Worst case depressurization
Exhaust fans running and the building set up to make draft as difficult as it realistically gets. An appliance that passes only under favorable conditions has not passed.
Indoor Air Quality Testing That Produces Readings, Not a Sales Pitch
Particulate, carbon dioxide, humidity across a full cycle and combustion safety, measured and written up before any equipment is discussed.
- Particulate and carbon dioxide measured
- Humidity logged across full cycles
- Combustion draft tested under load
- Written report before any recommendation
Air quality is the easiest area of this trade to sell equipment into, because nobody can see the problem and nobody can see the improvement.
Air quality is unusual in that the complaint is real, the cause is invisible, and the market is full of appliances that promise to fix it. A household that feels a room is stuffy, or notices dust returning within days of cleaning, or cannot get comfortable at a temperature that used to be fine, is describing something genuine. What they cannot do is identify which of a dozen possible causes is responsible.
That is a poor position from which to buy equipment, and it is exactly the position most air quality purchases are made in. An appliance gets installed, the household is told the air is now better, and there is no measurement at either end to confirm it. Sometimes the appliance addressed the actual problem. Often it addressed a different one, and occasionally, where a dense filter was added to a duct system that could not afford the pressure, it made the overall situation worse.
The alternative is unglamorous: measure first. Particulate concentration establishes whether there is a filtration or infiltration issue. Carbon dioxide relative to outdoors establishes whether the space is adequately ventilated for the number of people in it. Humidity logged across equipment cycles establishes whether the system is actually controlling moisture or only temperature. Combustion safety establishes whether anything dangerous is happening.
Testing has been part of the work in Delta, UT since 2006 and the deliverable is a written report. Where it concludes that nothing needs installing, it says that.
Four measurements that characterize most complaints
Particulate concentration is the one people intuitively expect. It is measured in the fine fraction, which penetrates deep into the respiratory tract and stays airborne for long periods, and the coarser fraction that settles as visible dust. High readings point at filtration, at unfiltered air entering the system, or at an indoor source such as combustion, cooking or activity.
Carbon dioxide is the one people find surprising, and it is arguably the most informative. At residential concentrations it is not itself a health hazard, but because occupants generate it continuously, its level relative to outdoor air tells you how much outdoor air the space is getting per person. A bedroom where it rises steeply overnight is under ventilated, and that deficiency applies equally to every other pollutant produced indoors.
Humidity is measured over time rather than sampled. A single reading says very little; the behavior across a full equipment cycle says a great deal. A cooling system that short cycles will show temperature under control and humidity drifting upward, which is the signature of the clammy house that reads correctly on a thermostat.
Temperature stratification completes the picture. Substantial differences between rooms, or between floor and ceiling in the same room, indicate a distribution problem rather than an air quality one, and it is worth knowing that before buying anything intended to clean the air.
Where unfiltered air gets into the system
A high particulate reading in a home with good filtration usually means air is bypassing the filter. The return side of a duct system is under negative pressure, so any opening in it draws air from whatever space surrounds it. A return running through an attic, a crawl space or a garage with unsealed joints is pulling that air into the distribution system and delivering it to the living space, filtered only by whatever happens to be in the path downstream.
Filter bypass at the rack itself is the other common route. A filter that does not fit its slot snugly, or a rack with an open gap beside the filter, lets air take the easy path around the media rather than through it. It is a small defect with a disproportionate effect.
Both of these are cheap to correct and neither requires new equipment, which is why they get looked for before anything is recommended.
| What the household reports | Likely mechanism | The reading that confirms it |
|---|---|---|
| Dust returns within days of cleaning | Filter bypass or unfiltered air entering the return | Coarse particulate elevated with filtration apparently adequate |
| A bedroom feels stuffy by morning | Insufficient ventilation for the occupancy | Carbon dioxide climbing steeply overnight relative to outdoors |
| Cold but clammy in summer | Short run times removing little moisture | Humidity drifting upward while temperature holds at setpoint |
| Static and dry airways in winter | Low absolute moisture and high air exchange | Relative humidity persistently low across cycles |
| Upstairs hot, downstairs cold | Distribution and stratification, not air quality | Temperature differential between floors and at ceiling level |
| Odor near the furnace or water heater | Poor draft or spillage from a combustion appliance | Draft test at the flue plus carbon monoxide in the space |
The combustion safety element
Every visit includes it, whatever prompted the call, because it is the only measurement on the list where the answer can matter immediately.
