Chapter 23 Quiz
Multiple Choice
1. AFUE stands for Annual Fuel Utilization Efficiency. An AFUE of 80% means:
a) The furnace operates at full capacity 80% of the time b) 80% of the fuel's heat content is converted to useful heat delivered to the home; 20% is lost as exhaust c) The furnace meets 80% of the home's heating load; supplemental heat covers the rest d) 80% of electrical energy is converted to heat; 20% is lost to resistance
Answer: b — AFUE directly measures what fraction of fuel energy becomes useful heat. The remaining 20% exits through the flue as hot exhaust gases.
2. The 2023 transition from SEER to SEER2 resulted in:
a) Higher numerical ratings for the same equipment, due to more favorable test conditions b) Lower numerical ratings for the same equipment, due to a more rigorous test procedure c) No change in ratings — SEER2 is simply a rebranded name for the same standard d) SEER2 replaced only heating efficiency ratings; cooling still uses original SEER
Answer: b — The M1 test standard used for SEER2 applies higher external static pressure, representing real-world conditions more accurately. The result is numerically lower ratings for the same equipment — approximately 5% lower than old SEER ratings.
3. A heat pump with a COP of 3.0 means:
a) The heat pump uses 3.0 times more electricity than a standard furnace b) For every unit of electricity consumed, the heat pump delivers 3 units of heat energy c) The heat pump is 300% efficient, which is physically impossible d) The heat pump achieves its rated output only when outdoor temperature is above 30°F
Answer: b — COP of 3.0 is not only possible but common for heat pumps because they move heat rather than generate it. Moving heat from outdoor air to indoors is far more efficient than converting electricity to resistance heat (COP = 1.0 by definition).
4. The "Rule of 5000" is used to:
a) Determine when a furnace exceeds safe CO output levels b) Calculate the minimum BTU load for a given square footage c) Help decide whether to repair or replace aging HVAC equipment by multiplying repair cost by age d) Estimate the number of hours a new HVAC system should run annually
Answer: c — Rule of 5000: repair cost × system age in years. If the result exceeds 5,000, replacement is generally more cost-effective than repair.
5. Manual J is important to HVAC system replacement because:
a) It is required by federal law before any HVAC installation b) It calculates the home's actual heating and cooling load, which determines correct equipment size c) It documents the contractor's liability insurance requirements d) It provides the formula for calculating energy payback periods on high-efficiency equipment
Answer: b — Manual J is the ACCA standard for residential load calculation. Without it, contractors guess at equipment size — and typically oversize. Oversized equipment short-cycles, doesn't dehumidify well, and wears out faster.
6. A contractor quotes you a new furnace without mentioning a load calculation. This is a red flag because:
a) Contractors are required by law to perform load calculations before any installation b) Without a load calculation, the contractor is almost certainly oversizing the equipment, which reduces performance and longevity c) A quote without load calculation will always be higher in price d) Modern furnaces cannot be properly commissioned without load calculation data
Answer: b — Oversizing is the most common HVAC installation error. A contractor who skips the load calculation is defaulting to guesswork or an "always oversize for safety" approach that serves the equipment's short-cycle problems rather than the homeowner's comfort and efficiency.
7. In the gas vs. heat pump cost comparison, which of the following statements is most accurate?
a) Heat pumps always have lower operating costs than gas heating in any climate b) Gas heating always costs less than heat pump heating because fuel is cheaper than electricity c) The answer depends on local gas and electricity rates, system efficiency, and local climate — it's a calculation, not a general rule d) Heat pumps are only cost-competitive when gas prices exceed $2.00/therm
Answer: c — This question has no general answer. In markets with cheap gas and expensive electricity (Texas, Oklahoma), gas usually wins. In markets with expensive gas and relatively cheap electricity (Pacific Northwest, mid-Atlantic), heat pumps are often cheaper to operate. The calculation in Section 23.7 is the only reliable approach.
8. A dual-fuel heat pump system is best described as:
a) A system that can run on both propane and natural gas, switching based on price b) A heat pump paired with a gas furnace backup, where each runs when it's most efficient c) A split-system heat pump that provides both space heating and water heating d) A variable-refrigerant-flow system with two outdoor units for redundancy
Answer: b — A dual-fuel (hybrid) system runs the heat pump when temperatures are mild (heat pump is efficient) and automatically switches to the gas furnace when outdoor temperatures drop below the crossover point (heat pump efficiency drops below gas cost advantage). Best of both systems.
9. The Inflation Reduction Act Section 25C tax credit for heat pumps allows a credit of:
a) 10% of installed cost, up to $500 lifetime b) 30% of installed cost, up to $2,000 per year c) 50% of installed cost, up to $1,500 per year for households under $100,000 income d) Full cost of equipment (not labor), up to $3,000 per year
Answer: b — The IRA 25C credit is 30% of installed cost up to $2,000 for heat pumps, available annually through 2032. This is significantly more generous than the prior $500 lifetime credit.
10. HVAC maintenance contracts (service contracts) are most likely to provide good value when:
a) Your system is under 5 years old and covered by manufacturer warranty b) You own a heat pump in a very cold climate where efficiency drops rapidly c) You would not reliably schedule annual tune-ups without the contract structure, or when they include parts replacement d) You are planning to sell your home within two years
Answer: c — Service contracts make sense primarily when: (1) the contract structure ensures you actually do maintenance you'd otherwise skip, or (2) the contract includes parts replacement (capacitors, contactors) that can be expensive if needed. For homeowners who reliably schedule annual service, the value proposition is weaker.
Short Answer
11. Walk through the break-even calculation for replacing an 80% AFUE gas furnace with a 96% AFUE furnace in a household that uses 900 therms of gas per year for heating at $1.20/therm. What are the annual savings and simple payback if the high-efficiency furnace costs $1,000 more to purchase and install?
Model answer: Current cost: 900 therms × $1.20 = $1,080/year. Current useful heat: 900 × 80% = 720 therms equivalent of heat delivered. New system at 96% AFUE: to deliver same 720 therms of heat, requires 720 ÷ 0.96 = 750 therms of gas. New annual cost: 750 × $1.20 = $900/year. Annual savings: $1,080 - $900 = $180/year. Simple payback: $1,000 ÷ $180 = 5.6 years. This is a strong case for high-efficiency at end-of-life replacement. With available tax credits ($600 for high-efficiency gas furnace under Section 25C), payback shortens to (1,000 - 600) ÷ 180 = 2.2 years.
12. Why is the payback period for HVAC efficiency upgrades typically longer for cooling than for heating in most northern U.S. climates, and what factor makes cooling efficiency more important in southern markets?
Model answer: In northern climates, heating season is 5–7 months and the system runs many hours at high demand. Cooling season is shorter (2–4 months) and demand hours are fewer. The total annual BTUs of cooling work are relatively modest, so even a significant SEER2 improvement produces limited absolute dollar savings. In southern markets (Phoenix, Houston, Miami), cooling runs 7–10 months, often at high intensity, with 2,000–3,000+ annual full-load cooling hours compared to 800–1,200 in northern markets. The same SEER2 improvement that saves $80/year in Ohio might save $200/year in Texas. This is why the federal minimum efficiency standards for air conditioners are higher in southern and southwestern regions — the efficiency gain in those climates justifies stricter minimums.