BPI Building Analyst cheat sheet

Stack effect pressure difference: ΔP = ρ·g·h·(1/T_out − 1/T_in) with T in absolute units; a 10 °F indoor-outdoor difference across a two-story house is roughly 3-4 Pa at the neutral pressure level.

Three transport mechanisms move heat and moisture: conduction, convection (air leakage), and radiation; air leakage typically dominates sensible shell losses at 30-50% in older homes.

Water vapor flows from warm/wet to cold/dry; condensing surfaces occur where temperature falls below the dew point, so air sealing must keep the pressure boundary and thermal boundary aligned.

Thermal boundary, air barrier, and vapor retarder must be continuous and in the correct order; a vapor retarder on the wrong side traps moisture and promotes decay.

R-value is resistance to conductive heat flow (hr·ft²·°F/Btu); U-value = 1/R is conductance, and assembly U-values add in series: U_total = 1/(R1+R2+...+Rfilm).

Dew point of air at 70 °F and 40% RH is about 45 °F; surface temperatures below that value support condensation and mold growth.

Capillary suction, air leakage, and vapor diffusion drive moisture in that order of magnitude; diffusion through most building materials is small compared with air-transported moisture.

Pressure diagnostics use three reference pressures: inside, outside, and the neutral pressure level where inside equals outside; the NPL shifts with stack, wind, and mechanical imbalance.

Blower door test per ASTM E779: establish baseline pressures, install door in an exterior opening, and report CFM50 at 50 Pa reference pressure after correcting for temperature and altitude.

CFM50 to natural infiltration: divide by 20 for an average home (N-factor 15-25), or use ASHRAE 62.2 effective leakage area for ventilation sizing.

ACH50 = (CFM50 × 60) / conditioned volume in ft³; typical pre-weatherization values run 8-20 ACH50, tight homes below 3 ACH50.

Duct leakage test per ASTM E1554: pressurize the duct system to 25 Pa with the house at a known pressure and report CFM25 as a percentage of system airflow.

Pressure pan readings above 1-2 Pa with reference to the house indicate duct leakage to the outside or to unconditioned space.

Infrared imaging requires a minimum indoor-outdoor temperature difference of about 18 °F and steady conditions for at least 3 hours to resolve thermal anomalies.

Calibrate and zero instruments before use: manometers, combustion analyzers, and hygrometers drift; record serial numbers and calibration dates in the test report.

Zone pressure diagnostics use a calibrated fan and reference tube to measure pressure boundaries and estimate the effective leakage area of an isolated zone.

Grade I insulation is uniformly installed with full contact on all six sides; Grade II has minor gaps; Grade III has substantial gaps and compressions that reduce effective R-value.

Compression reduces R-value per inch: fiberglass batt compressed to half thickness retains roughly 60-70% of its nominal R-value.

The top plate, sill plate, band joist, and rim joist are the highest-priority air sealing locations, along with attic access hatches and recessed fixtures.

Attic insulation must maintain a 1-inch clearance around heat-producing fixtures and chimneys unless an approved listed assembly permits contact.

Air barrier materials must be continuous and sealed at penetrations, transitions, and framing intersections; the air barrier and thermal boundary should be coincident.

Window U-factor and SHGC are separate metrics: U-factor governs heat loss, SHGC governs solar gain, and the selection depends on climate zone and orientation.

Insulation depth for a target R-value: depth (in) = target R-value / R-per-inch of the material; loose-fill cellulose is about 3.5 R per inch.

Dense-pack wall insulation requires a minimum installed density of about 3.5 lb/ft³ in a 2x4 cavity to control settling and convection.

Equipment sizing follows ACCA Manual J for load, Manual S for equipment selection, Manual D for duct design, and Manual T for air distribution.

Sensible heat ratio SHR = sensible capacity / total capacity; typical residential cooling SHR is 0.70-0.80, and oversizing raises SHR and shortens runtime.

Refrigerant charge is verified by superheat (fixed orifice) or subcooling (TXV) methods; target subcooling is typically 8-12 °F per manufacturer data.

Airflow target is about 400 CFM per ton of cooling capacity; low airflow causes coil icing, and high airflow reduces latent removal.

Combustion air requirements: 50 ft³ per 1,000 Btu/hr input for an unconfined space, or two openings sized per the applicable code for a confined space.

Heat pump balance point is the outdoor temperature where capacity equals load; supplementary heat engages below that point.

Furnace steady-state efficiency is measured with a combustion analyzer; AFUE accounts for cycling and jacket losses over a heating season.

Duct insulation R-value and sealing at joints, boots, and plenums reduce distribution losses, which can reach 20-30% in unconditioned attics.

Combustion analysis measures O2, CO, CO2, stack temperature, and draft; ambient CO above 35 ppm or undiluted flue CO above 400 ppm (air-free) warrants action.

