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​​​​​Thermal FAQ: pipe freezing.​

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 TI: Pipe Freezing

FAQ Pipe Freezing​.


 

What thickness of insulation will prevent pipe freezing?

If water remains stationary within a pipe and the ambient temperature remains below the freezing temperature (0 °C) indefinitely then eventually the water will freeze. This will occur regardless of the thickness of insulation applied.

Insulation of pipework does however offset the time before freezing occurs. If freezing can be offset by 12 hours or more (lasting through a whole evening in the Winter) then it is unlikely the pipe will ever freeze.


 

What insulation thickness’s do the water regulations recommend?

UK water regulations identify 2 scenarios: “normal conditions” and “extreme conditions”. Normal conditions are taken as pipework within the building fabric but in areas which are normally unheated - such as cloak rooms, loft spaces, garages etc. Under normal conditions pipework is expected to resist freezing for a minimum of 12 hours at -6 °C.

The thicknesses of Kaiflex ST Class O needed to achieve this are as follows: ​

​Pipe O.D.
mm

​Pipe N.B.
mm

​Thickness
mm

​15​13.6​25*
​22​20.2​19
​28​26.2​9
​35​32.6​9
​42​39.6​9
​54​51.6​9

*Note on 15 mm pipe and smaller the thicknesses of insulation required to offset freezing by 12 hours are so great as to be impractical. Water regulations advice is to apply the largest thickness available - even though this will not provide 12 hours protection.


 

Why are thicknesses larger on small bore pipe?

Smaller pipes carry a much smaller volume of water and since the dominant factor when calculating freezing times is the thermal mass of water contained within pipework small pipes freeze much more quickly.

The principle underlying this is the same as that which causes streams and puddles to freeze overnight during the winter whilst rivers and lakes require freezing temperatures to persist for several days before freezing occurs


 

How can I prevent freezing if the temperature stays below freezing for several days/weeks?

Since the insulation only delays the time before freezing occurs, if the temperature is expected to remain below freezing indefinitely and the water in the pipe will be stationary for all of that time insulation alone will not be able to prevent pipe freezing.

The most reliable approach to preventing pipe freezing in this circumstance is to drain the system of water when not in use. An alternative approach would be to ensure a regular flow of water through the system.

A third approach would be to apply insulation in conjunction with self-regulating trace heating cable and this is preferred as the most practical option for many serious commercial applications.


 

What thickness of insulation should I use with trace heating cable?

To determine this calculate the likely heat loss from the pipe at the minimum temperature anticipated - the result should be given in W/m. If this heat loss is less than the Wattage rating of the trace heating cable then the trace heating cable will be able to keep the pipe at a constant temperature.

If the heat loss is greater than the Wattage rating of the trace heating cable then the thickness of insulation should be increased.


 

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