Indoor Air Quality Guide for North Texas Homes

Indoor air quality is not one problem with one product solution. It is a set of separate issues — particles, moisture, ventilation, gases and combustion byproducts — that come from different sources, are measured with different instruments, and are corrected in different ways. A filter upgrade addresses one of them.

This guide walks through each category, what can reasonably be measured in a home, and where measurement stops and professional laboratory or medical evaluation begins.

Scope note: HVAC testing and consumer-grade indoor air quality screening are useful for finding airflow, ventilation, humidity and equipment problems. They are not a medical evaluation and not a laboratory analysis. Nothing here diagnoses a health condition. If a carbon-monoxide alarm sounds or anyone has headache, dizziness, nausea, confusion, weakness, chest pain or difficulty breathing, move everyone into fresh air and call 911 or the fire department.

Particles: Dust, Pollen, Smoke and PM2.5

Particulate matter is the category most homeowners already associate with air quality, and the one filtration genuinely addresses. Sources include outdoor pollen and dust drawn in through the envelope and ventilation, cooking, combustion, candles, wildfire smoke episodes, resuspended house dust, and duct or filter bypass that lets unfiltered air into the air handler.

Particles are described by size. PM2.5 refers to particles 2.5 micrometers and smaller, which stay airborne longer and penetrate deeper into the respiratory tract. EPA's Guide to Air Cleaners in the Home explains the categories of particle air cleaners, what filter ratings mean, and the limits of each approach.

What matters in a real house:

• Filter efficiency has to be matched to the system. A higher-MERV filter with more pressure drop than the blower and duct system can tolerate reduces airflow, which affects capacity, dehumidification and comfort. See Why DFW Homes Have High Static Pressure.
• Bypass defeats efficiency. Gaps around a filter, a leaky return or an unsealed filter rack let air around the media instead of through it.
• Runtime matters. A filter only cleans air the blower moves through it, so short runtimes limit total filtration regardless of rating.
• Portable cleaners are room-scale. A correctly sized portable HEPA unit cleans the room it is in; it does not treat the house.

Moisture and Humidity

Moisture is the category with the widest set of consequences: comfort, material damage, condensation and microbial growth potential all track it. Sources include outdoor humidity infiltrating the envelope and ducts, occupant activity, unvented combustion, plumbing leaks, ground moisture and duct or equipment condensation.

Indoor relative humidity is straightforward to measure with an inexpensive hygrometer, and worth logging in more than one room. Persistent condensation on windows or supply registers, musty odor, or damp materials are signs to investigate the moisture source rather than to buy an air cleaner. Extremely dry conditions cause their own comfort and material problems.

Where HVAC is involved, humidity is usually a runtime, airflow and capacity question: oversized equipment that satisfies the thermostat quickly removes less moisture, and airflow that is too high across the coil reduces latent capacity. Duct leakage in a hot, humid attic can also import moisture directly.

Ventilation and Carbon Dioxide

Ventilation is the deliberate exchange of indoor air with outdoor air. Older leaky homes did much of this accidentally; tighter homes do not, and many houses have no continuous ventilation system.

Indoor CO2 is commonly used as an indicator of outdoor-air supply relative to occupancy, because occupants are the dominant indoor source. It is not a general index of air quality and not a toxicity reading at residential levels. The ASHRAE Position Document on Indoor Carbon Dioxide covers both the legitimate use and the common misreadings, and the U.S. Department of Energy's measured ventilation and IAQ data from recently constructed homes shows how much delivered ventilation varies from design intent in practice. Residential ventilation rates themselves are addressed in ASHRAE Standard 62.2.

Adding ventilation is not free of consequences: outdoor air brings its own temperature, humidity, particles and pollen, and exhaust-only strategies depressurize the house, which interacts with atmospheric-vented combustion appliances. Full detail is in Home Office CO2 and Ventilation in North Texas.

VOCs and Formaldehyde

Volatile organic compounds are a large family of carbon-based chemicals that evaporate at room temperature. They come from building materials, furnishings, adhesives, paints and finishes, cleaning and personal-care products, fuels, hobby materials and attached garages. EPA's overview of volatile organic compounds' impact on indoor air quality and its page on formaldehyde's impact on indoor air quality are the practical starting points, including source-control guidance.

Two points are essential and often misstated:

• "TVOC" is a screening number, not a health metric. A photoionization detector (PID) or similar total-VOC sensor responds to a mixture of ionizable compounds. It can show that levels changed — higher in one room, higher after a renovation, lower after ventilation — but it generally cannot identify which compounds are present. Different VOCs have very different toxicity and very different exposure guidance, so a single total number cannot be converted into a health conclusion. There is no one universal residential TVOC health threshold.
• Odor does not identify a chemical. A "new" smell does not establish that formaldehyde, benzene or any other specific compound is present, and the absence of odor does not establish that nothing is.

When a specific chemical is suspected — because of a known material, a documented exposure or a physician's question — the appropriate step is targeted sampling and laboratory analysis using a method suited to that compound, arranged through a qualified professional such as an industrial hygienist or an accredited environmental laboratory. New-construction detail is in Off-Gassing and VOCs in New North Texas Homes.

Carbon Monoxide and Combustion Byproducts

Fuel-burning appliances — furnaces, water heaters, ranges, dryers, fireplaces and space heaters — produce combustion products. When combustion and venting are working as designed, those products leave the building. When they are not, carbon monoxide and other byproducts can enter occupied space.

This is the one IAQ category that is a life-safety issue rather than a comfort issue, and it is handled with listed CO alarms, correct venting, adequate combustion air, and appliance testing by a qualified technician against the manufacturer's specifications. CDC's carbon monoxide information covers sources, symptoms and what to do. Two dedicated guides go further: Incomplete Combustion in Homes and Low-Level Carbon Monoxide in Homes.

