HERS Cheat Sheet 2026

The 30 highest-yield HERS facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. Which insulation material has the highest R-value per inch, making it useful where space is limited in a HERS-rated home? → Closed-cell spray polyurethane foam
2. Which of the following window characteristics must a HERS rater verify in the field against the plans and specifications? → U-factor and Solar Heat Gain Coefficient (SHGC)
3. Which condition allows a rater to use the 'worst-case' duct leakage value from a prior test on a repeated floor plan? → Sampling protocol approval from the Rating Provider
4. What AFUE rating is the minimum threshold for a gas furnace to be considered high-efficiency under current U.S. energy standards? → 90%
5. What CO concentration threshold (ppm) in undiluted flue gases typically triggers a 'fail' rating during a HERS combustion safety inspection? → 400 ppm
6. Which RESNET/ANSI standard governs water heating energy calculations in HERS ratings? → ANSI/RESNET/ICC 301-2014 (and subsequent amendments)
7. When a HERS rater upgrades a home's insulation from R-11 to R-19 in the walls, what is the expected effect on the HERS Index? → The HERS Index decreases
8. During a blower door test, what effect does a large open fireplace damper have on the result? → It increases the measured CFM50, making the house appear leakier
9. A HERS rater's certification lapses due to missed continuing education requirements. What is the immediate consequence? → The rater cannot perform or submit HERS ratings until recertification is complete
10. What does 'spillage' mean in the context of combustion appliance zone (CAZ) testing? → Combustion byproducts escaping from the draft hood into the living space
11. Orphaned water heaters—left alone on a large flue after a furnace is removed—are at heightened risk of: → Backdrafting because the oversized flue reduces draft velocity
12. 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 generation offsets rated home energy use and can reduce the HERS Index below zero
13. What does a high ELA (Effective Leakage Area) value indicate about a home? → The home has a large equivalent hole size and poor air sealing
14. In HERS rating calculations, on what is the daily domestic hot water consumption estimate primarily based? → Number of bedrooms in the home
15. How does shading impact energy modeling? → Reduces cooling demand
16. 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? → Enter both systems separately, sharing the same duct leakage inputs
17. Which RESNET-recognized testing method allows duct leakage to be measured without pressurizing or depressurizing the entire duct system? → Delta Q method
18. For HERS purposes, what does the 'hot water distribution system efficiency' credit account for? → Energy losses from pipe heat dissipation and water wasted waiting for hot water to arrive
19. What is the purpose of a draft diverter (draft hood) on an atmospheric water heater? → To dilute flue gases with room air and protect the burner from downdrafts
20. Which of the following conditions is most likely to cause backdrafting of a natural draft water heater? → Operation of a powerful, uncompensated kitchen exhaust fan.
21. For HERS rating purposes, when must duct leakage testing be performed during construction? → Before ducts are covered, sealed, or made inaccessible — rough-in stage or final
22. What is the primary purpose of building science in residential construction? → Analyze energy, moisture, and air flow
23. Which factor is most critical when sizing a combustion air opening into a mechanical room containing atmospherically vented appliances? → The BTU input of all appliances combined
24. A HERS rater is verifying a geothermal heat pump installation. Which performance metric is most relevant for its heating mode efficiency? → COP
25. In HERS energy modeling, how is incoming cold water (mains) temperature typically determined? → Location-dependent values based on ground temperature data
26. When testing a atmospherically vented furnace, the CAZ (combustion appliance zone) pressure should ideally read: → Slightly negative or neutral relative to outside
27. In a duct leakage test, what does a very low CFM25 out reading (near zero) with a relatively high CFM25 total reading suggest? → The duct system has significant leaks, all within the conditioned space
28. Which of the following conditions represents a 'worst-case' scenario during a CAZ depressurization test? → All windows and doors closed, all exhaust fans on
29. What role does ventilation play in building science? → Controls indoor air quality
30. Under RESNET policy, how many quality assurance file reviews must a provider conduct per rater per year at minimum? → 1 review per year