22 Blower Door & Ventilation Practice Questions & Answers

1. 1. A blower door test is run on a single-family house. What does the number the test produces actually describe?

   • A.The natural infiltration rate the house experiences during typical winter weather
   • B.The heat lost through the enclosure by conduction over the whole heating season
   • C.The exact location and size of every individual leak in the building enclosure
   • D.The airflow moving through the enclosure at an induced, measured pressure difference✓ Answer

   The fan creates and holds a known pressure difference across the enclosure, and the measured flow needed to hold it is the leakage metric. Natural infiltration, individual leak locations, and conductive heat loss are separate quantities the test cannot report on its own.

   Source: ANSI/BPI-1200-S 10.2 (enclosure air leakage determined by fan pressurization per ASTM E779)Report a problem with this question

2. 2. Enclosure leakage is reported as flow at an elevated reference pressure rather than at the pressures the house sees naturally. Why is the test run that way?

   • A.Because blower door fans can be calibrated to move air only at that one pressure
   • B.Because leakage measured at natural pressure would overstate the tightness of the house
   • C.Because that pressure matches what a house experiences during an average windy winter day
   • D.Because a strong induced pressure swamps wind and stack effects, so results repeat✓ Answer

   Natural pressures from wind and stack effect are small, variable, and constantly changing, so a flow measured under them would not repeat. Driving the house to a much larger reference pressure makes those natural forces a minor share of the total and yields a result another technician can reproduce.

   Source: ASTM E779 / ANSI/BPI-1200-S 10.2 (fan pressurization at an elevated reference pressure)Report a problem with this question

3. 3. Two houses each test at 2,400 CFM50, but one encloses twice the volume of the other. What does this show about the two ways of reporting the result?

   • A.CFM50 gives total flow and ACH50 relates it to volume, so the smaller house is leakier for its size✓ Answer
   • B.Both metrics rank the two houses the same, because volume cancels out of the ACH50 calculation
   • C.ACH50 gives the total flow and CFM50 relates it to volume, so the larger house is leakier for its size
   • D.Neither metric can compare the houses, because leakage compares only at natural pressure

   CFM50 is an absolute flow, so identical readings mean the two houses pass the same air. ACH50 divides that flow by the volume it has to change, so the smaller house turns its air over twice as fast and is the leakier enclosure once size is accounted for.

   Source: ANSI/BPI-1200-S 10.2 (ACH50 = CFM50 x 60 / conditioned volume)Report a problem with this question

4. 4. A blower door test gives 2,700 CFM50 and the volume inside the air barrier is 21,600 cubic feet. Using ACH50 = (CFM50 x 60) / volume, what is the result?

   • A.3.75 air changes per hour
   • B.7.5 air changes per hour✓ Answer
   • C.0.125 air changes per hour
   • D.12.5 air changes per hour

   2,700 x 60 = 162,000 cubic feet per hour, and 162,000 / 21,600 = 7.5 air changes per hour at the reference pressure. Leaving out the factor of 60 gives 0.125 and is the most common slip on this conversion.

   Source: ANSI/BPI-1200-S 10.2 (ACH50 conversion)Report a problem with this question

5. 5. A work scope sets a post-retrofit target of 3.0 ACH50 for a house whose volume inside the air barrier is 20,000 cubic feet. What blower door reading corresponds to that target?

   • A.333 CFM50 at the reference pressure
   • B.6,667 CFM50 at the reference pressure
   • C.60,000 CFM50 at the reference pressure
   • D.1,000 CFM50 at the reference pressure✓ Answer

   Rearranging the conversion gives CFM50 = ACH50 x volume / 60, so 3.0 x 20,000 / 60 = 1,000 CFM50. Multiplying without dividing by 60 produces 60,000, and dividing the volume by 3 or by 60 alone produces the other two values.

   Source: ANSI/BPI-1200-S 10.2 (ACH50 conversion, solved for CFM50)Report a problem with this question

6. 6. A report states that a single-point blower door test was performed. What does that result give you compared with a multi-point test?

   • A.It is valid only for pressurization, while a multi-point test is the only way to depressurize
   • B.It yields one flow at a single pressure, while a multi-point test derives a leakage curve✓ Answer
   • C.It must always be doubled to correct for wind, while a multi-point test needs no correction
   • D.It yields the leakage curve directly, while a multi-point test only averages several readings

   A single-point test holds the house at one reference pressure and records the flow, which is enough for a leakage rate and for the infiltration credit where the authority allows it. A multi-point test records flow at several pressures so the relationship between pressure and flow can be fitted.

   Source: ANSI/BPI-1200-S 10.2 (single-point test acceptable for Q50 where the AHJ permits)Report a problem with this question

7. 7. You are setting up a valid whole-house depressurization test. Which set of conditions is correct?

