InterNACHI HEA flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Conduction heat flow formula

Q = U × A × ΔT, where Q is Btu/h, U is Btu/(h·ft²·°F), A is ft², and ΔT is °F. R-value is the reciprocal of U.

Area-weighted U-factor

For parallel paths such as framing and cavity, average U-factors weighted by area: U_avg = (U1·A1 + U2·A2)/(A1 + A2). Averaging R-values instead overstates performance.

Sensible heat equation

Q = 1.08 × CFM × ΔT in Btu/h at sea level. The 1.08 constant combines air density, specific heat, and unit conversions for standard air.

Dew point

The temperature at which air reaches saturation and water vapor begins to condense. A surface colder than the interior dew point will collect condensation.

ACH50

Air changes per hour at 50 Pa, calculated as CFM50 × 60 ÷ conditioned volume in ft³. It normalizes blower door leakage to house size.

Effective leakage area

An estimate of the equivalent hole size in the envelope, often approximated as CFM50 ÷ 10 in square inches. Use as a screening number, not a precise measurement.

Pressure pan test

A pressure-difference measurement across outlets while the blower door runs. Higher readings indicate leakier paths and help target air sealing.

Air-free CO

Measured CO corrected for dilution: air-free CO = CO × (20.9 ÷ (20.9 − O2)). It is the number compared against combustion safety limits.

CAZ depressurization limit

Worst-case depressurization in the combustion appliance zone. Naturally drafting appliances commonly require the CAZ to stay above about −3 Pa; Category I appliances about −5 Pa.

Spillage test

With the appliance firing and the CAZ at worst-case depressurization, check for flue gas escaping at the draft hood. Spillage indicates unsafe venting.

AFUE

Annual Fuel Utilization Efficiency: annual useful heat output divided by annual fuel energy input. It accounts for cycling and standby losses, unlike a single-point stack test.

Heat pump balance point

The outdoor temperature where heat pump capacity equals building load. Below it, supplemental heat runs; above it, the heat pump alone meets the load.

ASHRAE 62.2 ventilation rate

Whole-house ventilation ≈ 0.03 × floor area (ft²) + 7.5 × (bedrooms + 1) CFM. Local kitchen and bath exhaust is calculated separately.

HRV versus ERV

Both are balanced ventilation cores. An HRV transfers sensible heat only; an ERV also transfers moisture, which suits humid cooling climates.

Thermal bridging

Heat flow through framing or other low-R paths that bypass cavity insulation. Continuous exterior insulation reduces the penalty because it covers framing, not just cavities.

Window U-factor and SHGC

U-factor measures whole-product heat loss (lower is better); SHGC measures solar heat gain (lower reduces cooling load). NFRC ratings are whole-product values.

Vapor retarder classes

Class I ≤0.1 perm, Class II 0.1–1.0 perm, Class III 1.0–10 perm. Cold-climate assemblies generally place low-perm material on the warm side.

Rim joist air sealing

Rim and band joists are common cold spots and condensation sites. Seal with rigid foam plus sealant and insulate to match the adjacent wall assembly.

Stack effect

Buoyancy-driven pressure difference caused by indoor-outdoor temperature difference and building height. Taller buildings and colder weather increase it.

Latent heat of vaporization

About 970 Btu is absorbed when one pound of water evaporates and released when it condenses. This is why moisture problems often appear as heat and durability issues.

Degree-day method

Estimates annual heat loss from building UA and heating degree days. HDD comes from the nearest weather station and is adjusted for base temperature.

EUI

Energy Use Intensity: annual site energy in kBtu divided by conditioned floor area in ft². Compare to ENERGY STAR Portfolio Manager benchmarks for building type and climate.

Simple payback

Installed cost divided by annual savings. It ignores measure life and fuel escalation, so pair it with lifecycle cost or savings-to-investment ratio.

Savings-to-investment ratio

Present value of savings divided by present value of costs. Programs often require SIR ≥ 1.0, and higher SIR ranks measures higher.

Interactive effects

Savings from stacked measures are non-additive. Two measures each saving 20% combine to about 36%, not 40%, because envelope improvements reduce HVAC loads.

Duct leakage to outside

The portion of duct leakage that escapes the pressure boundary. It is the metric that matters for energy loss; leakage into conditioned space affects distribution and pressure instead.

External static pressure

Supply plus return pressure the blower works against. Residential blowers typically should not exceed 0.5 in. w.c.; higher values signal undersized ducts or dirty coils.

Blower door baseline

The house-to-outside pressure difference measured before installing the fan. Record it before and after the test to correct results for wind and stack effects.

Infrared thermography limits

IR imaging needs a sufficient temperature difference (generally ≥10–18°F) and steady conditions. Solar gain, wind, and emissivity differences create false anomalies.

Combustion analyzer outputs

Measures O2, CO, CO2, and stack temperature, then calculates excess air and air-free CO. Excess air outside roughly 3–9% for natural gas signals a problem.

Report scope statement

A written description of what was and was not inspected, such as no destructive testing or appliance disassembly. It limits liability and sets client expectations.

Conflict of interest disclosure

If the auditor or firm also installs recommended measures, disclose it clearly and keep the audit independent of sales pressure.

Health and safety priority

Findings such as spillage, elevated CO, mold, asbestos, or unsafe wiring are reported immediately and take precedence over energy recommendations.