ERV and HRV Ventilation Systems: Cost for Tight Homes

Why Tight Homes Need Mechanical Ventilation

Modern building practices and energy codes have made homes significantly more airtight than older construction. While this dramatically improves energy efficiency, it creates a ventilation problem. Older homes with drafty windows, gaps around doors, and poorly sealed walls exchanged their entire volume of indoor air every one to two hours through uncontrolled leakage. This was wasteful from an energy standpoint, but it provided constant fresh air. A tightly built modern home may exchange its air only once every four to ten hours through natural leakage, which is not enough to dilute indoor pollutants, remove excess moisture, and maintain healthy CO2 levels.

ASHRAE Standard 62.2 specifies the minimum ventilation rate for homes based on floor area and number of bedrooms. For a typical 2,000 square foot, three bedroom home, the standard calls for about 60 to 75 cubic feet per minute (CFM) of continuous ventilation. Meeting this standard through natural leakage alone requires an air leakage rate that would defeat the purpose of tight construction. The solution is controlled mechanical ventilation, specifically an ERV or HRV that provides the required fresh air flow while recovering most of the energy that would otherwise be lost.

HRV vs ERV: Understanding the Difference

Both HRVs and ERVs use a heat exchanger core where outgoing and incoming airstreams pass close to each other without mixing. The core transfers energy from the warmer stream to the cooler stream, pre conditioning the incoming air before it enters the home. The fundamental difference is what type of energy each transfers.

HRVs transfer only sensible heat (temperature). In winter, the warm outgoing air heats the cold incoming air. In summer, the cool outgoing air precools the hot incoming air. HRVs use a metal or plastic plate core with separate channels that keep the airstreams physically isolated. This means HRVs do not transfer moisture between the streams, the incoming air retains whatever humidity level the outdoor air has.

ERVs transfer both sensible heat and latent heat (moisture). The core uses a permeable membrane (typically an enthalpic polymer or treated paper) that allows water vapor molecules to pass through along with heat. In winter, the outgoing humid indoor air transfers some of its moisture to the dry incoming air, which helps maintain indoor humidity. In summer, the incoming humid outdoor air transfers some of its moisture to the drier outgoing air before entering the home, which reduces the dehumidification load on the air conditioner.

Which Type for Which Climate

HRVs are best for cold, dry climates (northern U.S., Canada) where the primary concern is recovering heat in winter and the outdoor air in summer is not excessively humid. In these climates, moisture transfer is less important because winter outdoor air is already very dry and you want a humidifier to add moisture anyway, not recover it from the stale outgoing air. The lower cost of HRVs ($1,300 to $2,400) makes them the value choice in these regions.

ERVs are best for hot, humid climates (Southeast, Gulf Coast, Mid Atlantic) where summer humidity is a major concern. The moisture transfer capability of an ERV prevents humid outdoor air from adding to the indoor moisture load, reducing the work your air conditioner and dehumidifier have to do. In winter (which is milder in these regions), the ERV still recovers heat while also retaining some indoor moisture. ERVs cost more ($2,750 to $8,000) but provide better overall performance in climates with significant humidity challenges.

Mixed humid climates (much of the central and eastern U.S.) are well served by either type, but ERVs provide a slight edge because they help in both seasons. The higher cost may or may not be justified depending on how severe your humidity problems are. If your home already has good humidity control through other means (dehumidifier, properly sized AC), an HRV provides the ventilation benefit at lower cost.

Installation and Cost Details

Both systems require two penetrations through the exterior wall, one for incoming fresh air and one for exhaust. The unit itself typically mounts in the basement, utility room, or attic and connects to the ductwork through dedicated supply and return connections. In homes with existing ductwork, the ERV or HRV can be tied into the HVAC duct system to distribute fresh air through the existing registers. In homes without ductwork (hydronic heating, for example), dedicated ventilation ductwork must be installed, which increases cost significantly.

Installation labor accounts for a large portion of the cost because it involves cutting and connecting ductwork, mounting the unit, running condensate drains (HRVs produce condensate in winter as the outgoing moist air contacts the cold core), wiring controls, and balancing the airflow to match the ASHRAE ventilation requirement for the home. A straightforward installation tied into existing ductwork takes four to eight hours. A custom installation with new ductwork can take two to three days.

Annual maintenance involves cleaning or replacing the filters in the unit (every three to six months), cleaning the heat exchange core annually (most cores can be washed with water), checking and clearing the condensate drain, and inspecting the exterior intake and exhaust hoods for blockage. Filter replacements cost $20 to $50 per set, and the annual maintenance is simple enough for most homeowners to handle without professional help.

Operating costs are modest. The fans in an ERV or HRV typically consume 40 to 100 watts when running continuously, adding $35 to $90 per year to your electricity bill. However, the energy recovered from the outgoing air offsets a much larger amount of heating or cooling energy, so the net effect on total energy costs is usually a savings of $100 to $300 per year compared to ventilating by opening windows or running exhaust fans.