UPDATED on March 13, 2015
Balanced Ventilation Is Appropriate for All Climates
Bird's eye view
Supply and exhaust fans working in cooperation
Balanced systems typically have two fans and two duct systems, one for supply air and one for exhaust air. Ductwork can be extensive, with supply ducts to provide fresh air to bedrooms and living areas and exhaust ducts to remove stale air from bathrooms, laundry rooms, and sometimes kitchens.
Avoid flex duct if possible
The best duct material for ventilation supply ducts is galvanized steel; flex duct should be avoided or minimized. Some installers use PVC pipe for exhaust ducts.
Heat recovery systems do a better job
While ASHRAE 62.2A standard for residential mechanical ventilation systems established by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers. Among other requirements, the standard requires a home to have a mechanical ventilation system capable of ventilating at a rate of 1 cfm for every 100 square feet of occupiable space plus 7.5 cfm per occupant. ventilation requirements can be met with an exhaust-only or supply-only ventilation system, the performance of these lower-cost ventilation systems will not equal the performance of a properly installed HRV.
Getting the most out of an HRV
If the budget allows, HRV installations should always include dedicated ventilation ductwork. Such systems are routinely installed in New England homes with hydronic heating systems. Ventilation ducts usually measure 4 inches in diameter. Because air flows and pressures are much lower than those encountered in a forced-air heating system, meticulous duct sealing is essential.
Homes equipped with an HRV do not need bathroom exhaust fans, since the HRV draws its exhaust air from bathrooms and laundry rooms. Each bathroom can be equipped with an override switch to operate the HRV at high speed for odor removal. An HRV should never pull exhaust air from a range hood, since grease can clog an HRV.
When an HRV is installed in a home with a furnace, the existing forced-air ductwork is usually used for the mechanical ventilation system. Although such systems work, they involve technical compromises that may degrade the performance and energy efficiency of the HRV. Forced-air ductwork is much larger than necessary to handle the needs of a ventilation system. If the HRV is wired to use the furnace blower motor to distribute ventilation air, energy use will be much higher than it would be if the HRV fans were used.
Keep intake air clean
Ventilation of living space is covered in Section 303 of the 2006 IRCInternational Residential Code. The one- and two-family dwelling model building code copyrighted by the International Code Council. The IRC is meant to be a stand-alone code compatible with the three national building codes—the Building Officials and Code Administrators (BOCA) National code, the Southern Building Code Congress International (SBCCI) code and the International Conference of Building Officials (ICBO) code.. Natural and mechanical Intake openings should be at least 10 feet from any potential source of contamination like exhaust vents, plumbing vents, streets, alleys, chimneys, parking lots, and loading docks. When the contaminant is within 10 feet, the intake vent must be located at least to feet below the source of contamination (303.4.1). Intake and exhaust openings must be protected with corrosion-resistant grills, screens or louvers with a hole size between 1/4 and 1/2 in.
ABOUT BALANCED VENTILATION
Supplying fresh air while exhausting stale air
A balanced ventilation system uses a supply fan to introduce the same volume of fresh outdoor air that is being simultaneously removed from the house by an exhaust fan. These systems are more complex than supply-only or exhaust-only ventilationMechanical ventilation system in which one or more fans are used to exhaust air from a house and make-up air is supplied passively. Exhaust-only ventilation creates slight depressurization of the home; its impact on vented gas appliances should be considered. systems, but provide better fresh air distribution and in some cases lower energy bills than alternative systems.
MORE ABOUT BALANCED VENTILATION
Heat-recovery ventilators and energy-recovery ventilators
The most sophisticated types of balanced ventilation systems incorporate either heat recovery or energy recovery, offsetting some of the energy penalty associated with bringing in fresh air from the outside. In winter, fresh air pulled into the house is warmed by outgoing air in a heat exchangerDevice that transfers heat from one material or medium to another. An air-to-air heat exchanger, or heat-recovery ventilator, transfers heat from one airstream to another. A copper-pipe heat exchanger in a solar water-heater tank transfers heat from the heat-transfer fluid circulating through a solar collector to the potable water in the storage tank. that is capable of capturing 60% to 80% of the heat. If the house is air conditioned, summer exhaust air may cool incoming fresh air before it’s circulated in the house.
The two systems are similar, although an energy-recovery ventilator (ERVEnergy-recovery ventilator. The part of a balanced ventilation system that captures water vapor and heat from one airstream to condition another. In cold climates, water vapor captured from the outgoing airstream by ERVs can humidify incoming air. In hot-humid climates, ERVs can help maintain (but not reduce) the interior relative humidity as outside air is conditioned by the ERV.) has the additional capability of transferring some of the moisture in the air as well as heat. A heat-recovery ventilator (HRV(HRV). Balanced ventilation system in which most of the heat from outgoing exhaust air is transferred to incoming fresh air via an air-to-air heat exchanger; a similar device, an energy-recovery ventilator, also transfers water vapor. HRVs recover 50% to 80% of the heat in exhausted air. In hot climates, the function is reversed so that the cooler inside air reduces the temperature of the incoming hot air. ) transfers only heat. ERVs help retain humidity in indoor air in winter, potentially making a house more comfortable. However, research has shown that ERVs do not provide lower levels of indoor humidity in air-conditioned houses when compared to HRVs.
HRV and ERV systems are more complex, more expensive, and require more maintenance than balanced ventilation systems without heat recovery. Moreover, not all HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. contractors know how to install them.
However, they offer significant energy savings compared to ventilation systems without heat recovery.
In 2014, a small manufacturing company in Illinois (Build Equinox) began selling a new type of balanced ventilation appliance called the CERV. For information on the CERV, see A Balanced Ventilation System With a Built-In Heat Pump.
HRV or ERV?
If you're set on installing a balanced ventilation system, which type of equipment should you choose, an HRV or an ERV? For more information on solving this dilemma, see "HRV or ERV?"
- / Fine Homebuilding
- Chris Green/Fine Homebuilding
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