One type of smoking chimney is known as downdraught and is caused when air is blown back down the chimney. Typically this will result in puffs of smoke coming out of the stove or fireplace. Sometimes it is possible to incorrectly identify a smoking chimney problem as downdraught when in fact it is not. If the smoke is continuously coming out of them this is not downdraught - please see other causes of a smoking chimney on the smoking stove or fireplace page. Downdraught is typically caused by a chimney that is either not high enough or where there are high buildings or trees nearby that affect the wind currents around the chimnney. Often downdraught will only occur in certain conditions so you might find that it is only on days when the wind comes out of the North that the stove smokes in puffs because of downdraught.
Often raising the height of the chimney is the simplest solution to downdraught. With a double skin insulated chimney this can be done by attaching another length, with a masonry chimney you either have to extend the brick/block courses or you might consider adding a taller chimney pot.
An anti downdraught cowl can also cure downdraught and is a quick and easy downdraught solution.
A Rotorvent cowl is designed to improve draw when there is wind to turn it - generally we prefer the MAD anti-downdraught cowl to the rotor vent as it consistently stops downdraught. A rotorvent cowl can also become clogged up with deposits if it is not cleaned regularly and so actually inhibit draw.