Aluminum Pipe & Special Fittings

FLEX-DUCT CONNECTOR

FRESH AIR INTAKE VENTS Vents with molded 1/4” plastic screen

CAT. NO. DESCRIPTION 2R399

EACH Wide mouth hood with pipe, White - 3”

4G9451 Wide Mouth Hood, White - 4” 4G8890 Replacement Vent Hood, White - 4”

$6.37 $5.49

Strong fireproof 3” wide fabric strip fastened on each side to a gal- vanized metal strip 1-3/4” wide. Provides a convenient leak proof connection between furnace and plenum or plenum and trunk.

FRESH AIR INTAKE VENT Vent with fixed louver face.

CAT. NO. DESCRIPTION 4G9452

Fixed louver hood, White - 6”

EACH $9.68

Shipped in 100 foot coils. Roll into round duct or rake into square duct as required.

CAT. NO. MFG. NO. 8H952

8H952C DESCRIPTION

CN RG100 Flexible Duct Connector CN G100

Commercial Flexible Duct Connector EACH

$197.73 $371.33

HOW MANY CFM IS THE SYSTEM PRODUCING?

We all know how many CFM is required for a particular installation, or what the heat rise across the heat exchanger should be. But, do we know what CFM is being produced by the system? Maybe not.

We can determine the CFM through a simple calculation. CFM = Heating output 1.08 x temp Rise

The temperature rise is the difference between the return air temperature and the supply air temperature, measured at the equipment.

Example: A 50, 000 BTU, 80% gas furnace. The actual OUTPUT = 0.80 x 50,000 Or 40,000 BTU’s output. Let’s say the return air temp is 70 degrees F, and the discharge temp is 115 degrees F. The temperature difference is 45 degrees F.

Apply these numbers to the formula: CFM = 40,000 1.08 x 45 or

40,000 = 823 CFM 48.6

Why is this important if we already know the furnace is operating within the recommended temperature rise across the heat exchanger? We can use this information as a service tool. We can calculate the CFM on high speed blower simply by applying this tool. If we were running the above furnace on high speed and had a 2-1/2 ton split system air conditioning coil and unit connected to it, we could immediately determine that we have insufficient airflow to support the air conditioning equipment. Remember, coil freeze ups can be attributed to a number of causes, one of which is airflow. Being able to calculate the system airflow is a valuable tool providing us with information to analyze system performance, or lack of it. Above we determined how to calculate the CFM on a furnace installation. How would we calculate the CFM on an air handler? First, we need to determine if the air handler has electric heat installed and if it is functioning properly. We can check the voltage and amperage on the electric heat and compare it to the rating plate, or KW of the heater.

IE: 10 KW heater = 10,000 watts (Watts = volts x amps) 10,000 watts = 230 volts x? OR 10,000 watts = 43.5 amps. 230 volts

If the measured amperage is approx 43– 44 amps, we know the electric heater is functioning. Remember the formula to determine CFM? CFM = Heating out put 1.08 X temp rise

How do we calculate the “heating output” on the air handler? Easy! We already know that one watt equals 3.414 BTU’s, and we already know that watts are a measurement of volts times amps. If we know the KW of the heater, we simply multiply the watts by 3.414 to get the BTU’s. If we cannot read the KW’ on the heater plate, we can determine the wattage by multiplying the volts by the amps. Using the measurements we took previously, 230V x 43.5 amps = 10,005 watts (10 KW) and 10,005 watts x 3.414 = 34,141 BTU’s output. Let’s say the measured temp rise was 40 degrees F. Now simply apply the result to the original formula: CFM = 34,141 BTU’s = 790 CFM 1.08 x 40 F

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