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2.4 General Installation
1. It is the customer and installation personnel responsibility to determine if the duct
furnace is equipped with all of the safety devices required for the particular application.
Safety considerations include the accessibility of the equipment to non-service
personnel, the provision of electrical lockout switches, maintenance procedures, and
automatic control sequences.
2. Duct furnaces must be level. Failure to provide a level-mounting surface for the duct
furnace will result in a variety of operational problems.
3. Clearly identify all emergency shut off devices.
4. Make duct connections to the casing by applying caulking around the connection and
screwing flanged ducts directly to the casing and/or flange with self-tapping sheet metal
screws. It is important to seal all duct connections to prevent air leakage and system
performance problems. Ducts connected to the furnace shall have removable access
panels on both the upstream and downstream sides of the furnace. These openings
shall be accessible when the furnace is installed and shall be sized to allow the
observation of smoke or reflected light inside the casing to indicate the presence of
leaks in the heat exchanger. The covers for the openings shall be attached in such a
manner as to prevent leaks.
5. The furnace must not be operated in the presence of chlorinated vapors. When such
vapors mix with the products of combustion, highly corrosive compounds result, which
will cause the premature failure of the heat exchanger and other components.
6. If installing a duct furnace model, IFD, the furnace is connected to a return air duct or
any other inlet air restriction, the duct furnace shall be installed on the positive pressure
side of the air-circulating blower.
7. When the duct furnace is installed in an enclosed duct furnace room it is imperative that
the duct furnace room itself is not used as an air plenum. Ductwork must be used for all
supply and return air to and from the duct furnace, as well as any other fans, which may
be installed in the same room.
2.5 Drains and Traps
1. Heat Exchanger Condensate - These duct furnaces are supplied with a condensation
removal pipe connection. Condensate from the heat exchanger is acidic and may
contain chemical compounds requiring special drainage. The drain must be installed in
accordance with all plumbing codes. The condensate is to be drained via 1/2" PVC or
steel pipe with an indirect connection to the plumbing wastes. Where a condensate
neutralizer is used, an overflow shall be provided such that condensate will be directed
to the drain in the event that the neutralizer becomes plugged. Indoor installations
typically require a condensate trap to be installed to prevent combustion gases entering
the space. Outdoor duct furnaces may require special attention to drains to prevent
freezing and clogging of the drain line.
2. Since the condensate is drained by gravity, avoid long runs of drain piping. If a long run
of trapping cannot be avoided or the piping has water flow restrictions such as several
elbows, add extra height to provide enough hydrostatic head to overcome the frictional
losses. Always slope piping down a minimum of 1/8" per foot in the direction of the flow.
