HERS Energy Modeling & Analysis — Questions and Answers

Question 1: In REM/Rate or equivalent HERS software, what does the 'reference home' represent?

The highest-performing home in the neighborhood
A code-minimum home built to the same specifications as the rated home (Correct answer)
The national average energy consumption for similar homes
The rated home with all improvements applied

Correct answer: A code-minimum home built to the same specifications as the rated home

The reference home is a theoretical code-minimum version of the same home used as the baseline for calculating the HERS Index.

Question 2: Which parameter has the greatest impact on heating load calculations in cold climates when entering data into HERS software?

Window SHGC value
Wall assembly U-factor (Correct answer)
Water heater efficiency rating
Duct leakage to outside

Correct answer: Wall assembly U-factor

In cold climates, wall assembly U-factor directly drives conductive heat loss and dominates heating load calculations.

Question 3: When modeling a home with a sealed crawlspace in HERS software, how should the crawlspace be categorized?

Unconditioned space with vented floor assembly
Conditioned space with insulated walls (Correct answer)
Exterior exposure equivalent to a slab
Semi-conditioned with 50% heat loss factor

Correct answer: Conditioned space with insulated walls

A sealed crawlspace is modeled as conditioned space with insulation on the crawlspace walls rather than the floor above.

Question 4: A rater enters a furnace with AFUE of 0.96 into HERS software. What does the remaining 4% represent?

Energy lost to flue gases and jacket losses (Correct answer)
Energy used by the blower motor
Standby pilot light consumption
Duct distribution losses

Correct answer: Energy lost to flue gases and jacket losses

AFUE measures seasonal efficiency, and the 4% not converted to useful heat is lost through combustion exhaust and jacket radiation.

Question 5: Which of the following correctly describes how HERS software handles mechanical ventilation in the energy model?

Ventilation energy use is excluded from the HERS Index calculation
Ventilation fan watts and airflow are modeled as an energy load (Correct answer)
Only exhaust-only systems are recognized by the software
Ventilation is approximated using natural infiltration values only

Correct answer: Ventilation fan watts and airflow are modeled as an energy load

HERS software models mechanical ventilation by accounting for fan energy consumption and the conditioning load of outdoor air introduced.

Question 6: What is the purpose of entering an 'as-built' natural gas water heater's Energy Factor (EF) or Uniform Energy Factor (UEF) into HERS software?

To determine the correct pipe insulation R-value
To calculate annual domestic hot water energy consumption (Correct answer)
To set the water heater's recovery time in the model
To verify the unit meets combustion safety standards

Correct answer: To calculate annual domestic hot water energy consumption

EF/UEF is used by the model to estimate annual energy use for water heating based on efficiency, fuel type, and household demand.

Question 7: When modeling a home with photovoltaic (PV) panels in HERS software for a HERS Index calculation, what is the standard treatment of PV output?

PV output is ignored entirely in standard HERS ratings
PV generation offsets rated home energy use and can reduce the HERS Index below zero (Correct answer)
PV is entered only for the reference home calculation
PV output replaces the need to model mechanical systems

Correct answer: PV generation offsets rated home energy use and can reduce the HERS Index below zero

Under RESNET guidelines, on-site PV generation is credited against the home's energy use and can drive the HERS Index to zero or below (a 'zero energy' or 'energy positive' home).

Question 8: A HERS rater measures duct leakage to outside at 8% of system airflow. How should this value be entered into the energy model?

As total duct leakage including leakage to inside
As leakage to outside only, separate from total leakage (Correct answer)
As a duct efficiency multiplier between 0 and 1
As an equivalent leakage area in square inches

Correct answer: As leakage to outside only, separate from total leakage

HERS software distinguishes leakage to outside (which affects conditioned air loss) from total duct leakage, and each is entered separately.

Question 9: Which insulation metric is required when modeling attic insulation in HERS software?

Insulation material density in lb/ft³
Total R-value of the insulation assembly (Correct answer)
Insulation manufacturer model number
Thermal mass in BTU/°F

Correct answer: Total R-value of the insulation assembly

HERS software uses the total R-value of the insulation assembly to calculate heat flow through the ceiling/attic boundary.

Question 10: In HERS energy modeling, what effect does increasing window-to-floor area ratio have on cooling loads in a hot climate?

It decreases cooling load by admitting more daylight
It generally increases cooling load due to higher solar heat gain (Correct answer)
It has no effect if Low-E glazing is installed
It decreases load because windows have lower thermal mass than walls

Correct answer: It generally increases cooling load due to higher solar heat gain

More window area in a hot climate increases solar heat gain and conductive gain, raising cooling loads even with Low-E glazing.

Question 11: What does 'ACH50' represent in the context of HERS energy modeling?

Air changes per hour at 50 Pascals of pressure differential (Correct answer)
Annual cooling hours when outdoor temperature exceeds 50°F
Airflow capacity of the HVAC system at 50% load
Average ceiling height divided by 50 for ventilation calculation

Correct answer: Air changes per hour at 50 Pascals of pressure differential

ACH50 is the blower door test result expressed as air changes per hour at a 50 Pascal pressure difference, used to characterize envelope airtightness.

