All grilles are undersized from the nominal-duct dimensions
in order to fit ductwork, and the linear units are no exception. The stack head
is the part of the grille that is installed into the wall opening and
associated ductwork or plenum. We start our sizing from the inside of the stack
head because this is the business part of the unit through which the air passes
and performance data is consistent regardless of the border width.
The inside of the linear bar grille stack head is undersized
from the nominal, or duct dimension by ¾”. The floor frames, type 5 and 6, are
the exception at 3/8". The undersized dimension represented in our marketing
literature is D-¾”, or “Duct” minus ¾”. If a dimension is specified as 12, the
inside of the stack head will be 11-¼”; This applies to the length and width of
a unit. The outside or overall dimension is 11-¼” plus two border widths (Plus
two mounting-frame widths for the combination frames that use both a border and
frame).
Cut dimensions for mounting the units can vary from the loose
fit of the specified D dimension to a tight fit of D-5/8”. The tighter fit is
beneficial to the screw-mounting option as it provides the most overlap or “meat”
into which the screw is installed, particularly for sheet-rock surfaces. The
loose fit of a D cutout is flexible and should be used for combination frame
& borders, spring-clip mounting, concealed-mounting, or to provide
clearance for a plenum boot -- by others -- to be installed. Titus does not provide
plenum boots for linear bar diffusers.
Floor frames (Type 5, 6 & 15) and combination frames that
utilize a mounting frame (Types 1 through 4) are a little different in that the
outside of the stack head or mounting frame correlates exactly to D. For these
units, the cutout should be slightly oversized at D+1/8” to provide clearance
for the weld beads at the corners of the frames.
There are two particular notes I would like to make involving
narrow frame styles 7, 11 and 12. First, the type 11 and 12 frames offer a
screw-mounting option (A). When the A option is used, it is important to
consider upsizing the grille or making sure that the tight cutout used will provide
a secure base for screw-mounting. If the D dimension is used, the screw holes
provided in the frames may coincide with the opening; Installation becomes much
more complicated. Concealed mounting is the preferable mounting option for
these frames.
The type-7 frame does not offer the screw-mounting option, so
a concealed fastening must be used. This frame style was originally designed
for the type-4 combination frame, but the narrow border width makes it
attractive to those desiring the least amount of exposed grille for aesthetic
purposes. You will note that because of its primary use as the core of a
combination frame, the D dimension actually falls outside the overall (O)
dimension. Therefore, a unit size of 12" x 12” should not be installed in a 12" x
12” cutout. The tight fit cutout of D-1/2” should be used, or the unit needs to
be oversized by 1/2” if the D cutout will be used.
Please direct questions toward Titus Communications (communications@titus-hvac.com) and/or Titus' GRD Product Manager Mark Costello (mcostello@titus-hvac.com).
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