What are Closed Flues?
Dominic Bowkett
Last Update 13 hours ago
Within the revised ventilation section of RdSAP 10, as clarified by Convention 9.01 and supporting guidance, closed flues are specifically defined as chimneys or flues that are attached to a wood or solid fuel stove/appliance with controlled air supply. For example, a log burner or a coal stove with doors.
This distinction is crucial for qualified assessors. Unlike open chimneys or open flues, which are open to the atmosphere that contribute significantly to air leakage and heat loss, an appliance with a controlled air supply system is designed to contain the combustion process more effectively, with the flue primarily serving as an exhaust for combustion gases.
Key Aspects for Assessors when Recording Closed Flues:
Definition: The fundamental characteristic is the connection to an appliance which has doors. This implies a sealed combustion chamber where air for combustion is typically supplied directly to the appliance, and combustion products are expelled through the flue without significant interaction with the room's air.
Differentiation: Assessors must carefully differentiate closed flues from other flue types. A closed flue will only be attached to a solid fuel burning appliance which has doors, where as other "flues" are defined as having a vertical duct of up to 200mm in diameter and are attached to either solid fuel boilers, open fireplaces with no heating appliances, or gas room heaters. Read our other articles for how to identify each type of flue.
Ventilation Impact: While a closed flue's primary role is exhaust, its presence and type contribute to the overall ventilation strategy modelled by RdSAP. The system's design inherently influences the dwelling's air tightness and the rate at which air is exchanged.
Documentation: As with all elements of an energy assessment, thorough documentation is essential. Assessors should visually confirm the presence of a closed fire and its attached flue, ensuring that the classification aligns with the definitions provided in the RdSAP 10 conventions.
By meticulously identifying and accurately recording closed flues, along with other ventilation elements, qualified assessors ensure that the energy assessment provides a robust and reliable reflection of the property's energy performance, adhering to the updated standards of RdSAP 10.