Home Ventilation for Energy-Efficient Homes: HRV vs ERV Explained

Why Energy-Efficient Homes Need Whole-House Ventilation

Older homes were drafty. Air leaked in through gaps around windows, doors and joints, and that uncontrolled air exchange was their ventilation, at the cost of heat loss, drafts and cold spots. An energy-efficient home seals those gaps on purpose. That keeps heat in and drafts out, but it also means fresh air has to be brought in deliberately.

Building codes reflect this. Under the 2021 International Residential Code (Section R303.4), every home built to the energy code’s air-leakage requirements must have mechanical ventilation. Earlier editions required it once a blower-door test showed 5 air changes per hour or less at 50 pascals. Codes for colder climates can be stricter still: Larimer County, Colorado, for example, requires 3 air changes per hour or less. In Canada, Subsection 9.32.3 of the National Building Code sets the requirements for a house’s mechanical ventilation system.

Mechanical ventilation can be exhaust-only, supply-only or balanced. Exhaust-only systems pull air out with fans and let replacement air leak in wherever it can, and they can backdraft gas appliances such as draft-hood water heaters and fireplaces. Balanced systems move the same amount of air in and out through ducts, which is why we design airtight homes with balanced ventilation.

How an HRV Works

Heat recovery ventilation uses a heat recovery ventilator, often simply called an HRV system. It has two fans, filters and a heat exchanger. One fan draws stale air from the kitchen, bathrooms and laundry; the other brings fresh outdoor air in through a filter and supplies it to the living room and bedrooms. Inside the unit, the two airstreams pass each other in the heat exchanger without mixing. In winter, the outgoing warm air heats the incoming cold air; in summer, the cooler indoor air takes some heat out of the incoming air.

The system typically runs continuously at low speed. In the UK and parts of Europe it is called MVHR, mechanical ventilation with heat recovery.

HRV vs ERV: What Is the Difference?

Both an HRV and an energy recovery ventilator (ERV) have a heat exchanger, fans and controls. The difference is moisture: according to the U.S. Department of Energy, an ERV also transfers some water vapor between the airstreams, which helps keep indoor humidity more constant.

• HRV: recovers heat only. Moist indoor air is exhausted, so in winter it typically keeps the house drier.
• ERV: recovers heat and some moisture. In winter it keeps more humidity indoors, and in humid summers it typically brings less moisture in.

According to the U.S. Department of Energy, balanced ventilation is appropriate for all climates, and heat or energy recovery is most cost-effective where winters or summers are extreme and energy costs are high. In mild climates, the electricity used by the fans can outweigh the savings.

Two practical points matter for long-term performance. In cold climates the unit needs frost protection, because very cold supply air can freeze in the heat exchanger. And HRVs and ERVs need more maintenance than simpler systems: the filters and the core must be cleaned regularly, or airflow and heat recovery drop.

Which one is right depends on your climate, your household and how airtight the home is. Our Signature Plans specify an ERV, and for each project a locally licensed professional sizes the system for your climate and local code.

How Good Ventilation Supports Health and Comfort

Good ventilation removes moisture, carbon dioxide and indoor pollutants such as volatile organic compounds (VOCs) from cooking, cleaning products and furnishings. In a Harvard study of 24 office workers over six days, cognitive test scores were 101% higher in a well-ventilated, low-pollutant environment than in conventional conditions.

Humidity matters too. The EPA recommends keeping indoor relative humidity below 60%, ideally between 30% and 50%. Dust mites, the source of one of the most powerful indoor allergens, grow in damp, warm conditions, and the key to mold control is moisture control.

6 Signs of Poor Ventilation in Your Home

Recognizing the signs early lets you fix the problem before it affects your health or the house itself:

• Condensation on windows: moisture is trapped inside and can lead to mold.
• Musty odors: often a sign of mold or mildew.
• Visible mold on walls, ceilings or around windows.
• Stuffy, stale air, especially in bedrooms in the morning.
• Indoor humidity that stays above 60%, the EPA’s upper limit.
• Dust that builds up quickly, which can point to poor filtration or air circulation.

How to Improve Ventilation in an Existing Home

If you live in an existing home, these steps improve indoor air quality:

• Use exhaust fans in bathrooms and the kitchen, and make sure they vent outdoors, not into the attic.
• Open windows when the weather allows. A few minutes of cross-ventilation clears stale air.
• Control humidity with a dehumidifier in damp areas such as basements.
• Service your heating and cooling equipment, and replace filters as the manufacturer recommends.
• Use an indoor air quality monitor to track carbon dioxide and humidity.
• For a major renovation or a new home, plan a balanced ventilation system with heat recovery.

How We Plan Ventilation in Our Designs

We plan ventilation into every design from the start, because the airtight, well-insulated envelope and the ventilation system work together. Our published Signature Plans, Aurora, Solaris and Lumina, specify an energy recovery ventilator (ERV) together with ENERGY STAR exhaust fans. Read more about the envelope in our article on superior insulation and about the whole-house approach in the benefits of energy-efficient Scandinavian homes.

For your project, a locally licensed professional sizes the ventilation system for your climate and local code. To see how this works in practice, explore our Signature Plans or our custom home design service.