Manual

8. Turn on electricity at electrical disconnect switch
located next to furnace.
SECTION 25 — MEASURING DUCT WORK
STATIC PRESSURE.
Equipment Needed: Save time by getting these tools before
you start: Hern number(s) 20 listed in Section 10.
CAUTIONS High duct work static pressure may cause
low airflow resulting In poor heating performance and
reduced heat exchanger life. Low airflow may also cause
poor cooling performance.
A. Preparing to measure duct work static pressure.
1. Open supply air registers and return air grilles. Make
sure the registers and grilles are free of obstruction
from rugs, carpets, drapes or furniture.
2. Set balancing dampers in supply duct system.
3. Check duct work for obstructions or leaks.
4. Make sure fitters are clean and in place. See Section
17 for filter information,
5. Make sure that blower speed taps are set for proper
heating ar^d cooling. Рог heating operation, initial
speed tap should be set in accordance with Figure
37B. For cooling operation, initial speed tap should
be set in accordance with Figure 38. Refer to Sec
tion 24 for adjusting blower speed.
a.
Air Temperature Rise Range
and Heating Operation Speed Taps
-BTU/HR/Motor
Input/ HP
Air Temperature
Rise Range (*’F)
Heating Operation
‘Speed Tap
40,000 / 1/4 50-80
LO
40,000 / 1/3
30-60 LO
60,000 / 1/4
45-75 ML
60,000 / 1/3
45-75 LO
60,000 / 1/2
35-65 LO
80.000 / 1/4
50-80 MH
80,000 / 1/3
40-70 MH
80,000 / 1/2
50-80 LO
80,000 / 3/4
40-70 LO
100.000 / 1/3
55-85 MH
100,000 / 1/2 50-80
ML
100,000 / 3/4
40-70 ML
120,000 / 1/2
45-75
MH
120,000 / 3/4
45-75
MH
140,000 / 3/4
45-75
MH
140,000 / 3/4
50-80
MH
” These are initial Factory Settings.
— See Furnace Rating Plate for BTU/HR input and
Motor H.P.
FIGURE 37B
Heating.
1.
2.
Measure duct work static pressure with cir
culating air blower on heating speed. Fol
low instructions below.
Measure air temperature rise with circulat
ing air blower on heating speed. See Sec
tion 26.
b.
Air Conditioning.
1. Measure duct work static pressure with cir
culating air blower on air conditioning
speed. Follow instructions below.
2. Measure air temperature rise with circulat
ing air blower on heating speed. See Sec
tion 26.
Air Conditioning Operation Speed Tap Settings
with 0.5" W.C. Ductwork Static Pressure
Air
input /
HP
1—1/2 2 2—1/2
3 3—1/2 4
s
40,000
/ 1/4 MH HI — —
—
—
40,000
/ 1/3
—
ML
MH HI
—
—
—
60,000 / 1/4 MH HI
— — — — —
60,000 / 1/3
—
ML
MH HI
—
60,000 / 1/2 —
—
—
ML MH HI
—
60,000
/ 1/4 H) HI
— — — —
80,000 / 1/3 LO ML
HI
HI
— — —
80,000 / 1/2
—
— —
ML MH HI
80,000
/ 3/4
—
— —
— ML
MH HI
100,000 / 1/3 LO ML HI HI
— —
—
100,000 / 1/2 — LO
MH
MH HI — —
100,000 / 3/4
— — —
LO
MH MH HI
120,000 / 1/2
— —
LO
ML HI
HI —
120,000 / 3/4
—
—
—
LO ML
HI HI
140,000
/ 3/4
—
—
LO
ML HI
HI
—
140,000 / 3/4
— — —
LO
ML HI HI
See furnace rating plate for BTU/HR input and motor
H.P.
This table only gives initial speed tap settings for
installations with ductwork static pressure of 0.5”
W.C. figuring 400 CFM per ton of air conditioning.
Ductwork with higher than 0.5" W.C. static pressure
will cause reduced airflow and these speed tap set
tings will not be correct. To determine correct speed
tap settings at ductwork static pressures above 0.5”
W.C., see Product Data Sheet.
FIGURE 38
B. Measuring duct work static pressure.
1. Place slope gauge near furnace where level and
adjust scale to read 0.00 inches W.C.
2. Insert one static pressure tap into supply air transi
tion duct between furnace and cooling coil or in the
supply air plenum for heating only systems. Insert
other static pressure tap in return air plenum. See
Figure 39.
31