InterNACHI HEA cheat sheet

Heat flows only from warmer to colder; the three modes are conduction (through solids), convection (fluid currents), and radiation (electromagnetic, needs no medium).

Conduction steady-state: Q = U × A × ΔT, where Q is Btu/h, U is Btu/(h·ft²·°F), A is ft², and ΔT is °F. R-value = 1/U.

Layered assemblies add resistances: R_total = R_si + R1 + R2 + … + R_se. Series heat flow is limited by the highest-resistance layer, so a thin low-R path controls performance.

U-factors for parallel paths must be area-weighted, not R-weighted: U_avg = (U1·A1 + U2·A2)/(A1 + A2). Framing fraction typically 15–25% of a wood-frame wall area.

Thermal bridging: a 2×6 stud at R-1.0 per inch interrupts cavity insulation; continuous exterior insulation reduces the penalty because it covers framing, not just cavities.

Sensible heat: Q = 1.08 × CFM × ΔT (Btu/h, sea level). Latent heat: Q_lat = 0.68 × CFM × Δgrains (Btu/h). Total = sensible + latent.

Infiltration heat loss is weather- and stack-driven; the simplified load term is Q ≈ 1.08 × CFM_infiltration × ΔT, with CFM from blower door results (CFM50 ÷ N-factor).

Water vapor moves by diffusion (slow, vapor pressure driven) and by air leakage (fast, carries far more moisture). Air sealing precedes vapor control in most mixed and cold climates.

Dew point: the temperature at which air reaches saturation. Surface condensation occurs when a surface temperature falls below the interior dew point; interstitial condensation occurs within the assembly.

Insulation levels are reported as installed R-value; verify grade (Grade I/II/III) and settled thickness, since compressed or gapped batts lose rated R-value.

Air sealing targets the pressure boundary: top plates, rim joists, penetrations, chases, attic hatches, and recessed fixtures. Leakage area scales with the pressure-boundary area, not floor area.

Window labels: U-factor (lower is better), SHGC (lower reduces cooling load), and air leakage (≤0.3 cfm/ft² for ENERGY STAR). NFRC ratings are whole-product values.

A window's effective R-value = 1/U-factor; a U-0.30 window is R-3.3, so replacing windows rarely beats attic air sealing and insulation on cost per unit of saved energy.

Door and window air leakage is often dwarfed by duct leakage and ceiling-plane bypasses; diagnose with a blower door before choosing upgrade scope.

Vapor retarder class is defined by permeance: Class I ≤0.1 perm, Class II 0.1–1.0, Class III 1.0–10. Cold-climate assemblies generally place low-perm material on the warm side.

Rim joists and band joists are common cold spots and condensation sites; air seal with rigid foam plus sealant, and insulate to match the wall assembly.

Knee walls, dormers, and cantilevers create uninsulated or open cavities; verify with IR imaging and confirm the thermal boundary is continuous and aligned with the pressure boundary.

Window and door replacement does not fix air leakage paths in the wall or ceiling plane; treat envelope as a system and verify with post-work blower door data.

Heating equipment efficiency: AFUE = annual useful heat output ÷ annual fuel energy input. Combustion efficiency (stack test) is a single-point measure, not AFUE.

Cooling efficiency: SEER2 and EER2 are the current test-based ratings; HSPF2 covers heat pumps. Higher is better; match equipment size to Manual J load, not rules of thumb.

Refrigerant charge affects capacity and efficiency: a 10% undercharge can cut capacity measurably. Verify superheat/subcooling per manufacturer specs.

Combustion appliance categories: Category I (non-condensing, vent ≥140°F), Category IV (condensing, vent <140°F, PVC). Mismatched venting is a safety and durability failure.

Combustion safety tests: spillage (smoke pencil or flame at draft hood), draft pressure, CO in flue gas (air-free CO), and ambient CO. Air-free CO above 100 ppm warrants investigation; above 400 ppm is a red flag.

CAZ testing: measure worst-case depressurization with doors closed and exhaust fans running; compare to appliance limits (commonly −3 Pa for naturally drafting appliances, −5 Pa for Category I).

Ventilation standards: ASHRAE 62.2 whole-house ventilation rate ≈ 0.03 × floor area (ft²) + 7.5 × (bedrooms + 1) in CFM. Local exhaust for kitchens and baths runs separately.

