The same energy efficiency movement that is rightly pushing builders to seal homes against air infiltration has created a hidden crisis: we sealed out the drafts, but we didn't replace them with intentional, controlled, filtered fresh air. The result is the most energy-efficient and the most chemically concentrated indoor air environment in the history of residential construction.
The Problem With Tight Homes
For most of the 20th century, American homes leaked. Gaps around windows, doors, electrical outlets, and plumbing penetrations allowed a continuous, uncontrolled exchange of indoor and outdoor air. It was inefficient — heating and cooling dollars drifted out through every crack. But it also diluted indoor pollutants, flushed moisture, and prevented CO₂ accumulation. The leaky house was breathing, even if it didn't know it.
Beginning with the energy crises of the 1970s and accelerating through successive iterations of energy codes, builders began sealing those gaps. Today, a code-compliant new home in most jurisdictions is dramatically tighter than anything built before 2000. This is genuinely good for energy performance. The reduction in heating and cooling loads is real, measurable, and significant.
The problem is that we sealed the house without replacing what those drafts were doing. A tight home without mechanical ventilation doesn't just save energy — it concentrates everything the occupants emit, exhale, cook, clean with, and live among.
The EPA's finding: Indoor air in American homes is typically 2 to 5 times more polluted than outdoor air, and in some cases more than 100 times worse. The primary driver is not outdoor pollution entering — it is indoor pollution accumulating without adequate dilution.
Every building material off-gasses. Every human exhales CO₂ and water vapor. Every cooking event releases particulate matter, nitrogen dioxide, and volatile organic compounds. Every cleaning product introduces chemical vapors. In a leaky home, these disperse. In a tight home without ventilation, they accumulate — and peak concentrations can reach levels that would trigger air quality alerts outdoors.
We sealed the house. We did not replace what the drafts were doing. The tight home without ventilation is not an energy achievement — it is a concentration chamber.
What Accumulates — and What It Does
The indoor pollutant load in a modern tight home falls into several categories. Understanding each one clarifies why generic air quality interventions — opening windows occasionally, running a portable air purifier — are inadequate responses to a systemic problem.
| Pollutant | Primary Source in Homes | Health Concern | Standard Construction Risk Level |
|---|---|---|---|
| Formaldehyde | OSB, particle board, MDF, engineered wood products | Group 1 carcinogen (IARC); respiratory sensitizer; mucosal irritant | HIGH |
| Total VOCs (tVOC) | Paints, adhesives, flooring, spray foam, cleaning products | Eye/throat irritation; headaches; liver and kidney stress; some carcinogenic | HIGH |
| CO₂ | Occupant respiration; combustion appliances | Cognitive impairment begins at 1,000 ppm; significant at 2,000+ ppm — common in bedrooms | HIGH |
| Moisture / Relative Humidity | Cooking, bathing, respiration, slab off-gassing | Above 60% RH enables mold growth; dust mite proliferation; structural damage | HIGH |
| Particulate Matter (PM2.5) | Cooking (especially gas), candles, dust resuspension | Lung and cardiovascular disease; linked to cognitive decline at chronic exposure | MODERATE |
| Nitrogen Dioxide (NO₂) | Gas cooking, gas furnaces | Respiratory inflammation; asthma trigger; children particularly vulnerable | MODERATE |
| Radon | Soil gas infiltration through slab and foundation | Second leading cause of lung cancer in the US — EPA | SITE-DEPENDENT |
| Isocyanates (MDI/TDI) | Spray polyurethane foam insulation | Potent respiratory sensitizer; can cause permanent occupational asthma | HIGH (if foam present) |
Several of these pollutants interact and compound one another. Elevated CO₂ suppresses the body's ability to detect other irritants. Elevated humidity increases off-gassing rates from formaldehyde-containing materials. VOC concentrations peak in warm conditions — which is to say, exactly when windows are most likely closed and air conditioning is running.
The CO₂ Sleeping Problem
Carbon dioxide deserves particular attention because its indoor accumulation is so poorly understood by the public. Outdoor CO₂ concentration is approximately 420 parts per million (ppm). Most bedrooms in tight homes with two occupants sleeping will rise to 1,500–2,500 ppm over an eight-hour night with no ventilation — levels that peer-reviewed research associates with measurably impaired cognitive function, reduced decision-making quality, and disrupted sleep architecture.
Sleeping in a sealed bedroom is not rest in fresh air. It is eight hours of CO₂ accumulation in the room where the body's repair processes are most dependent on adequate oxygen delivery.
