Indoor Air Quality Assessment Visit

Purpose

An IAQ visit produces a measured, dated baseline of what the air in that house is doing and a written finding that names a cause. It does not produce a product recommendation, and the order matters: a shop that walks in and sells a purifier can never show the complaint got better, because it never wrote down what the complaint was. The second failure mode is quieter and worse. A house whose complaint is morning headaches gets an air cleaner and keeps its spilling water heater, and the ventilation equipment sold against the symptom makes the spillage worse.

Scope

Covers the assessment visit on residential and small light commercial systems: arrival screening, occupant interview, outdoor and indoor measurement, ventilation rate assessment, a combustion appliance zone depressurization test, filtration and distribution inspection, moisture observations, and the findings conversation.

Does not cover the remediation that follows, does not cover sampling for mold or asbestos (this shop samples neither and refers both to a licensed specialist), and does not cover duct cleaning scope, which has its own SOP. It also does not cover the combustion repair: this procedure detects a spillage condition and stops.

Roles and responsibilities

Procedure

1. Enter with a personal CO monitor already running and read the occupied space first. Clip it at breathing height before the door opens, then read standing in the main living area with nothing running. Acceptance: 0 ppm ambient; any reading above zero in occupied space is a finding, not a rounding error. Hazard in this step: carbon monoxide is odorless and your nose is not an instrument. OSHA's general industry limit of 50 ppm as an 8 hour time weighted average (29 CFR 1910.1000, Table Z-1) runs to you as an employee, not to the homeowner beside you, whose protection is a listed CO alarm and your ordinary duty of care. Stop rule: at a sustained reading in the tens of ppm everyone leaves the building, you call from outside, and the gas utility or fire service is notified.

2. Interview for pattern before you interview for symptom. Ask who is affected, which rooms, what time of day, which season, and whether it stops when they leave for a day. Acceptance: one written sentence naming a person, a room and a time window. What wrong looks like: an answer with no pattern in it ("the air just feels bad"), which usually means odor or humidity rather than a discrete contaminant. Stop rule: if the pattern points at one occupant with symptoms nobody else has, say plainly that a medical question belongs to their physician and that your job is the building. Do this before unpacking instruments; it sets the order of everything after it.

3. Take the outdoor baseline before any indoor number. Standing away from exhaust terminations and the driveway, record outdoor dry bulb, RH and CO2. Acceptance: a written outdoor CO2 figure, typically in the low 400s ppm at ground level away from traffic, plus temperature and RH. Every indoor CO2 number on this visit is read as a rise above this baseline, never as an absolute, and a tech who skips it has no denominator. What wrong looks like: a baseline taken next to a running car or a dryer vent, which inflates it and makes the house look better ventilated than it is. Re-take at a clean location.

4. Measure room by room at breathing height, doors as the occupants keep them. In each complaint room plus one control room, record temperature, RH and CO2 at roughly 4 feet, door in its normal position, system in its normal mode. Acceptance: a value in every cell of the grid with door state and system state beside it. RH has a commonly cited control band of 30 to 60 percent, and here the upper bound is what matters, because sustained RH above about 60 percent supports microbial growth and dust mites. What wrong looks like: readings taken after you have stood in a small closed room, which measures your own exhaled CO2. Re-do standing back.

5. Assess ventilation against the requirement, not against a feeling. Identify what supplies outdoor air: a dedicated fan, a ducted outdoor air connection, an ERV or HRV, or nothing. Acceptance: a required whole-house rate calculated and written next to installed capacity. ASHRAE 62.2, in the edition your jurisdiction has adopted, sets it, and the 2019 edition's whole-house rate is 0.03 cfm per square foot of conditioned floor area plus 7.5 cfm per bedroom plus one. CO2 is a proxy for outdoor air per person, not a toxicant at these levels, and neither 62.1 nor 62.2 sets a CO2 cap; the often-quoted 1,000 ppm figure has an odor and satisfaction basis. What wrong looks like: calling a house under-ventilated from CO2 alone with no installed-capacity figure beside it.

6. Run the worst case depressurization test with the combustion zone monitored, and abort on CO. Close the house, run every exhaust device (range hood, all bath fans, dryer, plus the air handler if returns are in the combustion zone), fire the water heater, and test for spillage at the draft hood with a smoke source while watching your CO monitor in that zone. Acceptance: no spillage after normal establishment time and no CO rise. Hazard created by your own command here: you are deliberately putting the combustion zone under negative pressure, the exact condition that makes an atmospherically vented appliance spill indoors, so occupants and pets stay out of that zone, the test never runs unattended, and you abort and open the zone to outdoor air the moment CO rises. Stop rule: sustained spillage or any CO ends the assessment. Shut the appliance off at its gas valve, tag it, tell the occupant plainly it is not to be used, phone the service manager.

