A homeowner wants to calculate the heat loss through a wall section that is 10 feet wide by 8 feet high with R-20 insulation. If the temperature difference is 40°F, what is the heat loss in BTU/hour?
Correct Answer
C) 160 BTU/hour
Heat loss = (Area × Temperature difference) ÷ R-value = (80 sq ft × 40°F) ÷ 20 = 160 BTU/hour.
Why This Is the Correct Answer
The heat loss formula is: Q = (Area × ΔT) ÷ R-value. Area = 10 ft × 8 ft = 80 sq ft. ΔT = 40°F. R-value = 20. Q = (80 × 40) ÷ 20 = 3,200 ÷ 20 = 160 BTU/hour. This formula quantifies the rate of heat transfer through a building assembly based on its insulating resistance.
Why the Other Options Are Wrong
Option A: 120 BTU/hour
120 BTU/hour does not result from correct application of the heat loss formula. It may arise from an arithmetic error such as using an incorrect area (e.g., 60 sq ft instead of 80) or applying the formula incorrectly.
Option B: 320 BTU/hour
320 BTU/hour is double the correct answer. This error typically results from multiplying by R-value instead of dividing: 80 × 40 ÷ 10 = 320, or perhaps using R-10 instead of R-20. Candidates who confuse the direction of R-value's effect (higher R = less heat loss) may arrive here.
Option D: 200 BTU/hour
200 BTU/hour would result from using an incorrect area, such as only using one dimension (10 × 40 ÷ 20 = 20, scaled up) or a mathematical error in dividing 3,200 by 16 instead of 20. The formula setup is correct but the arithmetic is off.
Memory Technique
Q = A × ΔT / R. Remember: R is in the denominator because more resistance = less heat loss. Think 'R Resists heat, so it goes on the bottom.' Area (80 sq ft) × Delta-T (40°F) = 3,200 ÷ R-20 = 160 BTU/hr.
More Michigan Questions
A residential foundation wall in Michigan is 8 feet high with 2 feet above grade. The backfill exerts lateral pressure of 30 psf per foot of depth. What is the maximum lateral pressure at the bottom of the foundation wall?
A builder discovers that the electrical service entrance was installed without proper permits. According to Michigan law, what is the most appropriate next step?
What is the maximum allowable span for a 2x8 floor joist (Grade 2 Douglas Fir) at 16" O.C. with 40 psf live load and 10 psf dead load according to Michigan Building Code span tables?
According to Michigan Building Code, what is the maximum height of a wood-framed bearing wall using 2x4 studs with standard construction?
A homeowner requests to convert a bedroom into a bathroom on the second floor. What is the primary Michigan code concern the builder must address?
According to Michigan plumbing regulations, what is the minimum pipe size required for a water service line serving a single-family residence?
A contractor is building a basement foundation wall that is 8 feet high and will retain 6 feet of soil. What is the minimum wall thickness required by the Michigan Building Code for poured concrete?
A homeowner wants to install a gas fireplace in their living room. The contractor notices the existing gas line is 1/2 inch black iron pipe. For a 40,000 BTU fireplace with a 25-foot run, is this pipe size adequate according to Michigan gas code?
During a framing inspection, the building official notes that the contractor used 2x4 studs at 24 inches on center for an exterior wall. According to Michigan Building Code, what is the maximum wall height allowed for this configuration?
A contractor is installing a beam to support floor joists. The beam must carry a total load of 8,000 pounds over a 12-foot span. If the allowable fiber stress for the lumber grade is 1,200 psi, what is the minimum required section modulus?
People Also Study
Business & Financial Management
120 questions · 70% to pass
Contract Administration
60 questions · 70% to pass
Project Management
60 questions · 70% to pass