Draft-assisting chamber

A generally vertical chamber adapted to be positioned proximate of the combustion gas exhaust port of a heating appliance and of the flue pipe attached to the heating appliance and to be in flow communication with both the exhaust port and the flue pipe, the horizontal cross-section of the chamber at all vertical positions having a mean area at least approximately four times the area of the exhaust port, the roof of the chamber being above the exhaust port of the heating appliance such that exhaust gas from the heating appliance flows generally laterally into the upper portion of the chamber, the flue pipe being connected to the chamber at a position above the exhaust port of the heating appliance, the chamber extending downwardly from the exhaust port a substantial portion of the height of the heating appliance, the inside of the chamber being in flow communication with ambient air outside of the heating appliance through at least one aperture proximate of the bottom of the chamber, whereby the initial exhaust gases leaving the heating appliance through the exhaust port after start-up of the heating appliance and prior to a sufficient draft being created in the flue pipe are collected in the chamber, those exhaust gases spreading in a downward direction in the chamber until such time as their buoyancy creates the steady-state draft in the flue pipe, the height of the chamber being sufficient to provide such buoyancy and the volume of the chamber being sufficient to accommodate such temporary collection of exhaust gases, and an exhaust gas sensor positioned within the chamber a selective distance above the said at least one aperture proximate the bottom of the chamber, the exhaust gas sensor creating a human detectable alarm when exhaust gases have spread downwardly in the chamber a sufficient distance to contact the sensor.