CRES cheat sheet

Heat moves by conduction (solid contact), convection (fluid/air movement), and radiation (electromagnetic); a building assembly rarely resists all three equally.

R-value measures conductive resistance only; it does not account for air leakage, thermal bridging, or radiant gains.

The stack effect drives warm air up and out of the top of a building in winter; neutral pressure plane is where indoor and outdoor pressure are equal.

Water vapor moves by diffusion (through materials, driven by vapor pressure difference) and by air transport (with bulk air leakage); air transport typically moves far more moisture.

Dew point is the temperature at which air reaches saturation; condensation forms on surfaces at or below dew point.

Thermal bridge is a path of higher conductance through an assembly; it lowers effective R-value below the nominal cavity R-value.

Pressure, temperature, and moisture are coupled: a wall that is airtight on both sides can still trap moisture if the wrong side is vapor retardant for the climate.

Latent heat is energy absorbed or released during phase change without temperature change; sensible heat changes dry-bulb temperature.

Whole-building performance depends on the interaction of envelope, air barrier, vapor control, and mechanical systems; fixing one layer can shift the failure point to another.

Blower door test measures envelope air leakage; report CFM50 and normalize to ACH50 = (CFM50 x 60) / conditioned volume in cubic feet.

CFM50 to natural infiltration conversion uses the LBL/n-factor method: natural CFM approx CFM50 / N, where N typically ranges about 15-20 for average climates and shielding.

Duct leakage testing (e.g., duct blaster) measures leakage to outdoors or total duct leakage; total leakage includes leaks to conditioned space.

Pressure pan testing reads pressure difference across a register while the house is depressurized; higher readings indicate greater leakage connection to the zone.

Infrared thermography reveals surface temperature differences; it requires a steady delta-T (typically 10-18 F or more) and must be interpreted with air leakage and emissivity in mind.

Zonal pressure diagnostics compare pressure between zones to locate dominant leakage paths and estimate effective leakage area.

Combustion safety testing includes draft measurement, spillage check, and CO measurement in the flue and ambient air; spillage of flue gases is a fail condition.

Energy assessment reports prioritize by cost-effectiveness and safety; health and safety findings take precedence over efficiency upgrades.

Baseline data collection includes utility bills, building dimensions, insulation levels, window types, and appliance inventory before any modeling.

Nominal R-value is the labeled insulation value; installed or effective R-value is lower due to compression, gaps, thermal bridging, and convection within the cavity.

Insulation must be in substantial contact with an air barrier on at least one side and enclosed on all six sides to perform near its rated value.

Grade I, II, and III installation quality (RESNET) describes how completely the cavity is filled and how well the insulation contacts the air barrier; grading lowers effective R-value.

Vapor retarder class: Class I (<=0.1 perm, e.g., sheet polyethylene), Class II (0.1-1.0 perm, e.g., kraft-faced or some vapor-retarder paints), Class III (1.0-10 perm, e.g., latex paint).

In cold climates, the vapor retarder goes on the warm-in-winter (interior) side; in hot-humid climates, avoid interior vapor barriers and use exterior vapor-permeable assemblies.

Attic insulation should be installed over a continuous air barrier and maintain ventilation clearance at the eaves; baffles protect the ventilation channel.

Rim joists, band joists, and cantilevers are high-leakage, high-bridging locations that require air sealing plus insulation.

Windows: U-factor measures whole-window conductance (lower is better); SHGC measures solar heat gain fraction (lower reduces cooling load); air leakage and condensation resistance are separate ratings.

Roof and wall assemblies should dry in at least one direction; adding impermeable layers on both sides of a cavity creates a moisture trap.

Heating and cooling load calculations (Manual J or equivalent) must precede equipment selection; oversized equipment causes short cycling, poor dehumidification, and higher energy use.

Equipment sizing uses design conditions and the calculated load; do not size to nameplate of the old unit or to rule-of-thumb square footage.

Duct design: total external static pressure must be within the blower's rated range; excessive static pressure reduces airflow and can ice coils or trip limits.

Airflow target for typical residential cooling is roughly 350-400 CFM per ton of capacity; low airflow causes coil icing and high supply temperatures.

Refrigerant charge must be verified by superheat or subcooling per manufacturer method; undercharge and overcharge both reduce capacity and efficiency.

Combustion appliances need adequate combustion air; a confined space requires two permanent openings sized per code or a ducted outdoor air supply.

Heat pump balance point is the outdoor temperature at which heat pump capacity equals building load; below it, auxiliary heat runs.

