Installation Guide
29
3/8" 1/2" 5/8" 3/4" 7/8" 1/2" 3/4" 1" 1-1/4" 1-1/2"
10 39 92 199 329 501 275 567 1,071 2,205 3,307
20 26 62 131 216 346 189 393 732 1,496 2,299
30 21 50 107 181 277 152 315 590 1,212 1,858
40 19 41 90 145 233 129 267 504 1,039 1,559
50 18 37 79 131 198 114 237 448 913 1,417
60 16 35 72 121 187 103 217 409 834 1,275
80 13 29 62 104 155 89 185 346 724 1,066
100 11 26 55 9 0 138 78 162 307 630 976
125 10 24 48 8 1 122 69 146 275 567 866
150 9 21 43 7 2 109 63 132 252 511 787
200 8 19 39 6 6 100 54 112 209 439 665
250 8 17 36 60 93 48 100 185 390 590
Tubing Size, O.D. Type L
Nominal Pipe Size
Schedule 40
Pipe or
Tubin g
Length
Feet
*Data in accordance with NFPA pamphlet No. 54
Propane Gas Piping Chart II
C
IRCULATING
A
IR
& F
ILTERS
DUCT WORK - AIR FLOW
N
EVER
ALLOW
THE
PRODUCTS
OF
COMBUSTION
,
INCLUDING
CARBON
MONOXIDE
,
TO
ENTER
THE
RETURN
DUCT
WORK
OR
CIRCULATION
AIR
SUPPLY
.
WARNING
Duct systems and register sizes must be properly designed for
the CFM and external static pressure rating of the furnace. De-
sign the ductwork in accordance with the recommended meth-
ods of “Air Conditioning Contractors of America” Manual D.
Install the duct system in accordance with Standards of the Na-
tional Board of Fire Underwriters for the Installation of Air Con-
ditioning, Warm Air Heating and Ventilating Systems. Pamphlets
No. 90A and 90B.
A closed return duct system must be used, with the return duct
connected to the furnace. NOTE: Ductwork must never be at-
tached to the back of the furnace. For upflow installations re-
quiring 1800 CFM or more, use either two side returns or bottom
return or a combination of side /bottom. Flexible joints may be
used for supply and return connections to reduce noise transmis-
sion. To prevent the blower from interfering with combustion air
or draft when a central return is used, a connecting duct must be
installed between the unit and the utility room wall. Never use a
room, closet, or alcove as a return air chamber.
CHECKING DUCT STATIC
Refer to your furnace rating plate for the maximum ESP (ex-
ternal duct static) rating.
Total external static refers to everything external to the fur-
nace cabinet. Cooling coils, filters, ducts, grilles, registers
must all be considered when reading your total external static
pressure. The supply duct pressure must be read between
the furnace and the cooling coil. This reading is usually taken
by removing the “A” shaped block off plate from the end on
the coil; drilling a test hole in it and reinstalling the block off
plate. Take a duct static reading at the test hole. Tape up
the test hole after your test is complete. The negative pres-
sure must be read between the filter and the furnace blower.
Too much external static pressure will result in insufficient
air that can cause excessive temperature rise. This can cause
limit switch tripping and heat exchanger failure.
To determine total external duct static pressure, proceed as
follows;
1. With clean filters in the furnace, use a draft gauge (in-
clined manometer) to measure the static pressure of the
return duct at the inlet of the furnace. (Negative Pres-
sure)
2. Measure the static pressure of the supply duct. (Positive
Pressure)
3. The difference between the two numbers is .4” w.c.
Example:
static reading from return duct = -.1" w.c.
static reading from supply duct = .3" w.c.
total external static pressure on this system = .4" w.c.
NOTE: Both readings may be taken simultaneously and read
directly on the manometer if so desired. If an air conditioner
coil or Electronic Air Cleaner is used in conjunction with the
furnace, the readings must also include theses components,
as shown in the following drawing.
4. Consult proper tables for the quantity of air.
If the total external static pressure exceeds the maximum
listed on the furnace rating plate, check for closed dampers,
registers, undersized and/or oversized poorly laid out duct
work.
The temperature rise of the furnace must be within the tem-
perature rise range listed on the furnace rating plate.
Checking Static Pressure
(80% Furnace Shown, 90% Similar)
Figure 39