Draft measurement in the flue should show negative pressure relative to the zone, typically -2 to -5 Pa for natural draft appliances at steady state.

Worst-case depressurization test: close doors and windows, operate all exhaust fans and dryers, then verify the appliance draft remains within the manufacturer's specified range.

Spillage of flue gases into the living space indicates a failed draft; shut down the appliance and correct the cause before returning it to service.

ASHRAE 62.2 whole-house ventilation rate: Q = 0.03 × floor area + 7.5 × (bedrooms + 1) in CFM, with local exhaust of 50 CFM intermittent or 20 CFM continuous for baths.

A naturally drafting water heater needs a properly sized combustion air supply; tight homes with exhaust fans can backdraft it.

Carbon monoxide alarms should be installed on each level and near sleeping areas; CO is produced by incomplete combustion and is undetectable by smell.

Ventilation systems require balancing: measure exhaust and supply flows with a calibrated hood and confirm the net house pressure stays near neutral.

Degree-day method: annual heating energy = (UA × HDD × 24) / (efficiency × ΔT), where UA is the envelope conductance in Btu/hr·°F.

HDD and CDD are computed against a 65 °F balance point by convention; a lower balance point is used for internal-gain-dominated buildings.

Model inputs must include conditioned volume, envelope areas and R-values, window U-factor and SHGC, infiltration, internal gains, and equipment efficiency.

Savings estimates are compared against a calibrated baseline; calibration uses at least 12 months of utility data and targets a mean bias error within ±5%.

Interactive effects matter: air sealing reduces both conduction losses and infiltration, so savings cannot be added linearly across measures.

Simple payback = installed cost / annual savings; it ignores measure life, financing, and escalation, so pair it with life-cycle cost analysis.

Modeling tools include REM/Rate, EnergyPlus, and BEopt; each uses different assumptions, so document the software version and input set.

Weather normalization adjusts consumption to a standard climate year so that pre- and post-retrofit comparisons are valid.

A work scope lists each measure with quantity, location, specification, and installed cost, plus the expected savings and the basis for each estimate.

Priority order for measures: health and safety first (combustion, moisture, mold), then air sealing and insulation, then equipment replacement.

The report should state test-in and test-out values (CFM50, ACH50, duct leakage) so that performance improvement is verifiable.

Client communication includes a written summary of findings, the recommended scope, expected savings range, and a clear statement of what is excluded.

Contracts should specify warranty terms, change-order procedures, and the standard of work; reference the applicable codes and program requirements.

Any measure that changes the building's pressure balance requires a combustion safety check before and after installation.

Photos, moisture readings, and instrument data belong in the report appendix to support findings and defend against disputes.

Post-retrofit verification repeats the diagnostic tests and compares measured results against the modeled savings assumptions.

Sensible heat equation: Q = 1.08 × CFM × ΔT for air at standard conditions, where Q is in Btu/hr.

Latent heat equation: Q_latent = 0.68 × CFM × ΔW, where ΔW is the humidity ratio difference in grains per pound.

Total heat = sensible + latent; the psychrometric chart gives humidity ratio, dew point, enthalpy, and wet-bulb for any air state.

Enthalpy difference between indoor and outdoor air drives total (not just sensible) load on ventilation and infiltration.

Radiant heat transfer follows Q = σ·ε·A·(T1⁴ − T2⁴); surface temperature, not air temperature, governs comfort near windows and cold walls.

Thermal mass shifts and dampens temperature swings; mass inside the insulation is beneficial, mass outside is not.

Pressure-driven moisture transport moves 10-100 times more water vapor than diffusion through the same assembly.

A building's pressure boundary should coincide with its thermal boundary; misalignment creates cold surfaces and condensation risk.

Blower door readings must be corrected to standard conditions: correct for air density using indoor and outdoor temperature and barometric pressure.

Multiple-point blower door testing produces a leakage curve; the exponent n in Q = C·ΔP^n typically falls between 0.6 and 0.75 for residential buildings.

Effective leakage area ELA = CFM50 / 18 for a typical home, expressed in square inches at 4 Pa reference.

Duct leakage as a percentage of system airflow: divide CFM25 by total system CFM and compare against program thresholds (commonly 10-15%).

Manometer reference tubes must be connected to the correct pressure port; reversed tubing yields sign errors that invalidate the test.

Hygrometers should be checked against a saturated salt reference; RH error above ±5% affects moisture diagnosis.

Smoke pencils and theatrical fog trace air leakage paths during a blower door test; infrared confirms the thermal signature.

Record test conditions (indoor and outdoor temperature, wind, baseline pressure) with every measurement because they affect repeatability.

Rim joists and band joists are sealed with rigid foam or spray foam and insulated to the same level as the adjacent wall.

