Indoor Air Quality Ontario 2026: HEPA, UV, HRV/ERV, and Radon: What Actually Works

Why Ontario indoor air matters (winter sealing + wildfire smoke)

Ontarians spend roughly 90 percent of their time indoors, and in winter that number pushes even higher. The indoor air you breathe for five to six months a year is a closed loop: your furnace recirculates it, your body adds CO2 to it, cooking and cleaning add volatile organic compounds, and any soil gas (notably radon) entering through the basement slab has nowhere to go. Modern Ontario homes are built or retrofitted to be air-tight for energy efficiency, which is good for your heating bill and a problem for your indoor air if you do not compensate with mechanical ventilation.[2]

The last few summers have added a second pressure: wildfire smoke. Southern Ontario now sees multi-day PM2.5 spikes most summers, and the Air Quality Ontario network routinely publishes elevated fine particle readings across the province during smoke events.[7] Keeping windows closed and running filtered recirculation through a MERV 13 capable system is the standard public health advice during those events, which means the filter you have on your furnace in August matters as much as the one you have in January.

This guide works through the real options in priority order: source control and ventilation first, filtration second, and the marketing-heavy add-ons (UV-C, PCO, ionizers, ozone) last, because that is the order that produces the best actual air quality per dollar spent.

HEPA filtration: what it costs and what it does

HEPA is a defined standard: a filter must capture 99.97 percent of particles at 0.3 microns to earn the label. It is genuinely effective at removing fine dust, pollen, mould spores, pet dander, bacteria, and smoke particles. Where it gets oversold is in how it is installed.[3]

Portable HEPA units (what most Ontario homes actually need)

A single-room portable HEPA purifier costs $100 to $300 for a basic unit and $400 to $800 for a higher-capacity model that can clear a large living room or open-concept main floor. Replacement filters run $30 to $150 per unit and typically need changing every 6 to 12 months. Two well-placed portables (bedroom plus main living area) cover the rooms where you actually spend your waking and sleeping hours, for under $1,000 in equipment.[2]

Whole-home HEPA systems

Installed whole-home HEPA systems run $1,700 to $5,000 or more. The catch is that true HEPA media creates too much static pressure for a typical residential furnace blower. These systems almost always involve a bypass or dedicated booster fan, and most homes that install them could have spent less money and gotten comparable real-world air quality from two portable units plus a better furnace filter.[3]

Furnace filters: the MERV 11 to 13 sweet spot

A standard residential furnace filter is rated on the MERV scale (1 to 16). A basic fibreglass filter is MERV 1 to 4. A pleated filter at MERV 8 is the bare minimum for a modern system. MERV 11 captures fine dust and pollen. MERV 13 captures smoke particles, some bacteria, and most virus-carrying droplets, and is the filter ASHRAE recommends for wildfire smoke events.[5]

Expect to pay $20 to $50 per filter at MERV 8 to 11, and $40 to $100 per filter at MERV 13. Change every three months during heavy use. The practical upper limit for most Ontario furnaces is MERV 13; jumping to true HEPA without blower modifications is how you starve a system of airflow and shorten its life.

UV-C lamps and PCO: what Health Canada and EPA actually say

This is the section where an honest guide has to push back on the sales pitch. In-duct UV-C lamps and photocatalytic oxidation (PCO) devices are sold as germ-killing, VOC-destroying miracle add-ons. An installed in-duct UV lamp typically runs $750 to $2,000.[3]

The EPA's technical summary on residential air cleaners is direct: for in-duct UV-C installed in typical residential systems, there is no proven consumer health benefit under the conditions present in a home. Air moves past the lamp too quickly to deliver a meaningful ultraviolet dose, and the lamp only treats air that passes through the ductwork, not air in the occupied rooms where people actually breathe.[3]

PCO devices (marketed as breaking down VOCs with a titanium dioxide catalyst and UV light) have an additional problem: they can generate ozone and other byproducts as intermediates. The EPA's position on ozone generators marketed as air cleaners is explicit, that they are not safe to use in occupied spaces at concentrations that affect indoor air quality. Ionizers and plasma devices fall into the same category: not recommended without independent evidence for the specific product.[4]

UV-C does have legitimate uses. Upper-room UV-C fixtures in hospital and congregate-care settings, and UV-C on HVAC evaporator coils to prevent biological growth, are both supported by the evidence. Those are not what most Ontario contractors are pitching when they upsell a UV lamp during a furnace install.

If a contractor tells you a UV-C lamp or PCO unit will solve your allergies, asthma, or virus concerns, ask for the specific peer- reviewed evidence for the exact product they are quoting. In most cases the evidence will not materialize and the money is better spent on better filtration and better ventilation.

HRV vs ERV: fresh-air strategy that works

Mechanical ventilation is the part of indoor air quality that actually earns its money in Ontario. A Heat Recovery Ventilator (HRV) or Energy Recovery Ventilator (ERV) continuously exchanges stale indoor air for fresh outdoor air, recovering 70 to 85 percent of the heat in the air you exhaust. You get fresh air without throwing away the heat you paid for.[10]

The Ontario Building Code has required mechanical ventilation meeting CSA F326 in new residential construction since 2012, which in practice means new Ontario homes already have an HRV or ERV.[5] Older homes typically do not, and adding one is the single biggest indoor air quality upgrade a retrofit can buy.

