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EMS HVAC contractor licensing practice test

Q. A 75,000 btuh furnace (80% AFUE) has a temperature rise of 45F. What is the furnace CFM?

The below questions are similar to those asked when attempting to get your HVAC contractors, Masters or journeyman license. This practice test is not intended for those seeking  a certification in service, such as NATE. The test is for those seeking an HVAC contractor or master license. Our practice test is absolutely FREE. You may take the test as many times as you wish. If you wish to save time, the answers, and where we got them, are available HERE for a measely 40 bucks.

Answer:

                                     One of the basic equations used in hvac design is BTU = CFM x 1.1 X TD (TD may be substituded with TR). The equation may be changed around as: 

CFM = BTU / (1.1 X TD) 

or   TD= BTU / (1.1 X CFM).  

The above question is asking for CFM, therefore, we will use the equation CFM = BTU / (1.1 x TR).  

  BTU = 75,000 x .80 ( because the furnace is 80% efficient, we must use the output rating, which is 60.000 BTUH, AFUE X input rating)

CFM = BTU / (1.1 X TR)

CFM = 60,000 BTUH/ (1.1 X 45) 

CFM = 60000 BTUH / 49.5 = 1212 CFM

           Another example, using the above equation is “What is the heat loss of a structure being ventilated with 300 cfm of out door air at 20F?

70F indoor temp minus 20F outdoor tem = 50F TD

BTU = CFM x 1.1 X TD         300CFM x 1.1 x 50 =  16,500 BTUH

                                  

If you want to learn a whole lot more, check out our HVAC prep course at hvaclicensing.com

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