Is often referred to as MEV or Mechanical Extract Ventilation, it works by removing contaminated air from the ‘wet rooms’ – bathrooms, kitchens, utility rooms – and replaces it with fresh air from trickle vents, together with air leakage in the habitable rooms.
PROS: Easy to install, low level continuous background ventilation with boost facility, only one power supply needed and one external penetration, cheap to install
CONS: Requires trickle vents in windows, wastes heat, creates draughts,
In ‘PIV’, tempered fresh air is gently introduced from the loft by a single fan unit through a ceiling diffuser mounted over the landing (or hallway, in a single storey dwelling). This filtered air creates a slight positive pressure, reversing the normal airflow and forcing stale air out the building. The incoming air collects any residual heat from the loft and redistributes heat that naturally accumulates at the top of the stairs.
Consists of a number of individual extract fans and background ventilators running continuously at a low trickle speeds designed to boost as required.
PROS: Easy to install, low level continuous background ventilation with boost facility
CONS: No trickle vents, wastes heat, creates draughts,
This form of ventilation is the most commonplace in the UK.If you are currently working to Building Regulations that do not insist on a System 4 ventilation system (i.e heat recovery ventilation) or you are simply looking to ventilate one room then you may be considering installing extract fans and trickle vents in your property.
PROS: simple to install, and operate, remove pollutants quickly
CONS: Require trickle vents in windows, wastes heat, noisy, creates draughts, limited product life,