Duct Heaters

Duct Heaters

When referring to duct heaters the general idea is a heavy duty modular unit installed in the ventilating ductwork of commercial, residential and institutional HVAC systems, although smaller "duct"  heating elements are used in the forced air heating systems of vehicles. Duct heaters can be complementary to a central heating system that utilizes forced air heating, also known as forced circulation heating or convection heating, where air is the medium that transfers heat.

Fans and blowers are integral to the transfer of heat, as their motion conveys the air through the duct heater, being warmed by the electric heating elements, and moved on through the ducting to the appropriate return or departure vents. Duct heaters work with existing central forced-air heating systems to preheat fresh air or returned air. The central air handler filters the air, re-heats it and blows it through the ductwork, where duct heaters strategically act as air temperature boosters. The conditioned air is distributed throughout the building then is returned to the central air handling unit (AHU).

Electric heater manufacturers generally construct duct heaters in rectangular or square box configurations but can create rounded ones for the best fit in certain sheet metal ductwork. Consisting of two major components, the heating elements and the electric terminal within the boxed framework, duct heaters can be bottom mounted, flange mounted, round collar mounted or slip-in and are easily installed in existing or new HVAC systems, with the heater control panel mounted in any convenient location.

The two types of heating elements used in duct heaters are open coil and tubular (standard and finned), each offering certain advantages. Open coil elements are coils of nickel chrome wire that are very popular due to excellent heat dissipation; however, tubular elements are more suited to demanding environments as they are sheathed with protective covers of metals such as aluminum, iron, stainless steel or steel. Because of their sheath, tubular elements are slower to respond but can hold up to humid and dusty atmospheres, and fins are used to help more quickly dissipate the heat. Sheathed elements, especially finned ones, offer a very long life with less maintenance and lower risk of fire and electric shock. For sheath material, keep in mind that stainless steel's heat transfer rate is much less than steel's, though stainless is used in corrosion resistant applications.

Choosing the right heating element, electrical components and controls is essential to get the most economy and efficiency from a duct heater. Temperature sensing duct heaters can be encoded to regulate electric heat output based on a desired temperature, and modulating controllers can allow successful duct heater operation in even extremely low air flow. Plus, electronic enclosures act as moisture/debris resistant and explosion proof housings.

Duct heaters provide that boost of extra heat needed for many applications. Besides HVAC systems, other uses include industrial dryer and oven atmospheres, drying rooms and fruit and produce ripening rooms, annealing and dehumidification processes, modifying air temperature for air to air heat exchangers, cryogenic exhaust gas heating, and providing a boost/backup for ground source heat pumps. Highly versatile with virtually endless combinations of heating element sizes and energy capacities, electric duct heaters are commonly available with features such as cooling options, integrated/adjustable thermostats and thermowells.

Duct Heaters Image Provided by Watlow Electric Manufacturing Company