   • A.Exterior doors and windows closed, interior doors open, and combustion appliances not firing✓ Answer
   • B.Exterior doors closed, attic hatch and crawl vents taped shut, and the water heater firing
   • C.Exterior doors and windows closed, interior doors closed, and the furnace running to circulate air
   • D.Windows open on the leeward side, interior doors open, and the clothes dryer running on high

   The enclosure must be sealed to the outdoors while the conditioned space is opened up so the whole volume sits at one pressure, and combustion appliances must be off so the fan cannot pull flue gases into the house. Taping intentional openings in the boundary or running exhaust equipment corrupts the measurement.

   Source: ANSI/BPI-1200-S 10.2 / ASTM E779 test preparationReport a problem with this question

8. 8. You arrive to test a house with a fire burning in a woodstove and loose ash in an open fireplace. What must happen before the blower door test?

   • A.Test with the fire burning but open a window near the stove to relieve the pressure
   • B.Pressurize the house instead, so that smoke and ash are pushed out through the chimney
   • C.Leave the fire burning, close the stove damper, and depressurize the house as usual
   • D.Put the fire out, let it cool, contain the loose ashes, and test the house only afterward✓ Answer

   Depressurizing the house pulls smoke, embers, and ash out of the appliance and into the living space, which is both a health hazard and a fire hazard, and pressurizing under those conditions is not recommended either. The only safe sequence is to extinguish, cool, and secure the ashes first.

   Source: ANSI/BPI-1200-S 10.2 (fires extinguished before enclosure leakage testing)Report a problem with this question

9. 9. On a gusty day the baseline pressure swings widely before the fan is started and the readings will not settle. What is the correct handling of that test?

   • A.Record the conditions and baseline, treat the result as uncertain, and retest when calm✓ Answer
   • B.Average two unstable readings and report the mean as the final enclosure leakage rate
   • C.Report the highest reading seen, since wind can only reduce the measured leakage rate
   • D.Subtract a fixed wind correction from the reading and report the result as accurate

   An unstable baseline means the pressure the fan is working against is not known, so the derived flow carries an error the technician cannot quantify. Documenting the conditions and repeating the test when the weather settles is what keeps the reported number defensible.

   Source: ANSI/BPI-1200-S 10.2 / ASTM E779 (baseline pressure measurement and documentation of test conditions)Report a problem with this question

10. 10. In cold weather a two-story house shows warm air leaving through ceiling penetrations and cold air entering at the rim joist. Where is the neutral pressure plane and what does that mean for sealing priority?

    • A.At the ceiling, so only leaks in the basement floor are worth sealing in winter
    • B.Between them, so the leaks farthest above and below it move the most air and rank first✓ Answer
    • C.Wherever the largest hole is, so the height of a leak never changes the priority
    • D.At the floor, so only leaks in the roof deck see a pressure difference in winter

    Warm air is buoyant, so it exits high and is replaced low, and the level where inside and outside pressures are equal sits between the two. Pressure difference grows with distance from that level, so the highest and lowest leaks move the most air and give the largest reduction when sealed.

    Source: Building science: stack effect and neutral pressure plane; ANSI/BPI-1200-S 10.5.1 (prioritizing leakage paths)Report a problem with this question

11. 11. With the blower door running, what is the most reliable way to find and rank individual leakage sites?

    • A.Pressurize the house and scan the exterior with infrared, since inside surfaces stay uniform
    • B.Depressurize the house and read the fan gauge alone to see which side of the house leaks
    • C.Depressurize the house and trace inward air movement at suspect spots with smoke or by hand✓ Answer
    • D.Shut the fan off and scan interior surfaces with infrared, since airflow masks the patterns

    Depressurizing forces outdoor air inward through every hole at once, so leaks announce themselves as moving air that can be felt, seen with smoke, or read as wash patterns on an infrared scan of interior surfaces. The fan gauge reports only the whole-house total and locates nothing.

    Source: ANSI/BPI-1200-S 10.5.1 (locating and prioritizing major leakage areas with the blower door running)Report a problem with this question

12. 12. The house is held at 50 Pa with respect to outdoors and a gauge reads a 45 Pa difference between the attic and the house. What does that tell you about the boundary?

    • A.The ceiling has no air barrier at all, so the attic and the house behave as one single zone
    • B.Most of the pressure drop is across the roof, so the attic lies inside the pressure boundary
    • C.The attic is sealed from both the house and outdoors, so no conclusion can be drawn here
    • D.Most of the drop is across the ceiling, so the attic lies outside the pressure boundary✓ Answer

    Of the 50 Pa total, 45 Pa is lost across the ceiling and only about 5 Pa across the roof, which means the ceiling is doing the air-barrier work and the attic communicates freely with outdoors. A zone that tracks outdoor pressure sits outside the pressure boundary.