Attic knee walls require an air barrier on the conditioned side and insulation on the unconditioned side, with a continuous top plate seal.

Recessed can lights must be IC-rated and sealed; older non-IC fixtures require a box or cover that maintains clearance.

Chimney chases and flue penetrations need metal flashing and noncombustible sealing, never expanding foam in contact with the flue.

Insulation baffles maintain a 1-inch ventilation channel at the roof deck in vented attics to prevent wind-washing and ice dams.

Spray foam expands 30-100 times its liquid volume; install in lifts per manufacturer limits to avoid trapped moisture and off-gassing.

Air sealing reduces the stack effect, which lowers both heating load and the potential for backdrafting combustion appliances.

Windows with a U-factor of 0.30 or lower and SHGC tuned to orientation reduce both heating and cooling loads in mixed climates.

Static pressure in a residential duct system should stay below about 0.5 in. w.c. total external static pressure; higher values indicate undersized ducts or restrictive filters.

Return air paths must be sized to match supply; a starved return raises static pressure and reduces airflow across the coil.

Refrigerant lines should be insulated on the suction line to prevent condensation and capacity loss.

Combustion efficiency = (stack loss + jacket loss) subtracted from 100%; steady-state efficiency above 80% indicates a condensing or high-efficiency appliance.

Heat pump defrost cycles temporarily reverse the refrigerant flow; supplemental heat engages during defrost to maintain supply temperature.

Thermostat placement away from supply registers, sunlight, and exterior walls prevents short cycling and false readings.

Duct register airflow can be measured with a flow hood; balancing dampers adjust branch flows to design values.

Equipment replacement should be matched to the measured load, not the nameplate of the existing unit, to avoid oversizing.

Air-free CO = measured CO × (20.9 / (20.9 − O2 measured)); this normalizes readings to zero excess air.

A CO reading above 100 ppm air-free in the flue gas indicates a problem requiring service; above 400 ppm requires shutdown.

Combustion air openings for confined spaces: one within 12 inches of the top and one within 12 inches of the bottom of the enclosure.

Exhaust-only ventilation depressurizes the house; it must be balanced with supply air or makeup air to protect combustion appliances.

Heat recovery ventilators (HRV) exchange sensible heat; energy recovery ventilators (ERV) exchange both sensible and latent heat.

The ASHRAE 62.2 ventilation rate assumes the house is not tighter than 0.35 ACH natural; tighter homes require additional mechanical ventilation.

Backdrafting is confirmed with a smoke test or a pressure measurement at the draft hood showing positive pressure relative to the room.

Gas leaks are detected with a combustible gas detector or bubble solution; a leak at any joint requires shutdown and repair.

Manual J load calculation inputs include design temperatures, window areas and orientation, infiltration (ACH natural), internal gains, and duct location.

Design conditions come from ASHRAE Fundamentals or the program's climate data; using the wrong design temperature skews equipment sizing.

Internal gains: about 230 Btu/hr per occupant sensible, plus appliance and lighting gains per the modeling tool's defaults.

Infiltration in models is often entered as ACH natural, derived from CFM50 using an N-factor or the LBL model.

Model calibration compares predicted versus actual consumption monthly; adjust infiltration and equipment efficiency within reasonable bounds.

Interactive effects: reducing infiltration lowers the heating load but also reduces the ventilation benefit, so pair with mechanical ventilation.

Savings uncertainty should be reported as a range, not a single number, to reflect weather and occupancy variability.

Document assumptions in the report so that another analyst can reproduce the model and verify the savings estimate.

Test-in data establish the baseline; test-out data verify performance and support program incentives.

Health and safety measures take precedence over energy measures and must be documented even when outside the energy scope.

Cost-effectiveness screening uses simple payback, savings-to-investment ratio (SIR), or life-cycle cost; SIR above 1.0 indicates cost-effective.

The scope should separate measures by priority tier and state dependencies between measures (for example, air seal before insulating).

Client reports should include a plain-language summary, the technical appendix, and a clear list of assumptions and exclusions.

Program compliance requires specific documentation: BPI or equivalent certifications, test forms, and photo evidence.

Change orders require written client approval before additional work proceeds.

Post-installation walkthrough with the client confirms operation of ventilation, thermostats, and combustion appliances.

Heat flows from warm to cold; in winter, heat leaves through the envelope and enters through the ground, and the direction reverses in summer.

The three modes of heat transfer are conduction (through solids), convection (through fluids and air), and radiation (electromagnetic).

Thermal bridging through framing reduces effective R-value; advanced framing reduces bridging and improves whole-wall performance.

Moisture sources include bulk water, capillary action, air-transported vapor, and diffusion; control bulk water first.

Mold requires moisture, organic food source, and suitable temperature; controlling moisture is the only practical control.

