The rising cost of energy is increasing awareness of the need for effective insulation on domestic heating and hot water pipework and storage cylinders to help minimise heat losses.

The focus on such insulation is about to intensify due to the proposals in the Future Homes Standard to reduce the operational carbon emissions of new homes by at least 75% by 2025, compared with homes built to current Building Regulations. 

What’s more, the government has said that it will require homes built from 2025 to be ‘zero carbon-ready’, which means they will have to meet a zero carbon standard without the need for further energy efficiency measures.

In England and Wales, Approved Document L Volume 1: Dwellings (AD L1) provides brief guidance on the minimum thickness of pipework insulation for low temperature hot water space heating applications, as well as for domestic hot water services in new buildings and new installations in existing buildings. 

Table 4.4 in the latest (2023) edition of AD L1 gives the minimum thicknesses of pipework insulation for hot water services and space heating applications using “high performance insulation”. In this instance, high performance is defined as insulation with a thermal conductivity of 0.025W/(m.K) or better. 

In that table, minimum insulation thicknesses progressively increase from 5mm for microbore pipes with an internal diameter of 10mm or less, up to 20mm of insulation for pipes with an internal diameter of 100mm. If another insulation material (ie. not “high performance” as referenced in the standard) is used, then a greater thickness will be required and contractors should consult with the product supplier or manufacturer to check what products are appropriate.

For new domestic installations, the Building Regulations require all of the following pipework to be insulated:

  • Primary circulation pipes for heating and hot water circuits when they pass outside the heated living space, including where pipework passes through voids
  • All primary circulation pipes for domestic hot water 
  • All pipes that connect to hot water storage vessels, such as hot water cylinders and some heat interface units, for at least 1m from the point at which they connect to the vessel
  • All secondary pipework, such as a pumped circuit feeding bath and basin taps in a large property.

For replacement systems, AD L1 only requires any accessible pipes in the dwelling to be insulated.

In terms of insulation performance, AD L1 requires heat losses from insulated pipework not to exceed the limits outlined in pipework insulation standard BS 5422. Fortunately, the insulation thicknesses given in Table 4.4 satisfy the performance requirements of BS 5422.

Interestingly, given the increased use of heat pumps with their lower circuit temperatures (typically 45° and return temperature of 40°) and potentially lower heat losses, AD L1 says that heat loss calculations from insulated pipework should be based on a water temperature of 60°, “regardless of the actual design temperature”.

It should be remembered that the properties of the insulating material can affect its effectiveness. The k-value (sometimes referred to as lambda-value) is a measure of the thermal conductivity of a material, or how easily heat passes across it. K-values are determined through laboratory testing and can be used to easily compare the performance of different materials.

Installers should be aware that an updated version of BS 5422 is expected imminently. This is likely to incorporate changes to the method used to calculate insulation thickness, defined in the standard ISO 12241:2022.  Insulation manufacturers are expected to reflect the changes to the standard in their product data.

In addition to minimising heat losses from pipework, installers must ensure that incoming services do not increase a dwelling’s heat losses by compromising its airtightness. As such, AD L1 requires that grommets or flexible collars to be used around incoming services are sealed to the air barrier with air-sealing tape or sealant. 
Similarly, where internal services penetrate an air barrier and/or membranes “careful detailing should be used to achieve a robust and durable seal”.