to reset it afterwards), otherwise some strange temperature readings will result. It is also important the heating system has stabilised. In practice the actual temperature drop depends not just on the insulation but also on the ambient temperature, the size of the radiator(s), the flow rate and the water temperature.
Measuring Pipe And Insulation Temperature
We have used both a digital thermometer (which needs time to stabilise) and a non contact infra red thermometer (which is easier to use and gives nearly instant results) to do this. See Temperature Measurement Tips for more information. Using the infra red thermometer it is also possible to measure the temperature of the outside of the insulation which is another useful guide to it's efficiency.