Balanced ventilation (HRV/ERV) exchanges sensible heat; ERV also transfers moisture. Use ERV in humid cooling climates, HRV in cold dry climates.

Duct location matters: ducts in unconditioned attics can lose 20–30% of delivered energy. Sealing and burying ducts or moving them inside the envelope are high-value measures.

Blower door measures envelope leakage at a reference pressure (typically 50 Pa). Key outputs: CFM50, ACH50 = CFM50 × 60 ÷ conditioned volume (ft³), and CFM50 per ft² of envelope area.

Natural infiltration estimate: ACH_natural ≈ ACH50 ÷ N, where N ranges roughly 10–20 depending on climate and building height (LBL method uses local data).

Duct leakage: total leakage from a duct pressurization test (cfm25), expressed as % of system airflow. Duct leakage to outside requires a house-pressure-compensated test.

Leakage area estimate: ELA (in²) ≈ CFM50 ÷ 10 at 50 Pa for a sharp-edged orifice approximation; use only as a screening number.

Infrared thermography is valid only with a sufficient ΔT (generally ≥10–18°F) and steady conditions; solar gain, wind, and emissivity differences create false anomalies.

Utility bill analysis: normalize by HDD/CDD and floor area; whole-house baseload = total use minus weather-dependent use. Compare EUI (kBtu/ft²/yr) to ENERGY STAR Portfolio Manager benchmarks.

Energy modeling outputs are estimates, not guarantees; document assumptions (weather file, setpoints, occupancy, R-values) and calibrate to measured bills where possible.

Prioritization rule: rank measures by savings per dollar invested, then by health/safety and durability first, then comfort, then carbon. Air sealing and attic insulation usually precede HVAC replacement.

Measure stacking is non-additive: two measures each saving 20% combined save about 36%, not 40%, because savings interact. Model packages, not isolated measures.

Reports should separate measured data (blower door, IR, CO readings), observed conditions, and recommendations with estimated savings and cost basis; label estimates as estimates.

Health and safety findings (spillage, CO, mold, asbestos, knob-and-tube wiring) are reported immediately and take precedence over energy recommendations.

Scope statements must state what was and was not inspected (e.g., no destructive testing, no combustion appliance disassembly) to limit liability.

Program standards vary: BPI, RESNET/HERS, and utility weatherization programs each define test protocols, required forms, and allowable measures. Follow the governing program's standard.

Disclose conflicts of interest: if the auditor or firm also installs the recommended measures, disclose it and keep the audit independent of sales pressure.

Client communication: explain findings in plain language, tie recommendations to the client's stated goals (comfort, cost, health), and provide written next steps.

Data integrity: never fabricate test results or backdate reports. Record instrument calibration dates and test conditions (indoor/outdoor temperature, wind, baseline pressure).

Do not claim certification, affiliation, or ENERGY STAR program participation you do not hold; describe credentials accurately and keep continuing education current.

Psychrometrics: relative humidity is the ratio of actual vapor pressure to saturation vapor pressure at the same temperature; warming air lowers RH without adding moisture.

Moisture balance: wetting (rain, plumbing, vapor diffusion, air transport) versus drying (ventilation, diffusion, drainage). Assemblies must dry in at least one direction.

Stack effect pressure ≈ 0.03 × h × (1/T_out − 1/T_in) in inches of water; taller buildings have stronger natural driving forces.

Wind pressure: P ≈ 0.00256 × V² × Cp (psf, V in mph). Wind and stack effects combine with mechanical fan pressure to set the house pressure field.

Latent heat of vaporization of water ≈ 970 Btu/lb; condensing 1 lb of water vapor releases roughly 1,000 Btu, which is why moisture problems often appear as heat and durability issues.

R-value of air films: interior surface ≈ 0.68, exterior winter ≈ 0.17 (h·ft²·°F/Btu). Ignoring air films overstates assembly R-value.

Degree-day method: annual heat loss ≈ (UA) × HDD × 24 ÷ ΔT_design basis; use HDD from the nearest weather station and adjust for base temperature.

Dense-pack cellulose in closed cavities reaches roughly 3.5–3.8 R per inch; spray foam 3.5–7 R per inch depending on type. Values vary by product; use manufacturer data.

