A gas cleaning installation, such as might be used to filter particulate material from exhaust gases of a power generating boiler or the like, which comprises a pair of gas cleaning chambers each containing filtration means for a gas stream passing through the installation. The chambers are spaced apart to define between them a gas inlet passage or passages into the underside of each chamber and, above, the inlet passage or passages a gas outlet passage or passages. The gas outlet passage or passages together include a portion extending at least part way across the upper end of each chamber, the outlet passage or passages communicating with each chamber through an aperture extending between the interior of the chamber and the interior of the respective portions of the gas outlet passage or passages.