Insulating
Central Heating And Hot Water Pipes
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General Information
Any pipes for hot water and
central heating running outside the heated area 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. Where pipes run between floors it is ony 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
In order to evaluate what was needed to achieve a near zero temperature
drop along a given pipe I 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 8 metres) originally had a drop of 12C (21.6F)
- the 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 isolation valve (clearly marked with
it's function) giving a final drop of just over 1C. The same insulation
methods was applied to most pipes in the loft totally
unbalancing the central heating system which was rebalanced.
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 while
measurements are taken (remember to reset it afterwards), otherwise
some strange temperature readings will result. It is also important
the heating has stabilised. In practice the actual temperature
drop depends not just on the insulation but also on the ambient
temperature, the flow rate and the water temperature.
Measuring Temperature
I 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.
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