Mechanical ventilation is an essential feature of high performance homes. Ventilation is needed for source control at the location of contaminant sources (e.g. kitchens, bathrooms, craft areas) as well as for distribution of fresh air and dilution of general contaminants. The distribution of fresh air and dilution of general contaminant is referred to as "background" or "whole- house" ventilation.

The 2012 International Residential Code (2012 IRC) provides code minimum requirements for ventilation systems including the ventilation rate capacity for both background/whole house ventilation and source control ventilation. This guide aims to provide additional guidance toward meeting the high performance objectives of DER projects.

Source Control Ventilation

Controlling contaminants at the source is the most effective means to control contaminants in a home. Source control ventilation systems are exhaust systems that are located near a fixed contaminant source (or fixed contaminant source location) and vented directly to the outdoors. There can be a number of different areas in a home that represent a need for source control ventilation. This guide addresses those areas requiring source control that are common to all homes: kitchens and bath/toilet rooms.

Bathroom exhaust

Exhaust ventilation in bathrooms is needed to control odors and excess humidity. The bathroom exhaust system typically benefits from a door that can be closed to help contain indoor contaminants and make the exhaust ventilation more effective. A bathroom exhaust ventilation system that is operated intermittently (e.g. by a manual switch or humidity control) must have a capacity to exhaust at a rate of at least 50 cfm. Where the exhaust system is operated manually, it is a good idea to use a delay-off switch or crank timer to operate the bathroom exhaust system for a set period of time after use without having the system run continuously.

A bathroom exhaust may also be provided by a ventilation system that operates continuously. The minimum acceptable exhaust rate for a continuously operating system is 20 cfm. However, this ventilation rate is not likely to prevent fogging of mirrors or to rapidly clear steam and odors from a bathroom.

Kitchen exhaust

Cooking releases volatile compounds into the air. Cooking is also a source of moisture. Gas cooking appliances produce large amounts of moisture and carbon dioxide and can also contribute other products of combustion. On occasion, cooking - even by experienced cooks or bakers - will produce smoke. Source control exhaust ventilation in a kitchen is needed to control these contaminants. The kitchen exhaust can also benefit the indoor environment and energy performance of the home during cooling periods by reducing the amount of heat that cooking contributes to the interior.

To be effective, the source control exhaust should be conducted through a capture hood located as close as feasible to the cooking surface - closer to the cooking surface provides better capture of contaminants but too close detracts from the usability of the cooking surface. The minimum acceptable ventilation rate capacity of a kitchen exhaust system is 100 cfm.

The Home Ventilating Institute (HVI) recommends 100 cfm for per lineal foot of cooktop for wall-mounted hoods and 150 cfm per lineal foot of cooktop for island hoods. HVI recommends additional capacity for gas cook tops based on capacity of the burners. While higher exhaust rates can improve source control, one should also consider the energy and make-up air implications of higher exhaust rates. For example, the 2012 IRC requires makeup air for exhaust hood systems capable of exhausting in excess of 400 cfm.

Background or Whole-house Ventilation

Background or whole-house ventilation is needed to provide distribution of fresh air as well as dilution of general contaminants. General contaminants, in this context, are those that derive from things that are widespread, such as building finishes and furnishings, or that move, such as people and pets. The keys to effective background/whole house ventilation are adequate capacity, appropriate control, and effective distribution.

The required ventilation rate capacity indicated in the 2012 IRC for background/whole house ventilation is determined from the number of bedrooms and the conditioned floor area of the dwelling unit (i.e. home or apartment). The relevant table in the 2012 IRC is derived from the following formula:

Q = (Nbr+1) x 7.5 + 0.01 x FA

Where

Q = the continuous ventilation rate in cubic feet per minute (cfm), Nbr = the number of bedrooms, and

FA = the conditioned floor area in square feet (sf).

