System 1 – Requires trickle vents in all rooms with external walls, with intermittent fans in all wet rooms.
- Low price, cost effective.
- High heat loss.
System 3 – Trickle vents in all habitable rooms, with a centralised unit extracting from all wet rooms to outside, or decentralised units in each wet room.
- Flexible, either one air pathway through building, or multiple units to avoid ducting issues.
- Continuous extract, for constant air renewal.
- Can be more expensive than System 1.
- Heat loss through trickle vents.
System 4 – Requires heat recovery unit, with no trickle vents within dwelling. Ducting will be required for extract system from all wet rooms to atmosphere. Ducting will be required from atmosphere (outside of building) to habitable rooms.
- Heat recovered from habitable rooms reduces heating costs.
- Suitable for more air tight houses.
- Gives a controlled air path through dwellings.
- More expensive than both system 1 and 3.
- Need space for heat recovery unit and ductwork to be run through the house.
- System will need to be installed and commissioned by a qualified engineer.