Question 12: A modeler is entering a heat pump with a HSPF of 9.0 and a SEER of 16.0. Which value applies to the heating season calculation?

SEER of 16.0
HSPF of 9.0 (Correct answer)
The average of HSPF and SEER
COP derived from SEER only

Correct answer: HSPF of 9.0

HSPF (Heating Seasonal Performance Factor) is the efficiency metric for heat pump heating mode, while SEER applies only to cooling.

Question 13: When a HERS rater inputs conditioned floor area into the software, what spaces should be included?

All floors of the home including the garage and unfinished basement
Only heated areas above grade with finished flooring
All space within the thermal boundary that is heated or cooled (Correct answer)
Exterior decks and porches if they are enclosed

Correct answer: All space within the thermal boundary that is heated or cooled

Conditioned floor area includes all space within the thermal and pressure boundary that is intentionally heated or cooled, regardless of finish or grade level.

Question 14: How does HERS software typically account for thermal mass in a home with concrete block walls?

Thermal mass is ignored in all standard HERS models
Material density and specific heat are used to calculate heat storage capacity (Correct answer)
Thermal mass is approximated by adding R-2 to the assembly R-value
Concrete block walls are modeled identically to wood-frame walls

Correct answer: Material density and specific heat are used to calculate heat storage capacity

HERS software uses the material's density and specific heat capacity to model how concrete block walls store and release heat, affecting peak load timing.

Question 15: A rater is modeling a two-story home where the second floor overhangs the first floor by 2 feet. How does this overhang affect the energy model?

It is ignored because overhangs only matter for windows
It creates an exposed floor assembly that must be modeled with appropriate R-value and area (Correct answer)
It automatically improves the HERS score by reducing infiltration
It is treated the same as a foundation wall in the model

Correct answer: It creates an exposed floor assembly that must be modeled with appropriate R-value and area

A cantilevered floor exposed to outside air must be modeled as a separate exposed floor assembly with its own insulation R-value and square footage.

Question 16: Which HERS software input directly affects the calculated internal gains used in the energy model?

Number of bedrooms (Correct answer)
Roof pitch angle
Exterior wall color
Foundation wall height

Correct answer: Number of bedrooms

RESNET protocols use the number of bedrooms as a proxy for occupant count and appliance loads, which determines internal heat gain inputs.

Question 17: When modeling a gas fireplace in HERS software, what efficiency value is typically entered?

The fireplace's decorative efficiency rating from the manufacturer
The Annual Fuel Utilization Efficiency (AFUE) for the fireplace insert (Correct answer)
Fireplaces are excluded from HERS energy models entirely
A default value of 50% unless a test report is provided

Correct answer: The Annual Fuel Utilization Efficiency (AFUE) for the fireplace insert

Gas fireplace inserts with documented AFUE values are modeled using that efficiency; otherwise RESNET default values are applied.

Question 18: A HERS rater is analyzing a home with both a gas furnace and an electric air conditioner sharing the same duct system. How should this be modeled?

Model only the dominant fuel source and ignore the other
Enter both systems separately, sharing the same duct leakage inputs (Correct answer)
Model as a dual-fuel heat pump with backup resistance heat
Average the efficiency ratings of both systems for a single entry

Correct answer: Enter both systems separately, sharing the same duct leakage inputs

Split HVAC systems are modeled by entering the heating and cooling equipment separately while linking them to the same duct system distribution inputs.

Question 19: What is the significance of the 'heating degree days' (HDD) value used in HERS energy modeling?

It sets the maximum allowable duct leakage for the climate zone
It quantifies the cumulative heating demand of the local climate over a heating season (Correct answer)
It determines the minimum AFUE required for the heating system
It calculates the number of days the home will require supplemental heating

Correct answer: It quantifies the cumulative heating demand of the local climate over a heating season

HDD reflects how cold and how long winters are at the site, directly influencing the magnitude of annual heating energy calculations in the model.

Question 20: In HERS modeling software, what is meant by 'distribution system efficiency' for a forced-air system?

The ratio of blower motor electrical input to airflow output
The fraction of heating or cooling energy delivered to conditioned space after duct losses (Correct answer)
The percentage of time the air handler operates at peak capacity
The efficiency of the air filter in removing particulates

Correct answer: The fraction of heating or cooling energy delivered to conditioned space after duct losses

Distribution efficiency accounts for duct conduction and leakage losses, representing what fraction of the system's output actually reaches the conditioned living space.

Question 21: A rater is modeling a home with an ERV (Energy Recovery Ventilator). Which efficiency rating of the ERV is most important to enter accurately?

Fan motor efficiency (%) at rated airflow
Sensible and latent recovery efficiency (%) (Correct answer)
Minimum outdoor air temperature rating (°F)
MERV rating of the built-in filter

Correct answer: Sensible and latent recovery efficiency (%)

The ERV's sensible and latent recovery efficiencies determine how much energy is recovered from the exhaust air stream, reducing the ventilation heating and cooling load.

HERS Energy Modeling & Analysis

In REM/Rate or equivalent HERS software, what does the 'reference home' represent?

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