23 terms

to produce heat and deliver it ot a specific area

what is the job of an electric furnace?

using the temperature rise method

what is the easiest way to determine what the air flow of an electric furnace actually is?

subtract the temperature of the air entering the furnace from the temperature of the air leaving the furnace

how is the furnace TD calculated?

the therometer would pick up radiant heat produced by the elements and would cause a higher reading

why should you not place the thermometer where it can "see" the coils of the element?

at the furnace disconnect

where can the voltage and amp draw of the furnace be obtained?

fan motor adds heat to the circulated air

why should you be sure to measure the total current- including the fan motor amperage?

measure each set and add to get the total amperage

what should be done if the furnace has more than one set of power lines?

(volts X amps X 3.41) divided by (1.08 X temp rise)

what is the formula for calculating the furnace CMF?

furnace data plate

where can the minimum allowable CMF for a particular model furnace be found?

(230 X 30 X 3.41) / (1.08 X 28) = 778

what is the CMF of an electric furnace that draws 30 amps, at 230 volts, and the temperature rise is 28 degrees?

the return air section

what is one of the most often neglected parts of the heating systems?

the total free area of the grills and registors could be too small

how could registers and return air grilles prevent sufficient air movement through the system?

turn off the electrical power

before removing any of the furnace panels, what should the owner be cautioned to do?

thermostat operation, location and operation of the electrical disconnect and power suppley fuses, and filter maintenance

wht three items should be explained to the customer before leaving an installation?

more air is needed to keep the heating elements form overheating (if elements start to glow red, they will burn out)

why is the discharge air temp not as hot with an electric furnace ans it is with a gas or oil furnace?

3.41

what is the number of btus per watt?

62.4 X 240 X 3.41 = 51113

what is the btu output of an electric furnace whose amp draw is 62.4 amps at 240 volts for all three elements?

find amp draw of one element (240 / 23 = 10.43 amps) then (3 X 10.43 = 31.29 amp draw of 3 elements) then ( 31.29 X 240 X 3.41 = 25608)

what is the btu output for the elements of an electric furnace which is using 3 elements rated at 240 volts with resistance of 23 ohms per element?

volts X amps X square root of 3 X 3.41

what is the formula for finding the btu output for 3 phase electric heating elements?

480 X 23 X 1.72 X 3.41 = 64751

what is the btu output of a 3 phase electric furnace with each leg drawing 23 amps while supplied with 480 volts?

12000

how many btus equal 1 ton?

400

how many cmf equal 1 ton?

500

how many square feet equal 1 ton?