Pressure differences of 1-3 Pa are enough to drive significant air leakage; stack, wind, and fans are the drivers.

Air sealing should be done before insulation so that the thermal boundary is continuous and effective.

Combustion appliances, exhaust fans, and duct systems all interact with house pressure and must be evaluated together.

Blower door test setup: seal all exterior openings except the door, open interior doors, and set the reference tube to the outside.

Baseline pressure readings are taken before the fan runs; a baseline above 2 Pa suggests wind or stack interference.

Test-in and test-out values should be recorded on the same form with the same instrument for valid comparison.

Duct leakage testing requires sealing all registers and connecting the fan to the air handler or a register boot.

Pressure pan testing measures the pressure difference across a register grille relative to the house; values above 1-2 Pa indicate leakage.

Infrared camera emissivity settings affect readings; use tape or a known-emissivity target on reflective surfaces.

Moisture meters measure percent moisture content by weight or pin resistance; readings above 20% in wood indicate risk.

All test results should be reported with the instrument used, calibration date, and test conditions.

Air sealing materials include caulk, spray foam, rigid foam, and housewrap tape; the choice depends on substrate, movement, and temperature.

Sill plates on concrete should be sealed with a sill seal gasket or caulk compatible with concrete.

Penetrations through the top plate, such as wiring and plumbing, must be sealed with foam or caulk.

Attic hatch covers should be insulated and weatherstripped to the same R-value as the attic floor.

Duct boots in unconditioned space should be sealed to the drywall with mastic and insulated.

Vapor retarders are classed by permeance: Class I below 0.1 perm, Class II 0.1-1.0 perm, Class III 1.0-10 perm.

In cold climates, a Class I or II vapor retarder belongs on the warm side of the insulation.

Insulation should fill the cavity completely without gaps or compression; gaps reduce effective R-value disproportionately.

Furnace AFUE is the ratio of annual heat output to annual fuel input; 80% is standard, 90%+ indicates condensing.

Air conditioner SEER2 and heat pump HSPF2 are the current efficiency metrics under the updated test procedures.

Refrigerant types: R-410A and R-32 are common; R-22 is phased out and must not be mixed with other refrigerants.

A TXV maintains a constant superheat; a fixed orifice relies on charge and outdoor temperature.

Heat pump auxiliary heat should be locked out above the balance point to avoid unnecessary resistance heating.

Duct design uses friction rate and equivalent length; Manual D specifies the method and allowable friction rate.

Filters should be sized for low pressure drop; a dirty filter raises static pressure and reduces airflow.

Commissioning includes verifying charge, airflow, temperature split, and static pressure against manufacturer specifications.

Combustion requires fuel, oxygen, and ignition; incomplete combustion produces CO, and excess air dilutes it.

The stoichiometric air-fuel ratio for natural gas is about 10:1 by volume; appliances operate with excess air for safety.

Draft hoods and barometric dampers regulate draft; a blocked flue causes spillage and CO accumulation.

A combustion analyzer should be calibrated and its sensor replaced per manufacturer intervals; O2 sensors degrade over time.

Ventilation systems should be commissioned by measuring flows at each terminal and verifying the net pressure effect on the house.

Bath fans should be rated for the required CFM at the installed static pressure, not just the free-air rating.

Kitchen range hoods above 400 CFM require makeup air in many codes to prevent depressurization.

CO alarm placement follows manufacturer instructions; combination smoke/CO alarms are acceptable where listed.

Modeling software inputs should match the test-in data: measured infiltration, insulation levels, and equipment specifications.

The model should be updated after the retrofit to reflect as-built conditions and verified with test-out data.

Sensitivity analysis identifies which inputs most affect predicted savings; infiltration and equipment efficiency often dominate.

Weather data should come from a typical meteorological year (TMY) dataset for the location, not a single extreme year.

Energy savings estimates should be presented with a range and the assumptions behind the range.

Interactive effects between measures require whole-house modeling rather than measure-by-measure addition.

Model outputs should be checked against utility bills to validate the baseline before reporting savings.

Documentation of model version, inputs, and assumptions supports quality assurance and program review.

The report should state the building's test-in condition, the recommended measures, the expected results, and the basis for each recommendation.

Cost estimates should include labor, materials, permits, and contingency, and should be separated from energy savings claims.

Client education includes thermostat operation, filter maintenance, ventilation operation, and combustion safety awareness.

Warranty and call-back procedures should be explained in writing at project closeout.

Program incentives and financing options should be disclosed accurately, including eligibility requirements.

The scope should identify measures that are not recommended and explain why, so the client understands the trade-offs.

Final documentation includes test-out results, photos, invoices, and warranty information in a single package.

Client sign-off on the completed scope confirms acceptance and supports program quality assurance.