What Is ASHRAE 62.2 and Why It Matters for Your Home

There is a national standard that defines exactly how much fresh air your home should be getting. It specifies the minimum ventilation rate based on your home's size and how many people live in it. It has been developed and refined over decades by the leading professional organization in heating, ventilation, and air conditioning engineering.

Most homeowners have never heard of it. And most older homes in Maine do not come close to meeting it.

The standard is ASHRAE 62.2, published by the American Society of Heating, Refrigerating and Air-Conditioning Engineers. It is titled "Ventilation and Acceptable Indoor Air Quality in Residential Buildings," and understanding what it calls for - and why - can change how you think about the air in your home.

What ASHRAE 62.2 Requires

The standard establishes a minimum whole-building ventilation rate based on a formula:

Total ventilation = 0.03 CFM per square foot of floor area + 7.5 CFM per occupant

CFM stands for cubic feet per minute - the volume of air moved per minute. The number of occupants is calculated as the number of bedrooms plus one (so a three-bedroom home assumes four occupants, regardless of how many people actually live there).

For a typical 1,800-square-foot, three-bedroom home in Greater Portland, the calculation looks like this:

• Floor area component: 1,800 x 0.03 = 54 CFM
• Occupant component: 4 x 7.5 = 30 CFM
• Total required: 84 CFM of continuous ventilation

That means 84 cubic feet of fresh outdoor air needs to enter the home every minute, and an equivalent volume of stale indoor air needs to leave. Continuously. Not just when someone remembers to open a window or turn on a fan.

Local Exhaust Requirements

In addition to whole-building ventilation, ASHRAE 62.2 requires local exhaust in areas where pollutants are generated:

• Bathrooms: 50 CFM intermittent or 20 CFM continuous
• Kitchen: 100 CFM intermittent (vented range hood) or 5 air changes per hour continuous

These local exhaust rates are separate from and in addition to the whole-building ventilation rate. The idea is straightforward: remove pollutants at the source (bathroom moisture, cooking fumes) before they spread through the house, and provide general dilution ventilation for the remaining pollutant load.

How Most Maine Homes Fall Short

No Mechanical Ventilation System

The most common ventilation "system" in older Maine homes is no system at all. The home relies entirely on air leakage through the building envelope for fresh air exchange. This approach has three problems:

The rate varies wildly. On a windy day, a leaky home might exchange air multiple times per hour. On a calm, mild day, the exchange rate drops to near zero. ASHRAE 62.2 calls for a consistent, reliable ventilation rate - not one that depends on weather conditions.

The air comes from contaminated sources. In a leaky home, replacement air enters through the basement, crawlspace, wall cavities, and attached garage via the stack effect. This air carries moisture, mold spores, radon, VOCs from stored chemicals, and other contaminants. ASHRAE 62.2 assumes ventilation air comes from outdoor sources, not from the dirtiest spaces in the building.

There is no filtration. Air leaking through building cavities picks up dust, insulation particles, and biological contaminants along the way. Mechanical ventilation can include filtration. Air leakage cannot.

Exhaust-Only Bathrooms with Poor Performance

Many older homes have bathroom exhaust fans that were installed to code at the time of construction or renovation. But "installed" does not mean "functioning adequately." Common issues:

• Undersized fans. A 50 CFM fan in a large bathroom may not be adequate.
• Degraded performance. Fan motors lose capacity over time. A 10-year-old fan often moves half the air it did when new.
• Poor ductwork. Flexible vinyl ducts that sag, kink, or terminate in the attic instead of outdoors reduce delivered airflow to a fraction of the fan's rated capacity.
• Nobody turns them on. Bathroom fans only work when someone operates them. Intermittent use does not provide the continuous air exchange ASHRAE 62.2 envisions.

No Kitchen Exhaust to Outdoors

As we discussed in our kitchen range hood post, roughly two-thirds of homes have recirculating range hoods that do not vent to the outside. These do not count toward ASHRAE 62.2 local exhaust requirements because they do not remove pollutants from the building - they recirculate them.

Why This Standard Exists

ASHRAE 62.2 was first published in 2003 and has been updated multiple times since. It exists because decades of indoor air quality research demonstrated that homes with inadequate ventilation have higher concentrations of:

• CO2 from occupant breathing, causing drowsiness and reduced cognitive function
• Moisture, leading to mold, dust mite proliferation, and structural damage
• Formaldehyde and other VOCs from building materials, furnishings, and household products
• Radon from soil gas infiltration (Maine has among the highest radon levels in the U.S.)
• Particulates from cooking, cleaning, and combustion appliances
• Biological allergens including mold spores, dust mite proteins, and pet dander

The standard sets ventilation rates that research shows are sufficient to keep these pollutant concentrations below levels associated with health effects in the general population. It is a minimum standard, not an optimum - more ventilation is generally better, within practical limits.

How ASHRAE 62.2 Applies to Existing Homes

ASHRAE 62.2 is a standard, not a building code. However, it has been adopted by reference in many building codes and is the benchmark used by programs like:

• Building Performance Institute (BPI) certification, which governs the weatherization work we do at Horizon Homes
• ENERGY STAR for Homes, which requires compliance with 62.2 for new construction
• Efficiency Maine weatherization programs, which reference BPI standards

For existing homes, ASHRAE 62.2 applies most directly during weatherization work. When a contractor air seals and insulates a home, they are reducing the air leakage that the home previously relied on for ventilation (however poorly). BPI standards require the contractor to evaluate whether mechanical ventilation is needed to meet ASHRAE 62.2 after the air sealing work is completed.

