A damper, damper kit and method are for installing a damper in a duct defining a gas conduit. The damper kit includes a first aperture closing unit engageable with at least one conduit wall and configured to close a first aperture when engaged therewith and including a shaft receiving section opened in the gas conduit. The damper kit has a second aperture closing unit engageable with the at least one conduit wall and including a shaft receiving section opened in the gas conduit. The damper kit includes a damper having at least one shaft with a first section insertable in the shaft receiving section of the first aperture closing unit and a second section insertable in the shaft receiving section of the second aperture closing unit and extending past the at least one conduit wall through the second aperture closing unit.