A furnace has 68°F return air and 125°F supply air. What is the temperature rise?
Answer in °F.
Show the answer
57 °F
Temperature rise = supply air temperature - return air temperature = 125°F - 68°F = 57°F.
Reference: Furnace temperature rise
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Heating practice questions
30 questions from the hvac fundamentals practice test.
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Heating practice test
10 questions, graded as you go, with the reason for every answer. No sign-up.
What this covers
- Temperature rise
- Efficiency
- Combustion
- Auxiliary heat
- Sequence of operation
- Safety controls
- Flame sensing
- Furnace types
- Venting
- Heat exchangers
- Heat pump operation
- Reversing valve
- Defrost
- Balance point
Sample questions
A gas furnace has an input of 80,000 Btu/h and runs at 80% efficiency. What is its heat output?
Answer in Btu/h.
Show the answer
64000 Btu/h
Output = input x efficiency = 80,000 Btu/h x 0.80 = 64,000 Btu/h.
Reference: Furnace input, output and efficiency
A furnace delivers 64,000 Btu/h to 1,200 CFM of air. Using Q = 1.08 x CFM x ΔT, what temperature rise should be measured? Answer to one decimal place.
Answer in °F.
Show the answer
49.4 °F
ΔT = Q / (1.08 x CFM) = 64,000 / (1.08 x 1,200) = 64,000 / 1,296 = 49.4°F.
Reference: Sensible heat formula applied to temperature rise