While the IRC addresses the design capacity of the ventilation system, it does not dictate how the system is operated. BSC recommends that background/ whole house ventilation systems be designed and installed to provide a ventilation capacity that is 125-200% of the ventilation rate given by the formula above and that the controls of the ventilation system allow it to be operated at a lower rate most of the time. BSC's experience has shown that satisfactory indoor air quality and moisture control is typically achieved with a background/whole house ventilation rate that is 30-60% of the rate given by the formula above. Certain situations, however, such as large gatherings, cooking mishaps, installation of new furnishings, hockey players returning from practice, etc. may require much higher ventilation rates on a temporary basis.

Operating the ventilation system at a rate that is too low is typically noticeable to occupants by signs such as condensation on windows, accumulation of odors, or feeling of "stuffiness". Operating the ventilation system at a higher rate than needed wastes energy and can lead to undesirable decrease or increase in indoor humidity. In many cases, however, excessive ventilation may not be noticeable-except on energy bills. The controls for the ventilation system should allow residents to operate the system at a lower rate when the lower rate is adequate and also to boost the ventilation rate on a temporary basis when a higher rate of ventilation is needed.

Another critical parameter of the ventilation system that the IRC does not address is distribution. A single point exhaust or supply ventilation system may provide adequate distribution of fresh air in a smaller home with a compact and open floor plan and where doors are left open. In most residential situations, some form of ventilation distribution is needed. Dedicated ventilation ductwork can ensure effective distribution of the ventilation air and provide a measure of air mixing with operation of the ventilation system. Mixing of interior air is also important for comfort and temperature uniformity. Periodic mixing of the interior air allows the conditioning systems (i.e. heating, cooling, dehumidification, filtration) of the home to better condition the interior air. The distribution and air mixing can be achieved by a separate system such as a ducted forced-air heating/cooling system in which the air handler fan is periodically cycled on. A ventilation system may also be integrated with a ducted central heating/cooling system to use the central system fan and ductwork to provide distribution of ventilation air and mixing of the interior air.

Ventilation System Schematics

On the following pages are schematic descriptions of four ventilation system configurations that can provide effective ventilation in DER homes. These configurations are designated as:

• Ventilation System 1 - balanced heat recovery or energy recovery ventilation with dedicated ductwork
• Ventilation System 2 - balanced heat recovery or energy recovery ventilation integrated with forced-air heating and cooling.
• Ventilation System 3 - supply ventilation integrated with the central fan of a forced-air heating and/or cooling system. This is also called central-fan-integrated supply ventilation or CFIS ventilation.
• Ventilation System 4 - non-distributed exhaust-only or balanced ventilation.

Ventilation System 1: Balanced heat/energy recovery ventilation with dedicated ductwork

This system consists of heat- or energy recovery ventilation equipment with dedicated ventilation distribution ductwork. Two variations of this system are defined by the direction of ventilation with respect to the bedrooms. Ventilation System 1a locates ventilation air returns (stale air pick-up) in bedrooms. Ventilation System 1b locates ventilation air supply registers in bedrooms.

Required Attributes	Outside air intake through side wall, above expected snow depth and away from contaminant sources (see BSC Info Sheet 606: Placement of Intake and Exhaust Vents available from www.buildingscience. com). Controls: timer for intermittent operation if system does not otherwise allow user to adjust between IRC background/whole house ventilation rates and lesser ventilation rates. Minimum 60% sensible recovery.
Recommended Attributes	High efficiency fan motors in HRV/ERV unit. Separate bathroom exhaust.
Performance Verification	Measure and record the ventilation airflow through the outdoor air duct. Compare to within the lesser of +/- 10% or 10 cfm of the design airflow.
Advantages	Uses known and controlled source of ventilation air. Provides ventilation distribution and air mixing. Heat/energy recovery on background/whole house ventilation. Operation is independent of heating/cooling system. Opportunity for filtration of ventilation air (depending upon HRV/ ERV unit).
Disadvantages/ Challenges	Higher installation cost. May be difficult to locate distribution ductwork in retrofit situation.
Additional Considerations	Some HRV/ERV units use significant electrical energy to recover a modest amount of thermal energy. Total system fan efficacy is important criteria in selection of HRV/ERV equipment. Good total system fan efficacy is < 1 Watt per cfm. Better total system fan efficacy is <0.5 Watt per cfm. HRV/ERV units require a modest amount of maintenance to keep intake and exhaust grilles clear (interior and exterior) and to periodically change the filters. Avoid comfort problems: ensure that ventilation air is not directed to beds or other locations where occupants are likely to be sedentary. An HRV/ERV will temper the ventilation air but even well tempered ventilation supply airflow will be perceived as a cool draft to a stationary person. An ERV should not be used to provide source control exhaust for bathrooms because the ERV will be less effective at removing moisture. By design, the ERV recovers moisture from the exhaust stream.

