Page 10
 WARNING
Improper installation of the furnace can result in 
personal injury or death. Combustion and ue products 
must never be allowed to enter the return air system 
or air in the living space. Use sheet metal screws and 
joint tape to seal return air system to furnace. In platform 
installations with furnace return, the furnace should be 
sealed airtight to the return air plenum. A door must 
never be used as a portion of the return air duct system. 
The base must provide a stable support and an airtight 
seal to the furnace. Allow absolutely no sagging, cracks, 
gaps, etc.
For no reason should return and supply air duct systems 
ever be connected to or from other heating devices 
such as a replace or stove, etc. Fire, explosion, carbon 
monoxide poisoning, personal injury and/or property 
damage could result.
Top
Bottom (Floor)
Left Side Right Side
Top/Plenum 1 in. (25 mm)
*Front 0
Back 0
Sides 0†
Vent 0
Floor 0‡
*Front clearance in alcove installation must be 24 in. (610 mm).
Maintain a minimum of 24 in. (610 mm) for front service access.
†Allow proper clearances to accommodate condensate trap.
‡For installations on a combustible floor, do not install the furnace
directly on carpeting,  tile  or  other combustible materials other
than wood flooring.
FIGURE 12 
Return Air Guidelines
Return air can be brought in through the bottom or either 
side of the furnace installed in an upow application. If the 
furnace is installed on a platform with bottom return, make 
an airtight seal between the bottom of the furnace and the 
platform to ensure that the furnace operates properly and 
safely. The furnace is equipped with a removable bottom 
panel to facilitate installation.
Markings are provided on both sides of the furnace cab-
inet for installations that require side return air. Cut the 
furnace cabinet at the maximum dimensions shown on 
page 2.
Refer to Engineering Handbook for additional information.
ML296UHV applications which include side return air and 
a condensate trap installed on the same side of the cab-
inet (trap can be installed remotely within 5 ft.) require 
either a return air base or eld-fabricated transition to ac-
commodate an optional IAQ accessory taller than 14.5”. 
See gure 13.
Side Return Air
(with transition and filter)
Return
Air
Plenum
Transition
20” X 25” X 1”
(508mmX635mmX 25mm)
Air Filter
FIGURE 13