Gas cooking deserves its own mention: a range hood that exhausts outdoors, used while cooking, is the primary control. A recirculating hood does not remove combustion products from the house.

Source Control First

Across EPA guidance, the consistent order of operations is source control, then ventilation, then air cleaning. Source control is unglamorous and effective:

• Remove, replace, seal or relocate the material or product that is emitting.
• Vent the activity that generates pollutants — cooking, bathing, hobbies — directly outdoors while it happens.
• Repair the moisture problem instead of managing its symptoms.
• Keep vehicles and fuel-powered equipment out of attached garages, and air-seal the garage-to-house boundary.
• Fix duct leakage and filter bypass so the system stops importing attic and wall-cavity air.

Filtration and Air Cleaning: What Each Method Can Do

Approach	What it can address	What it cannot address	Key limitation
Particle filtration (media filter, MERV-rated)	Airborne particles, including a portion of PM2.5 depending on rating	Gases, vapors, carbon monoxide, carbon dioxide	Pressure drop must be within the system's airflow capability; bypass defeats it
Portable HEPA cleaner	Particles in the room it serves	Gases; other rooms	Room-scale only; sizing and runtime determine effect
Activated carbon or other sorbent media	Some gases and odors, depending on the compound	Particles; carbon dioxide	Depends on media quantity, contact time, airflow, gas type and replacement condition; thin carbon-coated filters hold little media
Outdoor-air ventilation (exhaust, supply, ERV/HRV)	Dilution of occupant-generated CO2 and many indoor-source gases	Outdoor pollutants entering with the air	Adds heating, cooling and humidity load; needs filtration and pressure consideration
Local exhaust (range hood, bath fan)	Pollutants and moisture at the point of generation	Whole-house pollutant sources	Must exhaust outdoors and actually be used
UV and other additive devices	Claims vary widely by device and are highly product-specific	Should not be assumed to address particles or gases	Verify third-party testing for the specific product and check byproduct data, including ozone

EPA's Guide to Air Cleaners in the Home is the reference to read before buying anything in this table.

Testing Limitations

What field measurement is good for: finding low airflow, high static pressure, duct leakage, humidity problems, missing or inadequate ventilation, and combustion appliance faults. Those are the mechanical causes behind most of what homeowners describe as an air-quality complaint, and they are measurable.

What field screening cannot do:

• Identify individual chemical compounds from a total-VOC reading.
• Establish a health risk or exposure conclusion from a screening number.
• Rule out a specific contaminant that was not measured.
• Substitute for a physician's evaluation of symptoms, an industrial hygienist's exposure assessment, or an accredited laboratory's analysis.

Our $89 Comfort Audit is an HVAC and building performance evaluation: airflow, static pressure, duct condition, humidity, ventilation and combustion safety checks on gas appliances. It is not a medical assessment and not a laboratory IAQ analysis, and it is not represented as one. Where the findings point to filtration, ventilation or equipment work, our Indoor Air Quality and Indoor Air Management System services handle it; where they point outside our scope, we say so.

Where to Read Next

• Home Comfort and Indoor Air Quality Guides — the full Home Comfort hub.
• Home Office CO2 and Ventilation
• Off-Gassing and VOCs in New North Texas Homes
• Incomplete Combustion in Homes
• Low-Level Carbon Monoxide in Homes

Frequently Asked Questions

Will a better filter fix my indoor air quality?

A better filter addresses airborne particles, and only to the extent the system can move air through it without losing airflow. Filters do not remove gases such as carbon dioxide or the vapors from building materials and products, and they do nothing about moisture or a combustion venting fault. Substantial activated-carbon media can reduce some gases, depending on the compound and the amount of media, but that is a different product from a pleated particle filter.

Do particle filters remove VOCs or carbon monoxide?

No. Particle media captures particles; gases pass through. Sorbent media such as activated carbon can adsorb some gases, with effectiveness depending on the gas, the quantity of media, airflow and contact time, and how recently the media was replaced. Carbon monoxide is not controlled by air cleaning at all — it is controlled by correcting the combustion or venting problem and by listed CO alarms.

What does a TVOC reading actually tell me?

It tells you that the total concentration of ionizable volatile compounds the sensor responds to is higher or lower than another reading you took. That makes it useful for comparisons: room to room, before and after ventilating, or over time in a new house. It does not identify individual compounds and it cannot be converted into a health conclusion, because different VOCs have very different toxicity and guidance.

Is there a safe TVOC number for a home?

There is no single universal residential TVOC health threshold. Guidance addresses individual compounds, each with its own exposure considerations, which is why a total number cannot stand in for them. If a specific chemical is a concern, targeted sampling and laboratory analysis arranged through a qualified professional is the appropriate step.

Does duct cleaning improve air quality?

It can help when ducts are visibly contaminated, after construction work, or where there is confirmed debris or moisture, and it does nothing for gases, carbon dioxide or humidity. In most homes the larger measurable gains come from sealing duct leakage and filter bypass, correcting airflow and static pressure, and providing ventilation and local exhaust — because those change what enters the airstream in the first place.

Does the Comfort Audit tell me if my air is making me sick?

No, and we will not claim otherwise. The Comfort Audit measures HVAC and building performance — airflow, static pressure, duct condition, humidity, ventilation and combustion safety on gas appliances — and identifies mechanical problems that affect comfort and air quality. Health questions belong with a physician, exposure assessments with an industrial hygienist, and specific chemical analysis with an accredited laboratory.