Ventilation System 2: Balanced heat/energy recovery ventilation integrated with forced-air heating and cooling

This system employs a heat- or energy recovery unit that is connected to the ductwork of a ducted forced-air central heating/cooling system. This system is only applicable to situations where there is a ducted forced-air central heating/cooling system. Two variations of this approach are defined by whether the ventilation system is connected to both the supply and return plenum of the central heating/cooling system - Ventilation System 2a - or whether the ventilation system is connected to the return plenum only - Ventilation System 2b.

Required Attributes	Outside air intake through side wall, above expected snow depth and away from contaminant sources (see BSC Info Sheet 606: Placement of Intake and Exhaust Vents available from www.buildingscience. com). Motorized dampers or backdraft dampers between HRV/ERV and central system supply/return plenum that close the connection to the outside when the ventilation fan is off. Controls: timer for intermittent operation if system does not otherwise allow user to adjust between IRC background/whole house ventilation rates and lesser ventilation rates. Minimum 60% sensible recovery. Ventilation System 2a: Interlock control to operate air handler with HRV/ERV. Separate bathroom exhaust.
Recommended Attributes	High efficiency fan motors in HRV/ERV unit and central air handler. Controls: ventilation control, timer to coordinate HRV/ERV operation with air handler heating/cooling operation in order to achieve full distribution with minimal fan energy. Ventilation System 2b: Separate bathroom exhaust.
Performance Verification	Measure and record the ventilation airflow through the outdoor air duct. Compare to within the lesser of +/- 10% or 10 cfm of the design airflow.
Advantages	Uses known and controlled source of ventilation air. Provides ventilation distribution and air mixing when operation is coordinated with central air handler operation. Heat/energy recovery on background/whole house ventilation. Opportunity for filtration of ventilation air (depending upon HRV/ ERV unit). Operation is independent of source control exhaust (applies to Ventilation System 2a, may also apply to 2b).
Disadvantages/ Challenges	Higher installation cost. May result in higher electrical energy use for ventilation due to the need to use the HRV/ERV and central air handler fans for distribution. Ventilation System 2a requires interlock with air handler unit fan to provide distribution. Because the HRV/ERV provides connections between the pressurized/depressurized heating and cooling ductwork, tight closing dampers are needed to prevent the HRV/ERV from acting as gross duct leakage.
Additional Considerations	Some HRV/ERV units use significant electrical energy to recover a modest amount of thermal energy. Total system fan efficacy is important criteria in selection of HRV/ERV equipment. Good total system fan efficacy is < 1 Watt per cfm. Better total system fan efficacy is <0.5 Watt per cfm. HRV/ERV units require a modest amount of maintenance to keep intake and exhaust grilles clear (interior and exterior) and to periodically change the filters. Avoid comfort problems: ensure that ventilation air is not directed to beds or other locations where occupants are likely to be sedentary. Even room temperature airflow could be perceived as a cool draft. An HRV/ERV will temper the ventilation air but the tempered ventilation air will be cooler than room air in cold weather. An ERV should not be used to provide source control exhaust for bathrooms because the ERV will be less effective at removing moisture. By design, the ERV recovers moisture from the exhaust stream.

Ventilation System 3: Central Fan-Integraged Supply (CFIS) Ventilation

This system uses an outdoor air duct, a motorized damper and supplemental air handler fan control to provide and distribute a controlled amount of ventilation through the ductwork of a ducted forced-air central heating/cooling system. This ventilation system is only applicable to situations where there is a ducted forced- air central heating/cooling system. For additional description of this ventilation system see BSC Information Sheet 610: Central Fan Integrated Ventilation Systems available from www.buildingscience.com.

