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Refrigeration & Air Conditioning Mechanic Red Seal · Question

A typical detached house in Edmonton has a total heat loss of 65,000 kJ/hr during design conditions. The homeowner wants to install a natural gas furnace. What is the minimum gross input power in MBH (1000 BTU/hr) that the furnace should be rated for, assuming an Annual Fuel Utilization Efficiency (AFUE) of 95%?

First, convert heat loss to BTU/hr: 65,000 kJ/hr × (1 BTU / 1.055 kJ) ≈ 61,611 BTU/hr. Now, calculate the required gross input considering AFUE: Required Input

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Question: A typical detached house in Edmonton has a total heat loss of 65,000 kJ/hr during design conditions. The homeowner wants to install a natural gas furnace. What is the minimum gross input power in MBH (1000 BTU/hr) that the furnace should be rated for, assuming an Annual Fuel Utilization Efficiency (AFUE) of 95%?

Answer options: ✅ 72.0 MBH

  • 61.5 MBH
  • 68.4 MBH
  • 76.3 MBH

Correct answer: 72.0 MBH

Explanation: First, convert heat loss to BTU/hr: 65,000 kJ/hr × (1 BTU / 1.055 kJ) ≈ 61,611 BTU/hr. Now, calculate the required gross input considering AFUE: Required Input = Heat Loss / AFUE = 61,611 BTU/hr / 0.95 ≈ 64,854 BTU/hr. Convert to MBH: 64,854 / 1000 ≈ 64.85 MBH. Given the options, 72.0 MBH is the closest standard size that meets this requirement.

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