Flue gas systems are subject to the effects of the weather and to the operation of the heat generator, so updraft conditions (a chimney's 'pull') are changing all the time.
Constant conditions are essential for consistent combustion quality and a high degree of utilisation however. This applies not just to new flue systems but is equally true when a modern heat generator is connected to existing chimneys.

Rising energy prices coupled with a dwindling supply of raw materials make it essential to use precious resources sparingly. Consistent combustion under optimum operating conditions is a solution to this challenge.
Draft regulators of the type supplied by Kutzner + Weber match the flue system within given limits to the heat generator and its operating mode, and improve the dewpoint response of the flue system.

Draft regulators ensure:

• A constant updraft inside the flue
• Improved starting response for blower burners
• That existing flue systems are matched to the performance and operating mode of a new boiler
• That the flue system is ventilated to prevent the formation of moisture during breaks in boiler operation, with a positively controlled or combined draft regulator being particularly effective.

Draft regulators from Kutzner + Weber comply with DIN 4795 and are manufactured under controlled quality.
Their function is based on the differential pressures in the installation room and the chimney. While the pressure in the installation room is virtually the same as the outside air pressure, a negative pressure is present in the chimney. If this negative pressure rises above the draft restrictor setting, the regulator damper is opened and secondary air can enter the chimney. Air is only added until the chimney pull has reached the minimum draft that is required.

Draft restrictors work on the "weighing scale" principle. At the regulator damper of the draft restrictor there is equilibrium between the opening forces exerted by the chimney updraft and the closing forces from the balancing and setting weights.

• The flue gas temperature and the thermal updraft decrease
• The flue gas volume and flow resistances increase
• The dewpoint of the flue gas volume falls, more or less offsetting the lower mixture temperature
• The flow velocity rises, thus reducing the dwell time in the flue system (reduced cooling down)

1. Self-acting draft regulator (draft restrictor):
   The aperture is opened as a function of a differential pressure, allowing secondary air to enter the chimney to maintain a constant 'pull'.
2. Positively-operated draft regulator:
   During the times when the appliance is idle, a motorised control system opens an aperture to allow secondary air to enter the chimney for ventilation purposes.
3. Combined draft regulator:
   This type combines the function of a draft restrictor with that of a positively controlled draft regulator, guaranteeing both a constant flue updraft and ventilation.
4. Draft regulators for positive pressure flue systems:
   Flue systems that are designed to operate with positive pressure can enter the negative pressure range on cold and/or windy days and at high altitudes. Too much negative pressure can cause malfunctions, especially during part-load operation.

This problem can be resolved by a motorised, pressure-switch controlled draft restrictor ZDM 180, which can be configured to function as a combined draft regulator in addition to ventilating the flue system, and as a starting aid for the burner.

The most effective position for this restrictor will depend on the geometry of the interconnecting pipe and on the flue system itself. Potential mounting options are the connector piece immediately after the flue gas socket or just before the inlet, as well as in the wall of the flue system above or below the connector piece.

Installing a draft regulator ensures the best possible operating conditions for the appliance. As well as saving energy, draft regulators promote the longevity of the flue system.