Valley Comfort Systems Inc
1290 Commercial Way, Penticton, B.C. V2A 3H5 250-493-7444
Version 1.04 13 Date printed: February 15, 2008
Typical installation illustration
PRESSURE LOSS
Before any changes are made to the existing furnace system you must establish the working pa-
rameters of that system. You can then insure that addition of the add-on has not degraded the
operation of the original system, and correct air flow will be maintained. Change all filters in the
system to insure maximum free air flow. Using an accurate manometer check the static pressure
at the end of a typical duct near the exit to the house. Check the static pressure in the plenum
above the existing furnace also.
Pressure drop = Static pressure at furnace -(minus) static pressure at duct exit
Record the pressure drop of the original system.
Addition of the add-on furnace will add airflow resistance in the system. After installation is com-
plete measure the pressure drop in the same run measured before add-on installation. If the air
flow has diminished the blower speed should be adjusted to compensate. When using a belted
blower the pulley size should be changed or adjusted to speed up the blower. If the pulley size is
adjusted measure the blower motor current to insure that it is still within the nameplate rating. It
may be necessary to replace the motor with a more powerful motor. If a direct drive blower is
used change to a higher speed. Do not change the blower size.
