The most common and natural way to ventilate older houses always has been with open windows and doors. But much of the time that isn’t possible because the temperature is too warm or too cold outside — and opening windows also will allow the heated or cooled air in the house to escape. In addition, there are security issues and concern about rain coming into the house. Dust, pollen, noise and insects (and larger creatures, such as mice) also can enter through open windows and doors.
The new and optimal way to ventilate to create a modern, comfortable and healthy home is with a heat recovery ventilator (HRV) — also known as an air-to-air heat exchanger — or an energy recovery ventilator (ERV).
When new houses are built as tightly as recommended by the 2012 International Energy Conservation Code — with a maximum of three air changes per hour at 50 Pascal (3ACH50) in most states — there will be a shortage of fresh air in the house if the home is not ventilated properly. The results can include elevated carbon dioxide levels, diminished overall indoor air quality and potentially negative health consequences for the occupants.
How HRVs and ERVs Work
The HRV, or heat recovery ventilator, is an increasingly popular solution that can minimize energy loss and save on heating and cooling costs. The heated or cooled air already in the house is exchanged with fresh exterior air, while transferring some of the heat or coolness generated in the home to the incoming air.
An ERV, or energy recovery ventilator, functions in much the same way, but helps to control humidity. (ERVs are more often the ventilation choice in warm, humid climates.)
Other Benefits of Modern Ventilation Systems
An added advantage of a balanced ventilation system instead of a fan or open windows and doors is that an exchanger substantially lowers air conditioning and heating costs while reducing the size of heating and cooling equipment needed in new construction or renovations. ERVs or HRVs also can be used in combination with bathroom fans or a kitchen hood fan, but in some cases additional fans are not required.
One critical benefit of HRVs and ERVs versus exhaust fans is the controlled supply of fresh air, which remains the primary function of ventilation. Exhaust fans need additional air to compensate for the tempered stale air they are throwing outside, which is measured in CFM, or cubic feet per minute. When a negative pressure is created inside the house, fresh and often humid outside air is forced into the remaining cracks, crawl spaces and walls and most likely will not supply enough fresh air in the places it is needed most: the bedrooms and living areas.
How Ventilation Systems Have Evolved
HRVs and ERVs were introduced to the U.S. market in the 1970s but are more common in European Union countries, where strict building codes contribute to a high percentage of houses being built with ERV/HRV systems. Austria requires every house to have an ERV or HRV to meet the building code. Belgium also is likely to require the systems in the near future. In the U.S., ERVs and HRVs have become more popular in recent years with the trend toward building tighter, more energy-efficient homes.
Choosing the System That’s Right for You
When a new ERV or HRV system is installed, it is sized according to the square footage of the house, with the appropriate size typically determined by the HVAC contractor or another energy professional. The smallest units can fit in a closet or attic; larger units require more space. Small units have an airflow capacity of about 35-70 CFM (cubic feet per minute) and larger units reach about 125-350 CFM.
Units for single-family homes range in price from about $750 to more than $3000 for high-efficiency ERV units. The price can go even higher if ducting, grills, silencers, wall controls and other optional equipment is included. There also is a significant difference in cost between entry level off-the-shelf HRV units that typically are connected to an existing forced-air heating system and the new generation standalone high-efficiency continuous ventilation systems that are quieter and are custom-designed for a particular floor plan.
Toward a More Efficient Future
One of the requirements for Passive House certification is an ERV/HRV. Because the houses are so tight and have minimal air changes per hour, excellent ventilation is needed to keep the air in the house healthy. HRVs and ERVs offer continuous ventilation, recirculating all of the air every three hours, and are widely available in North America and many parts of the world. Anyone building a new house or renovating an older one should study this issue. There are other choices available, but no matter the climate, every tight home needs mechanical ventilation.
The Cronic Team of Next Generation Real Estate Services
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