Ventilation: Approved Document F, Volume 1 — Dwellings

O N L I N E V E R S I O N F1(1) 1.70 For dwellings using mechanical ventilation with heat recovery, each wet room should have a minimum continuous mechanical extract ventilation high rate as given in Table 1.2. 1.71 Mechanical ventilation with heat recovery systems should be designed to avoid the moist air from the wet rooms recirculating to the habitable rooms. Background ventilators 1.72 To avoid unintended air pathways, background ventilators should not be installed with mechanical ventilation with heat recovery. Purge ventilation 1.73 For purge ventilation follow paragraphs 1.26 to 1.31. NOTE: The efficiency of mechanical ventilation with heat recovery systems should improve as the dwelling becomes more airtight. Installation of ventilation systems 1.74 Ventilation systems should be installed to meet both of the following conditions. a. Comply with the guidance in this approved document. b. Not compromise the performance of the system. 1.75 Adequate space should be available for access to maintain ventilation equipment. 1.76 Rigid ducts should be used wherever possible. 1.77 Flexible ductwork, where installed, should meet all of the following conditions. a. Only used for final connections. b. Lengths should be a maximum of 1.5m. c. Meet the standards of BSRIA’s BG 43/2013. 1.78 Any flexible ducts should be installed so that the full internal diameter is maintained and flow resistance is minimised. This is achieved by taking both of the following actions. a. Pulling the duct taut. b. Ensuring that ductwork does not pass through orifices with a smaller diameter than the duct itself. 1.79 Ductwork installations should be designed and installed to minimise the overall pressure losses within the system by taking all of the following steps. a. Minimising the overall length of duct. b. Minimising the number of bends required. c. Installing appropriately sized ducts for the air flow rate. 1.80 Each air terminal should have a free area of at least 90% of the free area of its associated duct. 17 Building Regulations 2010 Approved Document F Volume 1, 2021 edition O N L I N E V E R S I O N