Manual J sizing uses room-by-room loads; Manual S selects equipment; Manual D sizes ducts. Oversizing causes short cycling, poor dehumidification, and higher cost.

Airflow rule: roughly 400 CFM per ton of cooling (range 350–450 depending on climate and latent load). Verify with a flow hood or static pressure traverse.

Static pressure budget: supply plus return external static pressure typically should not exceed 0.5 in. w.c. for residential blowers; high ESP signals undersized ducts or dirty coils.

Heat pump balance point: the outdoor temperature where capacity equals load. Below it, supplemental heat runs; above it, the heat pump alone suffices.

Combustion air: a confined space requires two permanent openings or a known infiltration rate; verify with CAZ test rather than assuming leakage supplies combustion air.

Duct leakage to outside is the metric that matters for energy; leakage into conditioned space affects distribution and pressure but not directly the energy loss.

Ventilation rate control: ASHRAE 62.2 allows credit for infiltration; calculate effective ventilation rate from blower door data, then size the fan to the difference.

Refrigerant leak detection: EPA Section 608 rules require leak repair for appliances above threshold charge within specified timeframes; document refrigerant type and charge.

Blower door calibration: check the manometer zero, fan calibration, and ring configuration; record baseline (house-to-outside) pressure before and after the test.

Pressure pan testing: measure pressure differences across outlets while the blower door runs; higher readings indicate leakier paths. Use for targeted air sealing, not for total leakage.

Duct blaster: measures total duct leakage at 25 Pa; leakage to outside requires a second test with the house at a controlled pressure.

Combustion analyzer: measures O2, CO, CO2, stack temperature, and calculates excess air and air-free CO. Excess air outside 3–9% (natural gas) signals a problem.

Moisture meters: pin-type measures conductivity at the surface; pinless measures capacitance through material. Both are relative indicators; calibrate and interpret by material.

Energy model calibration: compare modeled annual use to weather-normalized bills; a difference within ±10–15% is generally acceptable for program purposes.

Modeling inputs that most affect results: envelope R-values and leakage, HVAC efficiency and distribution losses, thermostat schedules, and internal gains.

Instrument documentation: record model, serial, calibration date, and test conditions for every diagnostic; results without conditions are not defensible.

Weather normalization: use HDD/CDD from the same period as the bills; a 12-month bill history captures seasonal variation better than a single month.

Baseload separation: plot monthly use against HDD/CDD; the y-intercept approximates non-weather use (water heating, appliances, lighting).

EUI = annual site energy (kBtu) ÷ conditioned floor area (ft²). Compare to ENERGY STAR Portfolio Manager medians for the building type and climate zone.

Simple payback = installed cost ÷ annual savings. It ignores measure life and fuel escalation; pair it with lifecycle cost or savings-to-investment ratio (SIR).

SIR = present value of savings ÷ present value of costs. Programs often require SIR ≥ 1.0; higher SIR ranks measures higher.

Measure priority order: health/safety, then building durability (air sealing, moisture control), then envelope, then HVAC, then renewables. Cheap envelope measures usually beat equipment replacement.

Interactive effects: envelope improvements reduce HVAC loads, so HVAC replacement savings shrink. Model the package and re-verify with post-retrofit bills.

Verify savings with a post-retrofit period and normalized comparison; measurement and verification (M&V) closes the loop and supports program claims.

A defensible report includes: scope, methods and instruments, measured data with conditions, observations, health/safety findings, recommendations with basis, and limitations.

Photos and thermal images should include date, time, location, and conditions (indoor/outdoor temperature, wind) so they can be interpreted later.

Client communication: confirm goals before the audit, present findings in plain language, and provide a written summary with prioritized next steps and estimated costs.

Program forms: BPI, RESNET, and utility programs specify required test values and pass/fail thresholds; complete them accurately and keep copies.

Ethics: disclose conflicts of interest, do not upsell unnecessary measures, do not misrepresent certifications, and protect client data.

Liability: state limitations clearly (no destructive testing, no code compliance determination unless contracted) and avoid guaranteeing savings.

Continuing education and certification maintenance are program requirements; lapsed credentials must not be represented as current.

Follow-up: offer a post-retrofit verification visit and document measured improvement (blower door, bills) to support both client trust and program reporting.