Required Attributes	6" diameter (min.) insulated outdoor air duct connected to return plenum not closer than 3 feet to the air handler unit inlet. There should be no take-off or branch on the return between the outdoor air duct connection and the air handler unit inlet. Outside air intake through side wall, above expected snow depth and away from contaminant sources (see BSC Info Sheet 606: Placement of Intake and Exhaust Vents available from www.buildingscience. com) Fan cycling control to operate the air handler fan a programmed minimum amount of time as determined by the desired ventilation rate and the rate of intake through the outdoor air duct. Motorized damper in outdoor air duct controlled by the fan cycling control to close the damper and prevent over ventilation of the house during times of significant space conditioning demands. Balancing damper in outdoor air duct between motorized damper and connection to return plenum to allow adjustment of ventilation airflow rate.
Recommended Attributes	High efficiency central air handler fan motor.
Performance Verification	Measure and record the ventilation airflow through the outdoor air duct with the air handler operating at both heating and cooling speeds. Compare to within the lesser of +/- 10% or 10 cfm of the design airflow.
Advantages	Uses known and controlled source of ventilation air. Provides ventilation distribution and air mixing. System operation is independent of source control exhaust. Opportunity for filtration of ventilation air. Relatively low installed cost.
Disadvantages/ Challenges	In low load homes, CFIS may result in higher electrical energy use for ventilation due to operation of central air handler fan for distribution.
Additional Considerations	Outdoor air should not exceed 15% of total air handler return air flow. Outside air duct should be positioned so that there is a fall/slope toward the outside to drain any potential condensation due to blown snow. CFIS controls may not be compatible with HVAC equipment that uses proprietary wiring such as in many mini-split systems. Avoid comfort problems: ensure that supply registers do not direct air to beds or other locations where occupants are likely to be sedentary. Even room temperature airflow could be perceived as a cool draft. Ventilation air from the CFIS is tempered with air handler return air but the mixed air will be cooler than room air in cold weather.

Ventilation System 4: Non-distributed exhaust-only or balanced ventilation

This system uses either exhaust-only ventilation (Ventilation System 4a) or balanced ventilation (Ventilation System 4b) with a single point distribution. These configurations are appropriate only in situations where either 1) the floor plan is open and compact and interior doors between rooms are seldom closed, or 2) there is a ducted heating/cooling system with an air handler fan that can be cycled to provide ventilation air distribution.

Required Attributes	Fan control to operate ventilation fan as needed to achieve desired ventilation rate. Manual override for operation of ventilation fan. Compact and open floor plan OR ducted forced-air heating or cooling system with fan cycling control on central air handler. Ventilation System 4a: Use of this system requires monitoring for radon. Implementation of soil gas venting is strongly recommended if this ventilation system is employed. Ventilation System 4b: Outside air intake through side wall, above expected snow depth and away from contaminant sources (see BSC Info Sheet 606: Placement of Intake and Exhaust Vents available from www.buildingscience. com). Supply or return grille must be located in non-enclosed central space.
Recommended Attributes	Fan cycling control for central air handler to provide ventilation air distribution: 50-70% recirculation turnover, or cycle central fan on for at least 10 minutes per hour.
Performance Verification	Measure and record the ventilation airflow through the exhaust grille (Ventilation System 4a) or outdoor air duct (Ventilation System 4b). Compare to within the lesser of +/- 10% or 10 cfm of the design airflow.
Advantages	Low installed cost.
Disadvantages/ Challenges	Source of ventilation air is unknown and uncontrolled (Ventilation System 4a). System does not provide air mixing or distribution of ventilation air. May result in higher electrical energy use for ventilation due to operation of central air handler fan for distribution.
Additional Considerations	Exhaust air duct should be positioned so that there is a fall/slope toward the outside to drain any potential condensation. External fan cycling controls may not be compatible with HVAC equipment that uses proprietary wiring such as the case with many mini-split systems. Ventilation System 4a: If exhaust fan is located in a bathroom/toilet room, the door should be left open when the room is not in use. Special attention to prevent problems such as intake of soil gases (see Soil Gas Control below) or intake of air from an attached garage.