ASHRAE 62.2: The Standard Nobody Follows
There is a published standard for residential ventilation. ASHRAE 62.2, Ventilation and Acceptable Indoor Air Quality in Residential Buildings, specifies minimum mechanical ventilation rates for new construction and existing homes. It has been updated regularly since 2003 and is referenced in the International Residential Code.
In practice, it is widely ignored. Spot ventilation — bathroom exhaust fans, kitchen range hoods — satisfies the code letter in many jurisdictions without addressing the whole-house fresh air requirement. The standard's whole-house ventilation provisions require either continuous exhaust, continuous supply, or a balanced system. The vast majority of Standard-grade homes deliver none of these.
The formula behind ASHRAE 62.2 is straightforward: 0.01 × conditioned floor area (sq ft) + 7.5 × (number of bedrooms + 1). The result is a whole-house mechanical ventilation rate in cubic feet per minute. This airflow must be continuous, or run on a schedule that delivers equivalent total air exchange over 24 hours.
What "0.35 ACH" means in practice: ASHRAE 62.2 also references a minimum of 0.35 air changes per hour (ACH), meaning the entire volume of air in the home should be replaced approximately once every three hours. A 2,000 sq ft home with 9-foot ceilings contains 18,000 cubic feet — requiring roughly 105 CFM continuous ventilation to achieve 0.35 ACH. Most bathroom exhaust fans run only when someone is in the bathroom. They satisfy neither the continuous requirement nor the volume requirement.
ERV vs. HRV: The Domus Ventilation Standard
Whole-house mechanical ventilation means a system that continuously draws fresh outdoor air into the home and exhausts stale indoor air — while recovering the energy embedded in the air being exhausted. Two technologies accomplish this: Energy Recovery Ventilators (ERVs) and Heat Recovery Ventilators (HRVs).
Both systems use a heat exchange core to transfer thermal energy between the incoming and outgoing airstreams, recovering 70–85% of the energy that would otherwise be wasted. This is what allows continuous fresh air ventilation without the energy penalty of simply opening a window — the outgoing air warms (or cools) the incoming air before it enters the living space.
Efficiency — What the Numbers Mean
Both ERV and HRV systems are rated by sensible heat recovery efficiency — the percentage of thermal energy transferred from the outgoing air to the incoming air. High-quality residential units achieve 80–85% efficiency. This means that on a winter day when indoor air is 70°F and outdoor air is 20°F, the incoming fresh air enters at approximately 60–62°F rather than 20°F — dramatically reducing the heating load required to condition it.
0.01 × 2,400 = 24 CFM (area component)
7.5 × (3 + 1) = 30 CFM (occupancy component)
Minimum: 54 CFM continuous — or equivalent intermittent schedule
Integration: Dedicated vs. Ducted Systems
ERV/HRV systems can be installed as standalone units with their own dedicated supply and exhaust ductwork, or integrated with the home's existing forced-air HVAC distribution system. Both approaches are used in Domus-grade construction; the right choice depends on the home's layout, existing ductwork, and the installer's preference.
Standalone systems give more precise control over fresh air distribution — ducts can be targeted to bedrooms, which have the highest CO₂ accumulation concern. Integrated systems reduce installation complexity and cost but require that the air handler run whenever ventilation operates, adding fan energy consumption.
Key performance note: Duct sealing quality directly determines whether the ventilation system works as designed. An ERV or HRV connected to leaky ductwork can achieve 40–60% of its rated performance. All Domus-grade ventilation installations require duct leakage testing to verify delivery — not just airflow measurement at the unit itself.
Standard Construction vs. Domus Ventilation Strategy
Standard Standard-grade construction approaches ventilation as a code compliance exercise. The minimum required to pass inspection. The result is a pattern of spot ventilation — bathroom fans that may or may not run long enough, range hoods venting to the attic instead of outdoors, no whole-house fresh air delivery at all.
The Domus ventilation strategy is built on one principle: make the fresh air intentional, measurable, and controllable. Relying on infiltration — accidental air exchange through gaps — is not a ventilation strategy. It is an undefined and uncontrollable exposure pattern that varies with wind speed, stack effect, and temperature differential in ways no occupant can monitor or adjust.
The Material Connection: Why Ventilation Alone Is Insufficient
Mechanical ventilation is the delivery mechanism for fresh air. It is necessary but not sufficient. A well-designed ERV system continuously dilutes indoor pollutants — but if the source emission rate is high enough, dilution cannot keep up with production.
