Installation manual

ManualsBrandsUnitary products group ManualsDomestic AppliancesG9T-DH

035-19599-001 Rev. A (1103)

26 Unitary Products Group

APPLYING FILTER PRESSURE DROP TO

DETERMINE SYSTEM AIRFLOW

To determine the approximate airflow of the unit with a filter in place, fol-

low the steps below:

1. Select the filter type.

2. Select the number of return air openings or calculate the return

opening size in square inches to determine the proper filter pres-

sure drop.

3. Determine the External System Static Pressure (ESP) without the

filter.

4. Select a filter pressure drop from the table based upon the number

of return air openings or return air opening size and add to the

ESP from Step 3 to determine the total system static.

5. If total system static matches a ESP value in the airflow table (i.e.

0.20 w.c. (50 Pa), 0.60 w.c. (150 Pa), etc,) the system airflow cor-

responds to the intersection of the ESP column and Model/Blower

Speed row.

6. If the total system static falls between ESP values in the table (i.e.

0.58 w.c. (144 Pa), 0.75 w.c. (187 Pa), etc.), the static pressure

may be rounded to the nearest value in the table determining the

airflow using Step 5 or calculate the airflow by using the following

example.

Example: For a 130,000 BTUH (38.06 kW) furnace with 2 return open-

ings and operating on high-speed blower, it is found that total system

static is 0.58” w.c. To determine the system airflow, complete the follow-

ing steps:

Obtain the airflow values at 0.50 w.c. (125 Pa) & 0.60 w.c. (150 Pa)

ESP.

Airflow @ 0.50”: 2125 CFM (60.17 m

/min)

Airflow @ 0.60”: 2035 CFM (57.62 m

/min)

Subtract the airflow @ 0.50 w.c. (125 Pa) from the airflow @ 0.60 w.c.

(150 Pa) to obtain airflow difference.

2035 - 2125 = -90 CFM (2.55 m

/min)

Subtract the total system static from 0.50 w.c. (125 Pa) and divide this

difference by the difference in ESP values in the table, 0.60 w.c.

(150 Pa) - 0.50 w.c. (125 Pa), to obtain a percentage.

(0.58 - 0.50) / (0.60 - 0.50) = 0.8

Multiply percentage by airflow difference to obtain airflow reduction.

(0.8) X (-90) = -72

Subtract airflow reduction value to airflow @ 0.50 w.c. (125 Pa) to

obtain actual airflow @ 0.58 inwc (144 Pa) ESP.

2125 - 72 = 2053

Field Installed Accessories - Non-Electrical

Model No. Description Use With

1NP0347

Propane (LP) Conversion

Kit all Models Except 140 MBH

1NP0349 LP Conversion Kit for 140 MBH Models

1CT0302 Concentric Intake/Vent 2” Pipe

1CT0303 Concentric Intake/Vent 3” Pipe

1PS0306