Any appliance burning fuel inside a building produces carbon monoxide among its combustion products and relies on its vent to carry them out. Atmospherically vented appliances, meaning those that depend on natural draft rather than a fan, are the vulnerable case. Natural draft is gentle, and a house that is slightly negative relative to outdoors can overcome it, drawing combustion products back down the flue into the room.
Testing therefore happens under worst case conditions rather than ideal ones. Exhaust fans are run, the building is configured to maximize depressurization, and draft is confirmed at the flue with the appliance operating. A vent that drafts perfectly on a still day and spills when the range hood and the bathroom fan are both running is a real hazard that a casual inspection would miss entirely.
Where a problem is found it is reported immediately rather than written into a report for later, and where the situation warrants it the appliance is shut down.
Filter resistance
Pressure drop across the filter compared against the static the blower has available. Better filtration needs more surface area, not denser media in the same slot.
Return side integrity
Joints in the return inspected wherever it crosses unconditioned space, since a negative pressure duct draws in whatever surrounds it.
Humidity over time
Logged across cycles rather than sampled, because the pattern reveals whether the equipment is controlling moisture or only temperature.
Why recommendations follow the readings
Each measured problem has a different remedy and they are not interchangeable. A particulate problem caused by filter bypass is corrected by fixing the rack, which costs very little. The same problem caused by a leaking return in a crawl space is corrected by sealing. Neither is addressed by adding an air cleaner, which would sit downstream of the actual cause.
A ventilation deficiency is not solved by filtration at all, because filtering the same stale air repeatedly does nothing about the carbon dioxide or about anything else accumulating in it. It needs outdoor air introduced deliberately.
A humidity problem in cooling season frequently traces back to equipment sizing and run times rather than to any air quality appliance. Correcting that may mean addressing distribution, or it may mean accepting a dedicated dehumidifier, and the readings indicate which.
That is the whole argument for measuring first. Four plausible complaints, four different remedies, and almost no overlap between them.
A recommendation to install air quality equipment that is not preceded by a measurement should be treated with suspicion, including a recommendation from this company.
Ventilation, and the tightening of buildings
Older housing ventilated itself by accident. Air leaked in around window frames, through the roof space, past the sill plate and up through the floor, and while that wasted an enormous amount of energy it did keep the air exchanging. Nobody had to think about it.
Improving a building envelope removes that accidental ventilation and replaces it with nothing, unless somebody deliberately adds it back. New windows, air sealing work, insulation and a tighter roof all reduce energy use and all reduce air exchange at the same time. This is why a renovation is one of the more common reasons a household starts noticing air quality at all.
The remedy is controlled ventilation rather than deliberate leakage, meaning a known quantity of outdoor air brought in through a path where it can be filtered and, in an energy recovery arrangement, where it can exchange heat with the air leaving. That is a considerably better outcome than random leakage through the shell of the building, but it has to be designed rather than assumed into existence.
Carbon dioxide logging is how the need gets established. A building where it stays close to outdoor levels through an occupied evening is ventilating adequately. One where it climbs steadily is not, and the size of that climb indicates roughly how much outdoor air is missing.
How the assessment runs
Take the complaint properly
What is noticed, in which rooms, at what times of day and in which seasons. The pattern narrows the likely mechanism considerably before any instrument comes out.
Establish an outdoor baseline
Particulate and carbon dioxide measured outside, since indoor readings are only meaningful relative to what is coming in.
Survey the building
Occupancy, combustion appliances, existing ventilation provision, obvious moisture sources and any recent work that changed the envelope.
Deploy the instruments
Logging placed in the affected rooms and at the equipment, capturing humidity and carbon dioxide across full equipment cycles rather than as spot readings.
Measure the system side
Filter resistance against available static, return side integrity where it crosses unconditioned space, and filter fit at the rack.
Combustion safety testing
Draft confirmed at each atmospherically vented appliance under worst case depressurization, plus carbon monoxide in the living space.
Interpret against the complaint
Readings compared with what the household described, so the conclusion explains the actual experience rather than listing numbers.
Report in priority order
Written findings with the remedies ranked by what is worth doing, including the option of doing nothing where that is the honest answer.
