HERS HVAC System Evaluation 3 — Questions and Answers
Question 1: A rater measures duct leakage to outside (Qn,out) at 6% of conditioned floor area on a new construction home. Does this meet the 2021 IECC requirement?
- Yes, 6% is within the 8% allowance
- No, 2021 IECC requires ≤4 CFM25 per 100 sq ft to outside (Correct answer)
- Yes, the standard only applies to total leakage not leakage to outside
- No, 2021 IECC requires zero duct leakage to outside
Correct answer: No, 2021 IECC requires ≤4 CFM25 per 100 sq ft to outside
The 2021 IECC requires duct leakage to outside not to exceed 4 CFM25 per 100 square feet of conditioned floor area.
Question 2: What is the purpose of measuring static pressure across the air handler in HVAC system evaluation?
- To determine the refrigerant charge level
- To verify that the system is operating within the manufacturer's specified external static pressure range (Correct answer)
- To measure the latent cooling capacity
- To calculate duct leakage in CFM25
Correct answer: To verify that the system is operating within the manufacturer's specified external static pressure range
Measuring external static pressure confirms the system operates within manufacturer specifications; excessive static pressure reduces airflow, efficiency, and equipment life.
Question 3: Which ventilation standard is referenced in RESNET guidelines to determine whole-house mechanical ventilation requirements for HERS ratings?
- ASHRAE 90.1
- ASHRAE 62.2 (Correct answer)
- ACCA Manual Q
- EPA Indoor Air Quality Guide
Correct answer: ASHRAE 62.2
ASHRAE 62.2 'Ventilation and Acceptable Indoor Air Quality in Residential Buildings' is the referenced standard for whole-house mechanical ventilation in HERS ratings.
Question 4: A home uses a ground-source heat pump (GSHP). Which efficiency metric is most relevant for evaluating its heating performance?
- AFUE
- COP or EER at ARI/AHRI rating conditions (Correct answer)
- HSPF
- SEER2
Correct answer: COP or EER at ARI/AHRI rating conditions
Ground-source heat pumps are rated by COP (Coefficient of Performance) at standardized ARI/AHRI ground-loop conditions rather than HSPF, which applies to air-source units.
Question 5: When a HERS rater finds that a gas furnace has a cracked heat exchanger, what is the primary concern?
- Reduced heating capacity causing Manual J violations
- Carbon monoxide may enter the air distribution system (Correct answer)
- The AFUE rating will drop below minimum standards
- Increased duct leakage due to pressure imbalance
Correct answer: Carbon monoxide may enter the air distribution system
A cracked heat exchanger allows combustion gases including carbon monoxide to mix with supply air, creating a serious health and safety hazard.
Question 6: In the context of HERS duct testing, what does 'Duct Leakage to Outside' (LTO) specifically measure?
- Total air loss from all duct connections
- Only duct leakage that exits the building thermal envelope into unconditioned or outdoor spaces (Correct answer)
- Return air leakage from outside the building
- Intentional outdoor air intake for ventilation
Correct answer: Only duct leakage that exits the building thermal envelope into unconditioned or outdoor spaces
Duct Leakage to Outside measures only the portion of duct leakage that crosses the building's thermal envelope into unconditioned attics, crawlspaces, garages, or outdoors.
Question 7: A rater is verifying airflow for a 3-ton cooling system. According to ACCA standards, what is the target airflow rate per ton of cooling capacity?
- 200 CFM per ton
- 300 CFM per ton
- 400 CFM per ton (Correct answer)
- 500 CFM per ton
Correct answer: 400 CFM per ton
ACCA and most manufacturers specify approximately 400 CFM per ton of cooling capacity as the design target for proper latent and sensible heat removal.
HERS HVAC System Evaluation 3
A rater measures duct leakage to outside (Qn,out) at 6% of conditioned floor area on a new construction home.
Does this meet the 2021 IECC requirement?