If you are lagging the pipe to prevent it from freezing then unfortunately this will not work. Insulating the pipe will only delay the action of freezing. The only way to offer your customer 100% insurance gainst the pipe from freezing is to install trace heating combined with insulation. I have been in this business since 1968 and believe me that is the only solutio. Should you only lag (insulate) the pipe, I would be more worried about the pipe freezing and the reaction from your customer.
A self regulating heating system is used as a solution to this problem due to its ease of installation, safety and lowest running cost. Kits are designed specifically for frost protection of pipework in the domestic / residential sector, especially boiler condensate dischrge lines.
The last two winters have really given a new meaning to the prevention of frozen pipes. Each year most industrial and commercial buildings generally take precautions to protect exposed pipework, but with unpredictable winters it has opened up a domestic market with a real need for frozen pipe prevention.
Key engineering features to look for in your pipe frost protection kit are very important and some of these are listed below:
1)The In-Line thermostat must be fully weatherproof and rated IP67 - it should operate by sensing air temperature and not by sensing at a single position on the pipe itself, thereby ensuring maximum protection is achieved at all times.
2)Assuming the maximum pipe size to be 32mm, the kit must provide frost protection at the lowest temperatures recorded during Winter 2010 – Look for self regulating rated at 12 w/m @ 10ºC and the recommendation to install in a straight run on the pipe and then install a minimum 13mm thickness of thermal insulation after fitting the trace heating. The heat loss calculation should be based on IEC 62395, the Standard for Electrical Resistance Trace Heating Systems for Industrial and Commercial applications
3)The flexibility of the heating cable must assist the installer, simplifying handling on site and providing ease of installation – this is particularly important when the installer has to fit the self regulating cable in a loop on the pipe within the wall
4)The small cross section (geometry) of the self regulating heating cable should allow the thermal insulation to fit comfortably and keep the aesthetics of the installation to a good standard and acceptable to the property owner.
5)The kit must include a spare end cap to enable the length of self regulating heating cable to be cut to the exact length of the pipe and sealed
6)In-line junction box in the kit must be complete with cable retention clamps to EN-60598-1 & BS4533 for increased safety
Hope the above helps