    Source: Zone pressure diagnostics; ANSI/BPI-1200-S 10.5.1.3 (locating the pressure boundary)Report a problem with this question

13. 13. With the house at 50 Pa, gasketed pressure pan readings at four supply registers are 0.3, 0.5, 5.8 and 0.4 Pa. The protocol in use calls for duct sealing above 3 Pa. What do the data indicate?

    • A.The register at 5.8 Pa serves a run leaking to outside the boundary, so recommend duct sealing✓ Answer
    • B.All four registers fail, because pan readings are judged against the 50 Pa house pressure
    • C.No conclusion is possible, because a pressure pan reads supply airflow rather than leakage
    • D.The register at 5.8 Pa serves the tightest run, since a high pan reading means little connection

    A pressure pan reads the pressure the duct holds relative to the depressurized house, so a near-zero reading means the run is sealed from outdoors and a high reading means that run is connected to a space outside the boundary. Only the 5.8 Pa register exceeds the stated trigger.

    Source: ANSI/BPI-1200-S 11.6.2 (qualitative pressure pan test with a blower door)Report a problem with this question

14. 14. After air sealing, the post-work blower door result is well below the tightness level at which the standard in use requires whole-house ventilation. What does the analyst do?

    • A.Reverse part of the air sealing until the house leaks enough to meet the requirement
    • B.Take no action, since air measured at 50 Pa is not the air the house actually receives
    • C.Specify a whole-house ventilation system sized by the calculation and verify its flow✓ Answer
    • D.Advise the occupants to open windows every day, which meets the whole-building requirement

    Tightening the enclosure removes the accidental outdoor air the occupants were relying on, and the fix is deliberate mechanical ventilation, not deliberate leakage. Occupant window operation is not a controlled supply, so the required rate is met by a sized system whose delivered flow is then measured.

    Source: ANSI/BPI-1200-S 8 and Annex I (whole-building ventilation required with enclosure tightening)Report a problem with this question

15. 15. A house has 2,000 square feet of conditioned floor area and 3 bedrooms. Using the whole-building rate Qtot = (0.03 x floor area) + 7.5 x (bedrooms + 1), what is Qtot?

    • A.50 CFM of whole-building airflow
    • B.82.5 CFM of whole-building airflow
    • C.97.5 CFM of whole-building airflow
    • D.90 CFM of whole-building airflow✓ Answer

    The floor-area term is 0.03 x 2,000 = 60 CFM and the occupancy term is 7.5 x (3 + 1) = 30 CFM, for a total of 90 CFM. Using the bedroom count without adding one gives 82.5, and using an older 0.01 coefficient gives 50.

    Source: ASHRAE 62.2-2013 4.1.1 (Qtot), referenced by ANSI/BPI-1200-S Annex IReport a problem with this question

16. 16. The infiltration credit is Qinf = 0.052 x Q50 x S x wsf. The final blower door result is 1,800 CFM50, the two-story factor S is 1.32, and the weather and shielding factor is 0.55. What is Qinf?

    • A.68 CFM of infiltration credit✓ Answer
    • B.94 CFM of infiltration credit
    • C.51 CFM of infiltration credit
    • D.124 CFM of infiltration credit

    0.052 x 1,800 = 93.6, times 1.32 gives 123.6, times 0.55 gives about 68 CFM. Dropping the story factor yields 51, dropping the weather and shielding factor yields 124, and stopping after the first multiplication yields 94.

    Source: ASHRAE 62.2-2013 4.1.3 (infiltration credit), referenced by ANSI/BPI-1200-S Annex IReport a problem with this question

17. 17. For the same house the whole-building rate is 90 CFM and the infiltration credit is 68 CFM. The standard in use says no additional whole-house system is needed if the required fan flow falls below 15 CFM. What is the finding?

    • A.68 CFM of fan flow is required, because the infiltration credit is what the fan must supply
    • B.158 CFM of fan flow is required, because the two rates are added rather than subtracted
    • C.22 CFM of fan flow is required, so a whole-house ventilation system must be specified✓ Answer
    • D.No fan is required, because the infiltration credit already exceeds the total ventilation rate

    Required fan flow is the whole-building rate minus the infiltration credit, so 90 minus 68 leaves 22 CFM. That is above the cutoff the stem supplies, so a whole-house system must be included in the scope and its delivered flow verified after installation.

    Source: ASHRAE 62.2-2013 4.1 (Qfan = Qtot - Qinf), referenced by ANSI/BPI-1200-S Annex IReport a problem with this question

18. 18. A house needs an average of 45 CFM of whole-house ventilation. The installed fan moves 90 CFM and its control cycles well within the maximum interval the standard allows. How long must it run each hour?

