In which type of connectors are manual dampers allowed?

Manual dampers are specifically permitted with solid fuel-burning appliances because they are designed to help control the flow of combustion air and exhaust gases. These appliances often require more precise management of airflow to maintain combustion efficiency, improve heating performance, and reduce emissions of pollutants. The use of a manual damper allows the operator to adjust the airflow according to the specific burning conditions or needs of the system, providing greater control over the combustion process.

In contrast, gas-burning and electric appliances typically rely on automatic controls and safety mechanisms to regulate airflow and combustion, making the need for manual dampers less relevant or necessary. Dual fuel appliances, which can operate on either gas or solid fuel, also follow the guidelines relevant to the fuel type being used, meaning they do not primarily utilize manual dampers for operation. Thus, the application of manual dampers is not as applicable in those contexts.