Ventilation Page
Use this as a guide to entering data on the Ventilation page.
Ventilation Zones
A typical property will only have a single ventilation zone. However, if the property has two or more ventilation systems, they should be entered as multiple zones as long as there is no air movement between the zones.
Zone Information
Number of storeys
The heat loss due to infiltration is a factor of both the height of the building and the number of exposed & sheltered sides. Entering the number of storeys helps the Heat Load Calculator to determine the height of the building or ventilation zone.
Higher buildings with increased exposed facades will have more ventilation heat losses due to forced infiltration from exposure to the wind.
Number of external facades
External facades are the sides of a building that are not attached to another property or building. The number is determined automatically by the attachment type of the dwelling, based on these default values:
| Dwelling Type | Attachment | Number of External Facades |
|---|---|---|
| All | Detached | 4 |
| All | Semi-Detached | 3 |
| All | Mid-Terrace | 2 |
| All | End-Terrace | 3 |
| Flats/maisonettes | Enclosed Mid-Terrace | 1 |
| Flats/maisonettes | Enclosed End-Terrace | 2 |
Number of sheltered sides
Sheltered sides are the facades of a building that are shielded or protected from the wind by adjacent buildings, trees or tree-height hedges.
A side is considered sheltered if it is effectively obstructed from the wind and all of the following apply:
- the obstacle providing the shelter is at least as high as the ceiling of the uppermost storey of the dwelling
- the distance between the obstacle and the dwelling is less than five times the height of the obstacle
- the width of the obstacle (or the combined width of several obstacles) is such that it subtends an angle of at least 60° within the central 90° when viewed from the middle of the wall of the dwelling that faces the obstacle
For instance, a detached property in a rural environment may have no sheltered sides, whereas the same property in an urban area may have four sheltered sides if it is surrounded by other buildings.
Attached Properties
In the case of attached properties, party walls would always be considered a sheltered side.
NOTE
For more detailed information on how to determine sheltered sides, please refer to Standard Assessment Procedure (10.2) Section 2.5.
Base height above ground
For flats/apartments or where multiple ventilation zones exist, you can also specify the base height (in metres) of the zone above ground level. This helps determine whether any additional infiltration is required due to the wind exposure at higher levels.
Ventilation Type
The ventilation type determines the way in which fresh air is supplied to the ventilation zone. Unless a mechanical ventilation system is clearly identified during a property survey, the building is likely to be naturally ventilated.
Intermittent Extract Fans
The ventilation type refers to how entire property is ventilated, not individual rooms. Intermittent extract fans within rooms DO NOT constitute mechanical ventilation. They should be entered as Natural Ventilation but with ventilation devices added within any relevant rooms.
Natural Ventilation
A property is naturally ventilated if fresh air is supplied through the opening of windows/doors and through trickle vents above windows.
Mechanical Ventilation (MV) and Mechanical Extract Ventilation (MEV)
These are whole-house fan-assisted mechanical ventilation systems that can be either unbalanced (extract-only) or balanced (supply and extract).
Mechanical Ventilation with Heat Recovery (MVHR)
MVHR if a form of whole-house mechanical ventilation that incorporates a heat exchanger to recover warm air before it is extracted from the property.
When using this option, a heat recovery efficiency percentage must be entered as well. This would typically be obtained from manufacturer data.
Positive Input Ventilation (PIV)
PIV are whole-house ventilation systems that supply air into the property from a central location. They create a slight positive pressure within the property, forcing stale air out through gaps and cracks in the building fabric.
NOTE
For default supply and extract ventilation rates for mechanical systems, see Ventilation Rates.