Hovelling

It would, perhaps, be proper to make the drain-flue distinct from the chimney-flues where it opens out above, so long as the defective ventilation of buildings in other respects renders the chimney-flue of an apartment the only means of access to it of the outer air when the doors and windows are all shut, or the foul air brought up by the drain-flue may be caught up by the down-draught of its neighbour chimney-flue. The hovelling of the drain-flue would go far, however, to prevent any such consequence as that last alluded to, whilst the application to any such flue of a tube or cowl of almost any kind will check down-draught.