DRAFT CONTROLS

WHEN TO USE A DRAFT CONTROL:

 
DRAFT INDUCERS/POWER VENTERS
With these devices, draft is increased or created causing fluctuations in air flow through the combustion chamber. These fluctuations can be negated by the use of a barometric draft control located between the draft inducer or power venter and the furnace, boiler or water heater it services.
Use a single acting control for oil and gas fired equipment with a power vented system. A single acting control for oil and a double acting for gas fired equipment with a draft control induced system.
POWER BURNERS
A power burner is designed so that a fan delivers positive air flow to the combustion chamber. A single acting draft control for oil regulates the over-the-fire draft. A power burner designed to burn natural or LP gas operates in the same manner. While a draft hood (diverter) is often used on gas units fired with an atmospheric burner, a double-acting barometric draft control should be used for furnaces or boilers fired with gas power burners.

FORCED DRAFT BURNERS
Forced Draft installed with a stack height in excess of 30' will probably develop excessive natural draft, reducing the amount of pressure within the furnace or boiler. A barometric draft control will help eliminate this undesirable stack action and permit the unit to be pressurized.

DUAL FUEL APPLIANCES
Burners capable of burning either gaseous fuels or oil should be equipped with a barometric draft control. We suggest using a double-acting control on units where fuels are frequently changed. The double-acting feature is important for gas firing appliances, it allows spillage of combustion products in case of blocked flues or down-drafts. To detect flue gas spillage on dual fuel installation, a Field Thermal Switch is recommended.

GAS FIRED APPLIANCES
Gas fired furnaces and boilers generally require a double acting draft control. Like a single-acting control it opens inwardly to maintain a uniform draft. But, unlike a single acting control, it is also free to open outwardly to spill the products of combustion in case of blocked flues or downdrafts.
National codes often mandate the use of a draft hood. Usage is generally limited to furnaces or boilers designed for use with power burners and incinerators. Draft controls are generally used when oil fired units are converted to gas.

HOW DRAFT CONTROLS WORK:
Static pressure of the cool air (1) exerts pressure on the outside of the furnace or boiler, the breeching and stack. The pressure difference between the room air and heated gas (air) causes products of combustion (2) to flow (draft) through the unit and rise through the breeching and chimney.

Room temperature air (3) enters through the barometric draft control (4) in the precise amount needed to overcome the excess drafts caused by temperature variations, wind fluctuations and barometric pressure changes.

Combustion of fuel is complete and the process is stabilized. The velocity of combustion gases through the heat exchanger is slowed so more heat is extracted. The unit operates more efficiently, reliably and requires less maintenance.