Can too much air sealing cause indoor air quality problems in NB homes? | Insulation IQ?

Yes, and this is one of the most important questions any New Brunswick homeowner can ask before starting a serious air sealing project. The short answer is: a very tightly sealed home without a deliberate mechanical ventilation strategy can absolutely develop indoor air quality problems. This is not a reason to avoid air sealing — it is a reason to air seal properly and plan for ventilation at the same time.

The concept is captured in the building science phrase "build tight, ventilate right." In older NB homes, particularly the leaky post-war bungalows common in Fredericton's north end or the drafty century homes in Saint John's south end, the building envelope was so porous that fresh outdoor air was constantly infiltrating through walls, floors, and attic bypasses. This uncontrolled air movement was miserable — it caused cold drafts, ice damming, sky-high NB Power bills — but it did incidentally dilute indoor pollutants. When you seal all those pathways without adding controlled ventilation, you can trap moisture, volatile organic compounds (VOCs), combustion byproducts, radon, and carbon dioxide inside the living space.

Moisture is the most immediate concern in New Brunswick's climate. Climate zone 6 means cold winters with interior humidity from cooking, bathing, and breathing. In a leaky house, that moisture escaped. In a tight house, it accumulates — leading to condensation on cold surfaces, elevated relative humidity, and eventually mould growth, which is a serious health hazard. The NB Building Code and ASHRAE 62.2 both recognize that controlled ventilation is required once a house reaches a certain level of air tightness.

Radon is the second major concern specific to New Brunswick. Parts of the province, particularly areas underlain by granite bedrock common around Fredericton and portions of the Saint John River valley, have elevated radon potential. Health Canada's residential guideline is 200 Bq/m³. A tight house without sub-slab depressurization can concentrate radon to dangerous levels. If you are air sealing a basement in these areas, radon testing before and after is strongly advised.

Combustion appliances present another risk. Natural gas furnaces, oil boilers, wood stoves, and fireplaces all need combustion air. In a very tight house, a drafty old oil furnace may backdraft — pulling flue gases, including carbon monoxide, back into the living space instead of exhausting them. This is a life-safety issue. Any serious air sealing project should include an assessment of all combustion appliances and, where needed, ensure they are either direct-vented (sealed combustion) or that dedicated combustion air intakes are provided.

The practical solution for most NB homeowners is to pair aggressive air sealing with a Heat Recovery Ventilator (HRV). An HRV continuously supplies fresh outdoor air and exhausts stale indoor air, recovering 70–80% of the heat energy in the process. This maintains excellent indoor air quality without the energy penalty of simply opening a window all winter. HRV installation typically costs $1,500–$3,000 in New Brunswick, and the equipment itself qualifies under NB Power's Home Energy Savings Program and may contribute to Canada Greener Homes Grant eligibility.

The NB Building Code (adopting NBC 2015 with provincial amendments) requires mechanical ventilation in new construction once air tightness targets are established. For older homes undergoing deep energy retrofits, the same logic applies even if it is not always explicitly enforced. A blower door test — which pressurizes the house to measure air changes per hour at 50 pascals (ACH50) — tells you exactly how tight your home is and guides how urgently an HRV is needed. Most energy auditors working in Moncton, Fredericton, and Saint John offer blower door testing as part of an EnerGuide evaluation.

In summary: excessive air sealing without mechanical ventilation can degrade indoor air quality, but the solution is not to leave gaps in your building envelope. It is to seal deliberately, test with a blower door, install an HRV, and test for radon. Done correctly, a tight, well-ventilated New Brunswick home will have far better air quality than the draughty, pollutant-harbouring alternative.

If you are planning a whole-home air sealing project in New Brunswick, connecting with an experienced local insulation contractor through New Brunswick Insulation or the New Brunswick Construction Network can help you find professionals who understand the climate zone 6 requirements and will design the ventilation strategy alongside the sealing work.

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Looking for experienced contractors? The New Brunswick Construction Network connects homeowners with qualified professionals:

• Arctic Fox Construction Inc.
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• 3Tone Construction Ltd
• Brunswick insulation & roofing
• Gionetterenovations