Pipe and duct insulation plays an important role in modern buildings, helping to keep them operating efficiently and affordably. However, with building services coming in a range of sizes and serving a variety of different purposes, it can be difficult to know what thickness of insulation you need to fit. BS 5422 has been created to answer these questions, providing a reference point to allow you to find the thickness you need.
In this blog, we’ll explain how to use this standard document. However, if you just want to check the thickness of Kingspan pipe or duct insulation that you need, we provide calculated thickness tables in our brochures available online for standard conditions or via hvactechnical@kingspaninsulation.co.uk for specific conditions.
What is BS 5422?
BS 5422 is a British Standard developed to cover insulation applications on pipes, tanks, vessels ductwork and other equipment operating at temperatures between -40oC to +700oC. The document provides best practice guidance covering a range of issues around insulating building services including addressing condensation and fire risk. The core of the document, however, is a range of tables which provide minimum insulation thicknesses for a range of different systems and scenarios.
An example table is shown below. Whilst these can be confusing at first, by getting up to speed with a little insulation terminology you should be easily able to find the right thickness for your project.
Identifying the right table
BS 5422 offers minimum or indicative thickness for a wide range of different systems contained in 25 tables. It’s important to ensure you’re looking at the right table to start with. This is because the expected operating temperature can have a significant impact on the thickness of insulation you need. Systems which operate near to ambient temperatures will be less likely to suffer from heat transfer, either to or from the services. As a result, they will need less insulation than a system operating at very low or high temperatures.
Clause 4 of the standard identifies the specification information you may need to identify the correct table. These are outlined below:
a) system operating temperature;
b) design ambient air temperature;
c) relative humidity of the ambient air;
d) air velocity;
e) location of the plant (indoors or outdoors);
f) pipe diameter (or flat surface dimensions);
g) orientation of pipes (horizontal or vertical);
h) vertical dimensions of flat surfaces; and
i) emissivity of outer surface.
The importance of insulation thermal conductivity/lambda (λ)
The other key piece of information you need is the thermal conductivity or lambda of the insulation material. This is denoted with the symbol λ. The lower the lambda value of an insulation material, the more effective it is at preventing heat loss. This means it may be possible to fit a slimmer thickness of insulation without compromising on thermal performance.
In practice, there can be a good deal of variance in the thermal performance of materials used for lagging pipe and ductwork. For example, our Kooltherm Pipe Insulation can achieve aged thermal conductivities as low as 0.025 W/mK. By contrast, mineral fibre lagging typically only achieve thermal conductivities of 0.033 W/mK or worse. As we’ll see, this can have a significant impact on the thickness of pipe insulation that is needed.
All pipe insulation products should be supplied with clear information about their thermal conductivity. As this value is affected by the mean temperature of the insulation, this will typically be supplied as a curved graph. For example, below is the thermal conductivity curve for Kooltherm pipe insulation produced on our continuous production line. To find the correct mean insulation temperature for an application, you add the operating temperature of the system to the ambient temperature and then divide this value by 2; this produces a curved graph.
How to use the tables in BS 5422
Once you have identified the correct table within BS 5422 and know the thermal conductivity of the insulation product or products you are considering, you can then use the table to identify the thickness you need.
In this example, we’ll look at table 15 which covers pipe insulation for non‑domestic heating services to control heat loss – low emissivity outer surfaces.
In the left-column (in red), several standard pipework diameters are listed whilst along the top (in green) are the expected operating temperatures separated into three groups. As these each cover a range of operating temperatures, a single standardised temperature is used within the calculation (listed in the row below). Once you’ve matched these up you can then select the appropriate lambda value from the fourth row (in blue). As you can see, the higher the lambda, the greater the minimum thickness that is needed.
As the table only covers thermal conductivities in 0.005 WmK increments, the specific lambda for your chosen insulation may not be listed. Where this is the case, one option is to round up to the nearest number – this will ensure you definitely meet the minimum thickness requirements. Alternatively, many manufacturers provide tables with minimum thicknesses for their specific product which have been pre-calculated to ensure heat losses are below the max heat loss value (shown in yellow).
You can find the pre-calculated values for Kingspan products within our product literature – ensuring you can meet your project requirements with a minimum thickness of pipe or duct insulation.