Spillage test: with the appliance firing and the CAZ at worst-case depressurization, check for spillage at the draft hood for at least 1–2 minutes after steady-state operation.

Draft measurement: a naturally drafting appliance typically needs −2 to −5 Pa at the vent connector; positive or near-zero draft signals a blocked or undersized vent.

Air-free CO = measured CO × (20.9 ÷ (20.9 − O2 measured)). It corrects for dilution and is the number to compare against limits.

Ambient CO action level: 9 ppm (8-hour average) and 35 ppm (1-hour) are common guidance limits; evacuate and ventilate if exceeded.

Ventilation: ASHRAE 62.2 requires whole-house mechanical ventilation in most new and renovated homes; local exhaust for baths (≥50 cfm intermittent) and kitchens (≥100 cfm intermittent).

Makeup air: large exhaust fans (range hoods >400 cfm) can backdraft appliances; provide makeup air or interlock per code.

Combustion air: verify the appliance has adequate combustion air; a CAZ test with all exhaust fans running reveals whether the appliance can draft safely.

Documentation: record CAZ pressure, spillage results, CO readings, and instrument calibration; these are the defensible record of a safety determination.

Attic insulation: verify depth and settled density; blown cellulose at 3.5 lb/ft³ and fiberglass at ~1.5–2.5 lb/ft³ achieve rated R-value. Check for wind washing and baffles at eaves.

Wall insulation: dense-pack cellulose fills cavities and reduces convection; verify with IR and by checking density at test holes.

Air barrier continuity: trace from attic to foundation; common breaks are at rim joists, chases, and penetrations. A blower door plus IR finds them.

Windows: check for failed seals (fogging), air leakage at operable sashes, and thermal bridging through frames. Low-e coatings and argon fill improve U-factor.

Doors: weatherstripping, sweeps, and thresholds; a blower door with a smoke pencil identifies leakage paths at frames and undercuts.

Knee walls and sloped ceilings: verify insulation contact and air sealing; these are frequent bypasses to unconditioned space.

Foundation: rim joists, sill plates, and crawlspace vents. Sealed and insulated crawlspaces change the pressure boundary and must be modeled accordingly.

Verify with post-work blower door and IR; document before/after CFM50 and ACH50 to demonstrate improvement.

Model inputs: geometry, envelope R-values, infiltration (from blower door), HVAC efficiency, distribution losses, thermostat schedule, and internal gains.

Calibration: adjust infiltration and HVAC efficiency within reasonable ranges to match bills; do not tune inputs outside physical plausibility.

Weather files: use TMY data for the nearest station; microclimate differences (elevation, urban heat island) can shift results.

Savings estimates: report ranges, not single numbers, and state assumptions. Program savings claims require documented methods.

Utility rate structures: tiered, time-of-use, and demand charges change the value of measures; savings in kWh may not equal savings in dollars.

Baseload vs. weather-sensitive use: separating them reveals whether the biggest opportunity is envelope/HVAC or water heating/appliances/lighting.

Measure life: insulation 20–30+ years, HVAC 15–20, windows 20–30; lifecycle cost accounts for replacement timing.

Post-retrofit verification: compare normalized bills and repeat blower door; document actual vs. modeled savings.

Independence: the auditor should not have a financial interest in the recommended measures, or must disclose it clearly.

Accuracy: report only what was measured or observed; label estimates and assumptions. Never fabricate data or backdate reports.

Confidentiality: protect client data and do not share without consent, except as required by program or law.

Competence: stay within scope; refer to specialists (electricians, HVAC technicians, mold remediators) when findings exceed your qualifications.

Transparency: provide written scope, fees, and limitations before the audit; explain what the client will receive.

Respect: communicate findings without alarmism, tie recommendations to client goals, and provide clear next steps.

Program compliance: follow the governing program's protocols and forms; do not claim certifications or affiliations you do not hold.

Follow-up: offer verification and answer questions; document the client's decisions and any declined recommendations.

Blower door setup: seal the door frame, connect the manometer, zero it, and record baseline pressure before installing the fan.

Test protocol: depressurize to 50 Pa, record CFM50, and note conditions (wind, temperature, stack). Multiple-point tests improve accuracy.