This is one of the most important reasons to work with a BPI-certified contractor for weatherization work. An insulation installer without BPI training may seal up air leaks without considering the ventilation implications. A BPI-certified contractor evaluates the home as a system and ensures that air sealing and ventilation are addressed together.

Ventilation Strategies That Meet ASHRAE 62.2

Exhaust-Only Ventilation

The simplest and least expensive approach. A quiet, continuous-run bathroom exhaust fan pulls stale air out of the home at the required rate. Replacement air enters through the remaining air leaks in the envelope, or through a small passive air intake if the home is tight enough to need one.

Pros: Low cost, simple installation, easy to maintain. Works well for moderately tight homes.

Cons: Depressurizes the home slightly, which can pull air from undesirable sources (garage, crawlspace) if the envelope is not well sealed. No heat recovery - warm air is exhausted and replaced with cold outdoor air.

Best for: Retrofit projects on moderately leaky existing homes where the budget for ventilation is limited.

Supply-Only Ventilation

A fan or duct brings outdoor air into the home, often connected to the heating system's air handler. Stale air exits through the remaining air leaks and local exhaust fans.

Pros: Pressurizes the home slightly, preventing infiltration of contaminated air from basements and garages. Outdoor air can be filtered before entering living spaces.

Cons: No heat recovery. The incoming cold air must be tempered by the heating system, adding to energy costs.

Best for: Homes with combustion appliances where depressurization from exhaust-only ventilation could cause backdrafting.

Balanced Ventilation with Heat Recovery (HRV/ERV)

A heat recovery ventilator (HRV) or energy recovery ventilator (ERV) exhausts stale air and brings in fresh air simultaneously through a heat exchanger that transfers 70-85% of the heat from the outgoing air to the incoming air.

Pros: No pressure imbalance. Heat recovery reduces the energy penalty of ventilation. Incoming air can be filtered. Provides the most consistent and controlled ventilation of any approach.

Cons: Higher installation cost. Requires ductwork. Filters and heat exchanger cores need regular maintenance.

Best for: Tight homes (below 5 ACH50) in cold climates. This is the gold standard for Maine homes that have been comprehensively air sealed.

The Differences Between HRV and ERV

An HRV transfers heat only. An ERV transfers both heat and moisture. In Maine's dry winter climate, an ERV can help retain indoor humidity that would otherwise be exhausted, keeping the home more comfortable without a supplemental humidifier. For most Maine homes, either an HRV or ERV is appropriate - the choice depends on specific moisture conditions and occupant preferences.

The ASHRAE 62.2 Credit for Infiltration

One provision of the standard that is directly relevant to existing homes: ASHRAE 62.2 allows a credit for air infiltration. If blower door testing shows that the home has a natural infiltration rate above a certain threshold, the required mechanical ventilation rate is reduced by the amount of infiltration that exceeds the threshold.

In practice, this means that a moderately leaky home after air sealing (say, 5 ACH50) may need less mechanical ventilation than a home sealed to Passive House levels (0.6 ACH50). The standard accounts for the reality that some air leakage will persist in virtually all existing homes, and credits that leakage toward the ventilation requirement.

This infiltration credit is calculated using blower door data and climate-specific factors. It is another reason why blower door testing - which we use at the start and end of air sealing work to measure results - is essential for designing an appropriate ventilation strategy.

What This Means for Your Home

If your home is like most older homes in Portland, South Portland, Westbrook, Scarborough, or other Greater Portland communities, it likely has:

• No mechanical ventilation system
• Bathroom exhaust fans that may or may not function adequately
• No vented kitchen exhaust
• High air leakage rates that provide uncontrolled, contaminated "ventilation"

This does not mean your home is in crisis. Millions of homes operate this way. But it does mean that your indoor air quality during heating season is almost certainly worse than it would be with a proper ventilation strategy, and that your home is wasting energy by exchanging air through the dirtiest, least efficient pathways possible.

The path to better air quality and lower energy bills runs through the same work: air sealing to stop uncontrolled leakage, insulation to reduce heat loss, and controlled ventilation to provide the fresh air your family needs.

How We Apply ASHRAE 62.2 in Our Work

At Horizon Homes, we have been working on Greater Portland homes since 2006. Our technicians are BPI-certified, and we follow BPI standards that incorporate ASHRAE 62.2 requirements for every weatherization project. This means:

• We measure air leakage before and after air sealing using blower door testing
• We calculate the ventilation requirement for each home based on size and occupancy
• We evaluate existing ventilation (bathroom fans, kitchen exhaust) for adequacy
• We recommend and can install mechanical ventilation when the home requires it post-air sealing

This is not an optional step or an add-on. It is part of how the work is done correctly.

Schedule your free energy assessment or call (207) 221-3221 to start the conversation. Rebates through Efficiency Maine can offset a portion of the project cost, and amounts are income-dependent.