CP-1605
EQUIPMENT SELECTION AND SIZING
Proper sizing of system components is
crucial for proper operation.
Steps for sizing and selection:
1) Obtain room by room heat loss and/or
heat gain
2) Determine heating water temperature
3) Select air handler from specification
sheet
5) Determine duct layout
Heat Loss
Make sure a proper room-by-room heat
loss and heat gain for the dwelling is
calculated using HRAI, ASHRAE or other
approved sizing method.
Air Handler Selection
Select the desired air system that will
meet 100%-140% of the heating load
and 80%-120% of the cooling load.
If using a boiler system, select a boiler
that has an output that meets or exceeds
the heat loss of the space being heated.
If the boiler is meeting additional loads,
size the boiler to meet the total combined
load.
For combo heating systems, use an
approved sizing method such as the
Unified Combo Guidelines published by
HRAI. In areas where the UCG or a local
sizing code is not applicable, use the
following method for sizing combo
systems:
1) Select an air handler that meets or
exceeds the calculated heat loss at the
water heater operating temperature
(130F/55C or 140F/60C).
2) Select a water heater with an output
that is at least 120% of the heat loss
Duct Layout
Make sure a proper duct design has
been completed for the dwelling using
HRAI, ASHRAE or other approved
design method.
Supply air Plenum
Provide a supply air plenum that is the
same dimensions as the outlet flanges of
the air handler. A length of 36 inches is
recommended. Acoustic lining is
recommended.
A smooth, square-to-round transition
may be used in place of the supply air
plenum for horizontal installations where
there is only one supply main.
For vertical applications where the air
conditioning coil is installed in the supply
air plenum, the cooling coil must be
supported at least 4 inches (100mm)
above the heating coil face on brackets
or channel to ensure unimpeded airflow
through the heating coil.
Plenum takeoffs may be mounted on the
end of the plenum or the sides of the
plenum, but not both. Spin-in collars or
transition takeoffs may be used, but not
both.
Supply mains
Plan duct layout to avoid branch runs in
outside walls or attics and to minimize
the length of the main duct