    • A.30 minutes each hour, because delivered flow equals rated flow times the fraction of run time✓ Answer
    • B.45 minutes each hour, because the required flow in CFM converts directly into run minutes
    • C.60 minutes each hour, because any fan rated below 100 CFM must run without being switched off
    • D.20 minutes each hour, because a three-hour cycle allows one third of the needed run time

    Intermittent operation is judged by the average delivered flow, which is the rated flow multiplied by the fraction of time the fan runs. A 90 CFM fan running half of each hour delivers an average of 45 CFM, provided the cycle repeats within the interval the standard allows.

    Source: ASHRAE 62.2-2013 4.4 (intermittent whole-building ventilation), referenced by ANSI/BPI-1200-S Annex IReport a problem with this question

19. 19. A tightened house has an atmospherically vented water heater inside the pressure boundary. Which whole-house ventilation strategy best suits that condition, and why?

    • A.A balanced system, because it moves equal air in and out and does not depressurize the house✓ Answer
    • B.An exhaust-only system, because it is the only strategy that filters the outdoor air entering
    • C.A supply-only system, because pressurizing the house pushes flue gases back down the vent
    • D.An exhaust-only system, because the slight depressurization draws combustion air to the heater

    An exhaust-only fan puts the house at a negative pressure, and a naturally drafting appliance competes with that fan for the same air, which can pull flue gases back into the living space. A balanced system supplies and exhausts equal amounts, so it meets the ventilation rate without shifting house pressure.

    Source: ANSI/BPI-1200-S 8 (acceptable ventilation systems) and combustion appliance interaction with house pressureReport a problem with this question

20. 20. An owner asks what the difference is between a heat recovery ventilator and an energy recovery ventilator. What is the correct explanation?

    • A.An HRV transfers heat and moisture, while an ERV transfers only heat between the streams
    • B.An HRV works only in the heating season, while an ERV works only in the cooling season
    • C.An HRV mixes the two air streams, while an ERV keeps the two streams entirely separate
    • D.An HRV transfers heat between the air streams, while an ERV transfers both heat and moisture✓ Answer

    Both are balanced systems whose cores exchange energy between the incoming and outgoing streams without mixing them; the difference is what crosses the core. An HRV moves sensible heat only, while an ERV also moves water vapor, which affects how much indoor humidity is carried out or retained.

    Source: ANSI/BPI-1200-S 8 (heat recovery and energy recovery ventilators as acceptable systems)Report a problem with this question

21. 21. A bath fan labeled 80 CFM is offered by the owner as the whole-house ventilation system. A flow hood at the grille reads 22 CFM. How should the analyst treat this system?

    • A.Credit the average of the two values, since flow hoods routinely under-read by about half
    • B.Credit only the measured flow, and investigate the duct run and termination for restriction✓ Answer
    • C.Credit the rated flow, since the certified label takes precedence over one field reading
    • D.Credit nothing and replace the fan, since a fan below its rating cannot be repaired at all

    A label rating is a laboratory value measured on a test rig, while the house is entitled only to the air the fan actually delivers through its installed duct and termination. The 58 CFM shortfall points to a restriction such as flex duct kinks, long runs, lint, or a stuck backdraft damper.

    Source: ANSI/BPI-1200-S 8 and Annex I (measured airflow of existing fans; post-install airflow testing)Report a problem with this question

22. 22. Enclosure air sealing is planned in a house whose furnace and water heater are atmospherically vented and sit inside the pressure boundary. What does the work scope require?

    • A.Test combustion safety after the work only if a new exhaust fan is installed
    • B.Test combustion safety only before the work, since sealing cannot change venting
    • C.Skip combustion safety testing when the appliances are newer than the measures
    • D.Test combustion safety before the work and repeat the testing after sealing is done✓ Answer

    Reducing enclosure leakage removes the make-up air a naturally drafting appliance depends on, so an appliance that vented acceptably before the work can spill afterward. Testing on both sides of the work is what proves the house was not made unsafe by tightening it.

    Source: ANSI/BPI-1200-S 7 and 10 (combustion safety testing before and after enclosure air sealing)Report a problem with this question

Practice questions based on the BPI Building Analyst Professional exam blueprint, the ANSI/BPI-1100-T home energy auditing standard, the ANSI/BPI-1200-S standard practice, and building science fundamentals. This site is not affiliated with or endorsed by the Building Performance Institute. Combustion appliance zone depressurisation limits, carbon monoxide action levels, draft pressures, spillage times, ventilation rates and air-change targets come from the version of the standard in force for your certification and from the manufacturer's instructions — never from a practice test. The BA-P requires the Building Analyst Technician certification, which in turn requires the Building Science Principles certificate; confirm current eligibility, prerequisites and exam requirements with BPI before you test. About BPI certification →