7. Inspect filtration and the distribution it sits in, together. Record the filter's nominal size, MERV rating (ASHRAE 52.2 is the rating method), condition, and whether air bypasses it at the frame, then measure total external static across the air handler against the blower's rated maximum on the nameplate. Acceptance: filter seated with no visible bypass gap and measured static at or below the nameplate rating. What wrong looks like: a high MERV filter already fitted to a system whose static is over the blower's rating, which is airflow starvation that later shows up as a frozen coil. Stop rule: never recommend a filter upgrade off a static reading you have not taken; if the system is already over rated static, the finding is airflow.

8. Walk the moisture path: crawlspace or basement, attic, and any surface the occupant named. Look for bare earth without a vapor retarder, standing water, disconnected return ducts pulling from those spaces, and staining at the ceiling plane. Acceptance: a written condition per space plus a surface temperature reading anywhere condensation was reported. Hazard in this step: a summer attic is a heat exposure and a crawlspace is a confined, poorly ventilated space with unknown air, so carry a light, tell someone you are down there, and come out on your own schedule. What wrong looks like: an open return seam in a vented crawlspace, which outranks every other finding in the report.

9. Present findings in measurement order and name no product until the causes are on the table. Read back the outdoor baseline, the room grid, required versus installed ventilation, the combustion result, the static reading and the moisture conditions, then name causes in the order they matter. Acceptance: the occupant can repeat back what the top finding is. What wrong looks like: leading with a piece of equipment. Stop rule: if a combustion or moisture finding is open, the conversation ends there and nothing is quoted that visit, because selling into an unresolved safety finding is how a shop ends up owning it.

The record this produces

The findings sheet is the deliverable, built from fields captured live: arrival ambient CO; the interview sentence naming person, room and time window; the outdoor baseline row; a room grid with one row per room and columns for temperature, RH, CO2, door state and system state; the required whole-house rate from the 62.2 calculation next to installed capacity; the depressurization result with the devices that were running; total external static against the nameplate rating; filter size, MERV and bypass condition; and moisture conditions per space.

Three people read it later. The tech doing the post-remediation retest, who needs the same rooms at the same door states for the comparison to mean anything. The service manager, deciding whether a proposal is supported. And the shop itself if the complaint becomes a dispute, when a dated grid of readings and a documented stop is worth more than anyone's recollection.

Worked pass: 1998 two-story, three bedrooms, stuffy bedroom complaint

House is 1,900 square feet conditioned, three bedrooms, gas water heater and gas furnace in a utility closet off the kitchen, single return.

Monitor on entering read 0 ppm in the living room. The interview gave a clean pattern: one occupant, master bedroom, worst on waking, door closed overnight, better on vacation. Outdoor baseline at the side yard away from the dryer vent: 71 F, 58 percent RH, 421 ppm CO2. Master bedroom the next morning before the door opened read 1,850 ppm CO2, 74 F, 52 percent RH, a rise of 1,429 ppm above the 421 ppm baseline. That rise is the number that matters, not the 1,850. The control room, an open plan living area, read 690 ppm, a rise of 269 ppm.

Step 5 put a requirement against it. Under ASHRAE 62.2-2019 the whole-house rate is 0.03 times 1,900 square feet, which is 57 cfm, plus 7.5 times four (three bedrooms plus one), which is 30 cfm, for 87 cfm total. Installed continuous outdoor air capacity: none, two intermittent bath fans, no ERV. The CO2 flag and the calculated shortfall agree, which is what you want before writing a ventilation finding.

Step 6 FAILED. Worst case set up with range hood on high, both bath fans running, dryer running, air handler in fan mode, house closed. The water heater fired and spilled at the draft hood continuously, and the personal monitor in the utility closet came off zero and kept climbing through the low tens of ppm over about two minutes. Under this step's stop rule that ended the assessment: exhaust devices off, closet and kitchen opened to outdoor air, water heater shut off at its gas valve and tagged, occupant told plainly not to use it until a gas appliance tech had corrected it, service manager phoned from the driveway. Steps 7 and 8 were not run that day.

That changes the report, not just the schedule. The assessment is genuinely incomplete and the sheet says so rather than presenting a partial visit as finished. The stuffy bedroom is real, and the 1,429 ppm rise and the 87 cfm shortfall are both documented, but they are now the second finding. The first is an atmospherically vented water heater that spills under a house pressure the occupants create every laundry day with the range hood on. Adding ventilation equipment without fixing that appliance would have deepened the depressurization, which is the specific way an IAQ visit sold on symptom injures someone: the fix for the second finding aggravates the first.

The return visit, after the water heater was replaced with a sealed combustion unit, re-ran the depressurization test (no spillage, 0 ppm through the full worst case), then completed steps 7, 8 and 9 and quoted balanced ventilation against the 87 cfm figure already on the sheet.

References

• ASHRAE 62.2, ventilation and acceptable indoor air quality in residential buildings, in the edition your jurisdiction has adopted, for the whole-house rate used in step 5
• ASHRAE 52.2, the test method behind the MERV rating referenced in step 7
• 29 CFR 1910.1000, Table Z-1, for the general industry carbon monoxide permissible exposure limit that applies to you as an employee
• Manufacturer nameplate and installation instructions for the air handler's rated maximum external static pressure
• See related: Callback Within 30 Days Investigation; Equipment Handover Walkthrough With the Customer