For most Ontario climates (ASHRAE zones 5A and 6A), an HRV is the better choice. Ontario winters are long and dry, and cooking, bathing, and breathing generate indoor moisture that needs to leave the house. An HRV exhausts that moisture with the stale air. An ERV recovers some of that moisture and puts it back, which helps in very dry homes but can contribute to window condensation in normal ones.[5]

A typical HRV installation in Ontario runs $2,500 to $5,000 installed, with the unit alone costing $800 to $2,500. ERV installations run $3,000 to $6,000. Both cost roughly $50 to $100 per year to operate in electricity and another $50 to $100 in filter and core maintenance.[10]

Full comparison of the two systems, including installation options, costs, and maintenance, is covered in our HRV vs ERV Ontario guide.

Radon: the silent Ontario problem

If you only act on one thing in this guide, it should be this one. Radon is a radioactive gas that seeps into homes from soil under the foundation. It is colourless, odourless, and the second leading cause of lung cancer in Canada after smoking. Health Canada estimates 850 Ontario lung cancer deaths per year are radon-attributable.[1]

Health Canada's action level is 200 Bq/m3. Above that number, mitigation is recommended. Below it, no action is needed. Roughly 7 percent of Canadian homes test above the action level, and the distribution is not uniform: some neighbourhoods in Ontario sit on uranium-bearing bedrock and have much higher rates. You cannot guess whether your home has radon by looking at it. You have to test.[1]

A long-term radon test kit costs $30 to $70 and runs for at least 91 days, ideally through a full heating season when your home is closed up. Short-term kits exist but are less reliable and should only be used for screening. Professional radon testing costs $150 to $800 depending on the scope.

If your home tests above 200 Bq/m3, the standard mitigation is sub-slab depressurization: a fan pulls air from under the basement slab and vents it outside, preventing radon from being drawn into the home. Installed cost is typically $2,000 to $3,500 in Ontario, though low-complexity installations can come in closer to $1,500 and complicated homes can run $4,000 or more. The system uses a small fan that costs roughly $50 per year in electricity.[1]

HRVs provide some radon benefit (25 to 50 percent reduction in most homes) because they dilute indoor air, but they are not a substitute for a dedicated mitigation system if your test result is high.[1]

CO and smoke detectors: code and layering

Ontario's Fire Code requires working smoke alarms on every storey of the home and outside all sleeping areas. Carbon monoxide alarms are required outside every sleeping area in homes with fuel-burning appliances, fireplaces, or attached garages.[6]

As of January 1, 2026, the Fire Code was amended to expand CO alarm requirements. The new rules extend coverage to additional building types and add requirements for common areas heated by fuel-burning appliances outside the dwelling unit. Any Ontario homeowner, landlord, or condo board should verify their alarm layout against the new requirements.[6]

Hardwired, battery-operated, and plug-in CO alarms are all permitted. Combined smoke/CO units are common and cost $40 to $100 each. Replace CO alarms every 7 to 10 years depending on the manufacturer, and replace smoke alarms every 10 years.

Full details on the January 2026 code changes, including placement requirements and condo-specific rules, are in our Ontario CO alarm rules 2026 guide.

Ductwork matters: return balancing and sealing

No air quality equipment performs to its rating if the duct system delivering that air is leaky, poorly balanced, or blocked. Typical residential ducts leak 20 to 30 percent of conditioned air into attics, crawl spaces, and wall cavities. Those same leaks pull unfil- tered air (including insulation fibres, attic dust, and radon- contaminated soil gas in basement ducts) into the return side.[5]

Ontario duct cleaning runs $300 to $600 for a typical home, but Health Canada and most independent reviews find duct cleaning has limited measurable health benefit unless there is visible mould, vermin, or debris blocking airflow.[2] If your concern is allergens or dust, the money is better spent on better filter media and a properly sized HRV.

Duct sealing is a different story. Professional sealing (manual or aerosol-based, such as Aeroseal) costs $1 to $2 per square foot, or $1,000 to $6,000 for a typical whole-home project. Sealing can improve HVAC efficiency by up to 20 percent and dramatically reduces the amount of unfiltered air the return side pulls in. If your furnace is more than 15 years old and you have never had the ducts sealed, this is a higher-impact air quality upgrade than most filtration add-ons.

Full duct replacement runs $1,400 to $9,000 depending on home size and complexity. This is rarely justified by air quality alone, but makes sense alongside a full HVAC replacement or a major renovation.

Priority order: where to spend first

If you are starting from scratch and want the most indoor air quality per dollar, spend in this order:

1. Radon test. $30 to $70 for a long-term kit, run through a heating season. If you are above 200 Bq/m3, mitigate before anything else on this list. If you are below, check this item off and move on.[1]
2. CO and smoke alarms to 2026 code. Verify layout, replace any alarm older than 10 years, add units to meet the January 2026 Fire Code. $40 to $100 per alarm.[6]
3. Furnace filter upgrade to MERV 11 to 13. $40 to $100 per filter, changed every three months. Better particle and smoke capture with no system modification in most cases.
4. Portable HEPA unit(s) for the bedroom and main living area. $100 to $800 per unit. Covers the rooms where you actually spend your time.[2]
5. HRV install (if the home does not already have one).$2,500 to $5,000 installed. The biggest real air quality upgrade most older Ontario homes can get.[10]
6. Duct sealing. $1,000 to $6,000 depending on home size. High impact, often skipped.
7. Only then, if you still have budget: whole-home HEPA, premium filtration cabinets. UV-C and PCO generally do not earn a place on this list based on current evidence.[3]

The honest summary: source control (radon mitigation, CO alarms, keeping pollutants out), ventilation (HRV, kitchen and bathroom exhaust), and filtration (MERV 11 to 13 plus portable HEPA) will handle the indoor air quality concerns of 95 percent of Ontario homes. The expensive marketing-heavy add-ons mostly do not.

Frequently Asked Questions