This is the fundamental limitation of ventilation as a sole strategy: it addresses the symptom (accumulated pollutants) rather than the source (materials that emit them). The Domus approach requires both: eliminate the major emission sources through material selection, then design a ventilation system sized to manage what remains.
The formaldehyde problem: OSB sheathing, particle board, and MDF emit formaldehyde continuously for years after installation. In a 2,000 sq ft home built with standard construction materials, achieving the WHO guideline of 0.08 mg/m³ for formaldehyde would require ventilation rates far above ASHRAE 62.2 minimums — and the material continues off-gassing regardless. The only durable solution is substitution: inorganic materials that do not contain formaldehyde-based resins.
The sequence matters. A home built with mineral wool insulation, MgO sheathing, glass-mat gypsum board, lime plaster walls, and porcelain tile floors has a baseline formaldehyde emission rate near zero. Its ERV needs to manage CO₂, cooking byproducts, and moisture — not fight against the building materials themselves. A Standard-grade home's ERV is fighting a continuous chemical source load on top of the occupant load.
This is why the Salus Standard treats ventilation design as inseparable from material selection. The two are a system. Material chemistry determines the baseline emission load the ventilation must overcome. Ventilation design determines whether that load ever reaches occupant-level concentrations.
The Domus Ventilation Specification
A Salus-compliant ventilation system is not defined by a single product. It is defined by outcomes: continuous, measurable fresh air delivery that meets or exceeds ASHRAE 62.2, with energy recovery, in a system that can be verified, monitored, and serviced. The following checklist captures the key specification requirements.
Recommended manufacturers (residential ERV/HRV): Zehnder ComfoAir (premium balanced, Europe-engineered), Broan-NuTone (widely available, serviceable), Lifebreath (North American, cold-climate HRV specialist), Fantech (commercial-grade options for larger homes), Panasonic WhisperComfort (compact ERV for smaller applications and retrofits). All must be sized per ASHRAE 62.2, not by manufacturer's square footage rule-of-thumb.
Existing Homes: The Retrofit Path
The question most often asked is not about new construction. It's about the home someone already lives in. The good news is that meaningful IAQ improvement is achievable without a full renovation — but it requires an honest assessment of what the existing home is doing and what it is not.
The retrofit ventilation sequence follows a clear priority order:
Step 1: Measure first. Before any intervention, establish a baseline. A CO₂ monitor in the bedroom over several nights and a tVOC monitor in the main living area provide the essential diagnostic data. If bedroom CO₂ consistently exceeds 1,200 ppm or tVOC levels are elevated, the ventilation problem is confirmed. Monitoring costs $100–$250 per device and is the highest-information-density investment available in residential IAQ.
Step 2: Upgrade exhaust ventilation. Replace bathroom fans with properly sized units on automatic timers or humidistat controls. Verify the range hood is ducted to exterior and not recirculating. These are often $200–$600 improvements that address moisture and cooking pollutants at source.
Step 3: Install whole-house fresh air supply. For existing forced-air HVAC systems, the simplest approach is an outdoor air damper system that introduces fresh air into the return plenum — systems like the Broan AI series or equivalent. More comprehensive solutions involve a full ERV or HRV unit connected to dedicated ductwork or to the existing HVAC system. Retrofit ERV installation typically costs $1,500–$4,000 depending on complexity.
Step 4: Address source emissions. In existing homes with high formaldehyde or VOC readings, source remediation is the only durable solution. Low-VOC coating systems (Zinsser BIN for sealing, then mineral silicate or zero-VOC topcoat) can significantly reduce off-gassing from particle board and OSB substrates by encapsulating — though not eliminating — the emission source. Replacing the most egregious materials during planned renovations eliminates the source entirely.
The single most accurate description of a modern Standard-grade home's air quality is this: it is the result of no design decision at all. Ventilation was added to satisfy a code minimum. Materials were selected without regard to their emission chemistry. The occupants arrived to breathe the cumulative output of every shortcut taken in the building process.
The Domus approach is simply the application of intentionality — choosing materials that don't emit what we don't want to breathe, and designing ventilation that continuously replaces what accumulates regardless. These are not exotic interventions. ERVs are standard equipment in European residential construction. ASHRAE 62.2 has existed for two decades. The knowledge exists. The industry simply hasn't been required to apply it.
Build tight, ventilate right. It is not a slogan. It is the minimum viable framework for a home that does not slowly harm the people living in it.