ACH50 = CFM50 × 60 ÷ volume. A tight house is often defined as ≤3 ACH50 in cold climates; older homes commonly exceed 10.

Duct blaster: connect to the air handler, seal registers, and pressurize to 25 Pa; record total leakage and, with house compensation, leakage to outside.

IR camera: use with ΔT ≥10–18°F, avoid solar gain, and interpret emissivity differences. Confirm anomalies with a moisture meter or smoke pencil.

Smoke pencil: trace air leakage paths at the pressure boundary; useful for targeted air sealing and client education.

Combustion analyzer: measure O2, CO, CO2, stack temp; calculate excess air and air-free CO. Record calibration date.

Documentation: record instrument model, serial, calibration date, and test conditions for every measurement.

Rank by savings per dollar, then health/safety, durability, comfort, and carbon. Air sealing and attic insulation usually rank high.

Package modeling: account for interactive effects; savings are non-additive and shrink as measures stack.

Cost basis: use installed cost including labor, permits, and any required upgrades (e.g., ventilation when air sealing tightens the house).

Report structure: scope, methods, data, observations, health/safety, recommendations with basis, limitations, and next steps.

Client communication: confirm goals, explain findings in plain language, and provide a written summary with prioritized actions.

Program standards: follow the governing program's protocols, forms, and thresholds; document compliance.

Ethics: disclose conflicts, do not upsell, do not misrepresent credentials, and protect client data.

Verification: offer post-retrofit testing and bill comparison to document actual savings.

Heat transfer modes: conduction (Q = U·A·ΔT), convection (fluid motion), radiation (Q = ε·σ·A·(T1⁴ − T2⁴)).

R-value = 1/U; layered assemblies add R; parallel paths area-weight U-factors.

Air leakage carries both heat and moisture; air sealing is often the highest-value measure.

Psychrometrics: RH depends on temperature; warming air lowers RH without adding moisture.

Dew point and surface temperature determine condensation risk; interstitial condensation depends on vapor pressure and permeance.

Stack and wind drive natural infiltration; mechanical fans change the pressure field and can backdraft appliances.

Moisture balance: assemblies must dry in at least one direction; vapor retarders belong on the warm side in cold climates.

Degree-day method estimates annual heat loss from UA and HDD.

AFUE, SEER2, EER2, and HSPF2 are the efficiency metrics; match equipment to Manual J load.

Airflow: ~400 CFM per ton cooling; verify external static pressure ≤0.5 in. w.c. for residential blowers.

Refrigerant charge affects capacity; verify superheat/subcooling per manufacturer specs.

Combustion safety: spillage, draft, CO, and CAZ testing; air-free CO above 100 ppm warrants investigation.

Ventilation: ASHRAE 62.2 whole-house rate ≈ 0.03 × floor area + 7.5 × (bedrooms + 1) CFM.

HRV vs. ERV: ERV transfers moisture, HRV does not; choose by climate.

Duct location and leakage: ducts in unconditioned space lose 20–30% of delivered energy; seal and bury or move inside.

Makeup air for large exhaust fans prevents backdrafting.

Weather normalization uses HDD/CDD from the same period as the bills; 12 months captures seasonal variation.

Baseload separation: plot use vs. HDD/CDD; the intercept approximates non-weather use.

EUI = annual site energy (kBtu) ÷ floor area (ft²); compare to Portfolio Manager benchmarks.

Simple payback = cost ÷ annual savings; pair with lifecycle cost or SIR.

SIR = present value of savings ÷ present value of costs; programs often require SIR ≥ 1.0.

Model calibration: compare modeled use to normalized bills; ±10–15% is generally acceptable.

Interactive effects: envelope improvements reduce HVAC loads, so equipment savings shrink.

Post-retrofit M&V closes the loop and supports program claims.

Reports separate measured data, observations, and recommendations; label estimates.

Health and safety findings take precedence over energy recommendations.

State scope and limitations clearly (no destructive testing, no code determination unless contracted).

Follow the governing program's protocols and forms; do not claim certifications you do not hold.

Disclose conflicts of interest and keep the audit independent of sales pressure.

Communicate in plain language, tie recommendations to client goals, and provide written next steps.

Protect client data and do not share without consent.

Offer post-retrofit verification and document actual savings.