Duct location matters: ducts in unconditioned attics lose or gain significant energy; sealing and insulating ducts or moving them inside the envelope improves efficiency.

Ventilation: ASHRAE 62.2 sets whole-house ventilation rates; exhaust-only, supply-only, and balanced (HRV/ERV) strategies differ in pressure effects and energy recovery.

The air barrier must be continuous, durable, and in contact with insulation; the vapor retarder is separate and its location depends on climate.

Air sealing priority order: attic plane (top of house), rim joists and band joists, penetrations through the envelope, then windows and doors.

Chimney chases, dropped soffits, and balloon-frame cavities are major hidden leakage paths that connect conditioned space to attic or exterior.

Can lights, bath fans, and dryer vents must be sealed and, where penetrating the envelope, must not create a moisture path into the cavity.

Bulk water control is the first defense: roof, flashing, drainage, and grading; vapor control and air sealing come after bulk water is managed.

Wet basements: manage exterior water first (grading, downspouts, footing drains); interior vapor barriers on the wrong side can trap moisture in the slab or wall.

Crawlspace encapsulation converts a vented crawlspace to a conditioned, sealed space; it requires a ground vapor barrier, sealed vents, and often a supply or dehumidifier.

Bath and kitchen exhaust must terminate outdoors, not into attic or crawlspace; backdraft dampers and short, smooth duct runs reduce moisture and pressure problems.

In hot-humid climates, interior air leaking into wall cavities can condense on cool surfaces; air sealing the interior side reduces this risk.

Carbon monoxide (CO) is a colorless, odorless gas from incomplete combustion; symptoms include headache, nausea, dizziness, and fatigue; it is a life-safety hazard.

Combustion safety order of operations: verify draft, check for spillage, measure CO in flue and ambient air, and confirm combustion air before any tightening of the envelope.

Atmospheric (natural draft) appliances are the most vulnerable to depressurization from exhaust fans, dryers, and blower door testing; induced-draft and sealed-combustion units are safer.

Depressurization limits: combustion appliance zone (CAZ) testing checks whether exhaust fans can depressurize the zone enough to backdraft appliances.

Radon is a radioactive soil gas that enters through foundation cracks and openings; test before and after air sealing; mitigation uses sub-slab depressurization.

Moisture and mold: indoor relative humidity should generally be kept below about 50-60% in cooling season to limit mold growth; fix the water source first.

Ventilation with filtration (MERV-rated filters) reduces particulates; high-MERV filters increase static pressure and may require blower adjustment.

Asbestos and lead paint are hazards in older homes; disturb them only with proper precautions and certified abatement where required.

CO alarms should be installed near sleeping areas and on each level; test and replace per manufacturer instructions.

Energy models compare proposed upgrades against a baseline; savings estimates depend on accurate inputs for envelope, equipment, and occupancy schedules.

Model calibration compares predicted energy use to utility bills; a common target is within about 10% of annual consumption.

Degree-day method estimates heating or cooling energy from the difference between indoor and outdoor temperature integrated over the season.

RESNET HERS Index: 100 equals a reference new home of the same size and shape; lower is better; a HERS Index of 0 is a net-zero-energy home.

Energy Star for Homes requires third-party verification and a HERS Index threshold that tightens over program versions; check current version requirements.

Building codes (IECC) set prescriptive or performance paths; the performance path uses whole-building energy modeling to trade off measures.

Weatherization programs (e.g., WAP) prioritize cost-effective measures and require health and safety inspections before efficiency work.

Program standards define allowable measures, required documentation, and quality control; failing inspection can require rework and may affect payment.

Utility bill analysis: normalize for weather using heating and cooling degree days and separate base load from seasonal load.

Scope of work should list each measure, quantity, location, and expected outcome, plus exclusions and assumptions.

Explain findings in plain language: describe the problem, the evidence (test results), the recommended fix, and the expected benefit.

Cost-effectiveness is presented as savings versus installed cost; simple payback = installed cost / annual savings.

Informed consent: customers should understand health and safety findings, limitations of testing, and that savings are estimates, not guarantees.

Prioritize safety and durability measures before comfort and efficiency measures in the written scope.

Document baseline conditions and pre-work test results so post-work verification can demonstrate improvement.

Set expectations on timelines, access, dust and disruption, and inspection requirements; confirm who is responsible for permits.

Avoid technical jargon in customer-facing reports; define terms like ACH50, R-value, and HERS Index in one sentence each.

Change orders should be written and signed when scope changes during the job; verbal changes create disputes.