Flue restrictor

A flue restrictor to control air flow in a combustion apparatus to burn oil or gas and having an exhaust system that includes a flue, the restrictor comprising:

• a housing to be attached in the flue and comprising a first sub-housing and a second sub-housing having continuous, imperforate side walls;
• a first valve member fixed at an end of the first sub-housing;
• a second valve member fixed at an end of the second sub-housing, each valve member comprising a plate having a central opening within an inner ring with discrete fins extending outwardly from the inner ring and spaces between each fin;
• the first and second sub-housings being positioned with the first and second valve members located against each other with the central openings of the valve members aligned, the valve members cooperating with each other to act as a valve, the sub-housings being rotatable relative to each other between a closed position of the valve where the fins of one valve member align with the spaces of the other valve member to an open position where the spaces of each valve member align;
• means to lock the sub-housings in a predetermined relative position to control air flow in the restrictor and thus in the combustion apparatus;
• the central openings in each valve member being so dimensioned that when the valve is closed the flow through the aligned central openings is about 30% of the flow through the unrestricted flue;
• and
• the sub-housings being enlarged relative to the flue so that when the valve is opened flow through the restrictor is the same as flow through the unrestricted flue.