Variable orifice restriction device

A variable orifice restrictor for an air induction system of a gas fired boiler, the variable orifice restrictor comprising:

• a ducting box having a box body, a box body housing mounting inlet, and a box outlet;
• a housing having a seat, a housing inlet, and a housing outlet, the housing inserted via the box body housing mounting inlet and attached to the ducting box;
• and
• a flap assembly comprising a flap cover and a flap pivot, the flap assembly hingedly attached to the housing and closed by a holding force from a weight directly attached to the flap cover with a weight fastener at a discrete position on the flap cover, wherein the weight is shaped and configured to span a portion of the width of the flap cover and a location of the weight is configured to vary from a first discrete position on the flap cover to a second discrete position on the flap cover, wherein the flap assembly is configured to rotate in response to a pressure differential between the ducting box and the housing that is sufficient to overcome the holding force, and the flap assembly further including a limiter provided in the form of a screen coupled to the ducting box to limit rotation of the flap assembly,
• wherein the variable orifice restrictor provides a turndown ratio of an air flow rate through the air induction system via the flap assembly, the housing, and the ducting box.