- Outdoor baseline taken so indoor readings mean something
- Humidity and carbon dioxide logged over time, not sampled
- Filter resistance checked against the blower's available static
- Combustion draft tested under worst case conditions
- Written report issued before any equipment is proposed
Assessment questions
What testing covers and what it deliberately leaves to specialists
Air quality attracts a lot of loose claims. These answers set out what is measured here and what is not.
Particulate concentration in the fine and coarse fractions, carbon dioxide as an indicator of how well the space is ventilated relative to its occupancy, relative humidity tracked across a full equipment cycle rather than as a single reading, and temperature stratification between rooms and between floor and ceiling.
Alongside those, carbon monoxide is measured in the living space and combustion appliances are checked for correct draft. That last item is a safety measurement rather than a comfort one and it is included regardless of what prompted the visit.
Because it is the most practical proxy for ventilation. People exhale it continuously, so its concentration relative to outdoor levels tells you how much outdoor air the space is actually receiving per occupant.
A room where it climbs steeply through an evening and falls overnight is a room with insufficient ventilation, and that same deficiency applies to every other pollutant generated indoors. It is a single measurement that characterizes the whole air exchange picture.
Mold identification and quantification is a specialist discipline with its own laboratory methods, and it is outside what this testing covers. What the visit does is look for the conditions that allow mold: sustained high relative humidity, cold surfaces where moisture condenses, standing water in a condensate pan, and duct passing through humid unconditioned space.
Where those conditions are found they get reported with the readings. Where there is visible growth or a persistent musty odor, the recommendation is an assessment by someone who does that work specifically, rather than an opinion from this visit.
It affects comfort, health and the building. Air that is too dry produces static, dry airways and shrinkage in wood and joinery. Air that is too humid feels unpleasant at reasonable temperatures, encourages dust mites and mold, and condenses on cold surfaces.
What matters more than a single reading is the behavior across a cycle. A cooling system that satisfies the thermostat quickly never runs long enough to remove much moisture, which produces a house that reads correctly on a thermometer and feels clammy. That pattern is only visible if humidity is logged over time rather than sampled once.
It will tell you what problem exists, which is a different thing and a more useful one. A measured particulate issue points toward filtration and toward finding where unfiltered air is entering the system. A ventilation deficiency points toward outdoor air provision. A humidity problem points toward equipment runtime, sizing or a dedicated appliance.
Selling equipment without that measurement first is how households end up with an expensive appliance addressing a problem they did not have. Where the honest answer is that the readings look reasonable and nothing needs installing, that is what the report says.
Because a filter is a restriction, and a dense filter media fitted into a rack sized for a thin one can absorb a large share of the pressure the blower has available. The consequence is reduced airflow, which reduces capacity, lengthens run times and in cooling can drop the coil below freezing.
The remedy is almost never less filtration. It is more filter area, which means a deeper cabinet so the same quality of media presents a much larger surface to the airstream. Getting this wrong is how a well intentioned air quality improvement degrades the whole system.
Any appliance burning fuel indoors relies on a vent to carry its products out. If that vent does not draft properly, or if the space is depressurized enough to overcome the draft, those products enter the building. Carbon monoxide is the hazard.
The test involves running the appliance and confirming draft at the flue, including under worst case conditions with exhaust fans operating and the building configured to maximize depressurization. It is a short test and it is the most consequential measurement taken during the visit.
The measurement session is typically a couple of hours, because humidity and carbon dioxide behavior only become meaningful when logged across equipment cycles rather than sampled once. Where a pattern needs longer observation, a logger can be left in place and collected afterwards.
The written report follows, setting out what was measured, what the readings indicate, and what would change them, in order of what is actually worth doing.
Not necessarily. The clearest reasons to test are a specific unexplained complaint, a persistent dust or odor problem, a building that feels stuffy or clammy despite the equipment working, or a recent renovation that changed the envelope or the ventilation.
The combustion safety element is worth having regardless, and it is quick. Any home with a fuel burning appliance benefits from knowing that appliance drafts correctly under realistic conditions, which is not something that can be established by looking at it.
What testing usually points toward
The remedies sit across filtration, distribution and leakage rather than in a single product.
Measure before buying anything that claims to clean the air
Four common complaints have four different causes and four unrelated remedies. A couple of hours of measurement is what tells you which one you actually have.
Assessments across Delta, UT, with the combustion safety element included regardless of what prompted the visit.