HVAC legislation

HVAC Legislation

Part L of the Building Regulations describes the minimum provisions for the insulation of pipes and ducts serving space heating, hot water, chilled water and ventilation systems, in both new build and existing properties. This includes gas, oil and solid fuel systems, as well as solar, electric and community or district heating schemes.

With new installations in dwellings pipes should as set out in the four following instances - be encased with insulation that complies with the Domestic Heating Compliance Guide, while taking into consideration the permissible heat loss, and labelled accordingly:

  • Primary circulation pipes for heating and hot water circuits should be insulated wherever they pass outside the heated living space, or through voids which communicate with, and are ventilated from, unheated spaces.
  • Primary circulation pipes for domestic hot water circuits should be insulated throughout their length, subject to only practical constraints imposed by the need to penetrate joists and other structural elements.
  • All pipes connected to hot water vessels, including the vent pipe, should be insulated for at least one metre from their points of connection to the cylinder or they should be insulated up to the point where they become concealed.
  • If secondary circulation, such as a pumped circuit feeding bath and basin taps in a large property - is utilised, all pipes fed with hot water should be insulated.

For replacement systems, meanwhile, such as when a boiler or hot water storage tank is changed, any pipes as mentioned in the four situations above that are exposed as part of the work, or are otherwise accessible, should be insulated and then labelled in line with the requirements of the Domestic Heating Compliance Guide. If there are practical constraints, then it is acceptable to use a lesser standard.

In assessing the thickness of insulation required, compliance calculations are based on a horizontal pipe carrying an input temperature of 60oC, situated in still air at 15oC ambient. To provide a couple of examples, this would mean that a pipe diameter of 8mm is allowed a maximum heat loss of 7.06 W/m, while the largest diameter of 54mm would require heat loss of no more than 14.12 W/m.

Insulation for pipework in unheated areas is treated differently, however, and extra provision may need to be made to protect central heating and hot water pipework from freezing, for which guidance can be found in BS 5422:2001*,which offers methods for specifying thermal insulation materials for pipes, tanks, ductwork, vessels and equipment operating in temperatures between -40oC and +700oC.

For buildings other than dwellings, the insulation of pipework and ducting is, again, essential to minimise heat loss for heated systems, and heat gain for cooled systems. Here, hot water and heating pipework should be insulated in all areas outside the heated building envelope, but additionally, this includes voids, as well heated spaces that may vary in temperature compared to other zones within the building. Simply put, this means that control is maximised to ensure that heat loss from uninsulated pipes should only be permitted where the heat can be demonstrated as being ‘always useful’; which could include protecting against damp or condensation. As with dwellings, there are maximum permissible heat losses for different sized piping.

Cooled or chilled pipework, by contrast, should be insulated along its whole length in order to limit heat gain. The guiding principles here are that heat gain to uninsulated pipes should only be permitted where the proportion of the cooling load relating to distribution pipework is proven to be less than 5% of the total load.

Hot and cold air ducting should also be insulated along its whole length but, where it is used for both chilling and heating, the provision for chilled ducting should be adopted.

The Climate Change agenda and the planet’s dwindling reserves of fossil fuels require us to adopt a holistic strategy to energy conservation. Accordingly, consultants and contractors are also obliged to respect BS 5970:1992: the Code of Practice giving recommendations for the specification and installation of insulation.

It directs that thermal insulation materials used should be manufactured and tested under an approved ISO- 9002 Quality Management System and comply with the relevant British Standard specification; if available. They should be suitable for continuous use without degradation throughout the range of operating temperatures and must provide proof against rotting, mould, fungal growth and attack by vermin. Products employing CFCs in their manufacture should not be used.

*Although BS 5422:2001 (Method for specifying thermal insulating materials for pipes, tanks, vessels, ductwork and equipment operating within the temperature range -40oC to +700oC) has been replaced by the Thermal Insulation Manufacturers and Suppliers Association (TIMSA) Guide, it is still the main reference document for compliance with Technical Handbooks Section 6 in Scotland and Technical Guidance Document L to the Building Regulations in the Republic of Ireland.

The considerations in this publication that need to be taken into account is the application of the ductwork, is it handling warm or chilled air; the temperature difference between the air inside the ductwork and ambient air, or the minimum air temperatures, inside the ductwork; and the thermal conductivity of the insulation being used at the mean operating temperature.

With the above data, it is then possible to use the tables provided to determine the thickness of insulation required to meet the standard. 

Different requirements apply to England, Wales, Scotland and NI.

Background information on the domestic and non-domestic compliance guides for England can be found here: