BPI HEP Energy Auditor cheat sheet

The house-as-a-system model treats envelope, HVAC, occupants, and pressure/thermal boundaries as coupled; a change to one component shifts airflow, moisture, and combustion safety elsewhere.

Stack effect pressure difference: ΔP = (ρ_out − ρ_in) × g × h; roughly 4 Pa per 3 m (10 ft) of height at 20 °C indoor-outdoor difference, driving infiltration low-to-high in winter.

Sensible heat equation: Q (Btu/h) = 1.08 × CFM × ΔT; latent: Q_latent = 0.68 × CFM × Δgrains, using 4.5 × CFM × Δenthalpy for total load.

R-value is conductive resistance (h·ft²·°F/Btu); U-value = 1/R; assembly U-values add in series, and framing fraction lowers whole-wall R-value below cavity R-value.

Air barrier, vapor retarder, and thermal boundary are distinct control layers; interior vapor retarders belong in cold climates, exterior in hot-humid climates.

Dew point location within an assembly determines condensation risk; vapor drive is high-to-low vapor pressure, typically outward in heating climates and inward in cooling climates.

Natural infiltration reference: ASHRAE 62.2 ventilation rate = 0.03 × floor area (ft²) + 7.5 × (bedrooms + 1) CFM, with infiltration credit applied.

Combustion safety: 50 Pa depressurization limit for atmospherically vented appliances is 5 Pa; spillage or backdrafting requires remediation before air sealing.

Thermal imaging interpretation: cool surfaces in winter indicate conductive or air-leak paths; confirm with blower door or smoke pencil before prescribing work.

Blower door CFM50 converts to natural infiltration using the LBL/ASHRAE factor N ≈ 1/20 to 1/17; ELA (in²) ≈ CFM50 / 10 at 4 Pa reference.

CFM50 per ft² of conditioned floor area benchmarks airtightness: >0.7 high, 0.35–0.7 moderate, <0.35 tight for typical existing homes.

Duct leakage to outside uses a duct blaster plus blower door; subtract house leakage baseline, and target duct leakage ≤10% of system airflow where programs require.

Zone pressure diagnostics map pressure boundaries; a pressure difference across an attic floor indicates a connected leakage path, and gauges resolve hidden pathways.

Combustion analysis measures CO, CO2, O2, stack temperature, and draft; steady-state CO above ~100 ppm air-free in flue gas signals a problem requiring service.

CAZ testing: measure worst-case depressurization with doors closed and exhaust fans running; >5 Pa with natural-draft appliances triggers mitigation.

Infrared survey requires ≥10–15 °C (18–27 °F) indoor-outdoor ΔT and steady conditions; scan interior in heating season and exterior in cooling season.

Moisture measurement: pin meters read wood percent moisture content, pinless read relative; wood above 20% MC is at risk for decay and mold.

Airflow verification: measure static pressure across the air handler and fan curve, or use a flow hood/balometer; a dirty filter or coil raises static and drops delivered CFM.

Degree-day method: annual heating energy (Btu) = UA × HDD × 24 × 1/ΔT_reference; use base 65 °F for HDD and CDD unless a balance point is known.

UA (Btu/h·°F) is the sum of area × U-value across envelope components; fuel-normalized UA can be back-calculated from utility bills and HDD.

Utility bill analysis: normalize by HDD/CDD, compare year over year, and separate base load (non-HVAC) from weather-dependent load.

Simple payback (years) = installed cost / annual savings; combine with SIR or NPV when incentives or fuel escalation alter the economics.

Prioritization hierarchy: health and safety > building durability and moisture > envelope and air sealing > HVAC and distribution > controls and renewables.

Marginal savings diminish; model improvements cumulatively because air sealing changes infiltration and reduces load on HVAC sizing.

Energy savings from envelope improvements scale with ΔT and HDD, so cooling-dominated and heating-dominated climates rank measures differently.

Verify assumptions: use measured blower door, duct leakage, and combustion data rather than defaults; default values inflate or deflate savings in modeling.

Work scope must state measure, quantity, specification, and sequencing; each measure should reference a standard or manufacturer requirement.

ASHRAE 62.2 sets whole-building ventilation and local exhaust rates; BPI and IECC reference it for ventilation compliance after air sealing.

BPI standards require combustion appliance safety testing before and after work when air sealing or pressure changes affect the CAZ.

Client communication: document existing conditions, test-in results, and recommendations in writing; obtain informed consent for measures with health or cost tradeoffs.

Contractor scope should separate must-do health and safety items from optional efficiency upgrades, with clear pricing and warranty terms.

Air sealing scope must specify allowable materials and locations, and exclude areas near atmospherically vented appliances unless safety-tested.

Quality assurance: post-work blower door, duct leakage, and combustion testing verify performance; compare to test-in values and report percent improvement.

Change orders should be documented when field conditions differ from the audit; never silently substitute materials or delete safety measures.