Choose the Whole-Building Ventilation System Type to Provide at Least the Airflow Calculated in Step 3
Whole-building ventilation provides continuous or intermittent low-flow ventilation in a home to remove general airborne contaminants from diverse sources, including finishes, furnishings, people, pets, household chemicals, and household activities. Whole-building ventilation strategies can be divided into three types:
Whole-Building Ventilation System Examples
Access a library of 16 whole-building ventilation systems that can be used to meet the whole-building ventilation requirements of ASHRAE Standard 62.2.
Best Practice Recommendations
Operating ventilation equipment uses energy, so choose equipment with the lowest possible wattage to keep operating costs low. Whole-building ventilation for a 1500 sq ft house can be provided by a 5 watt fan or a 500 watt air handler. Annual operating costs will vary significantly depending on which equipment is chosen.
It is desirable to be able to adjust the whole-building ventilation rate at the time of commissioning to ensure minimum airflow determined in Step 3. Adjustments can be made in several ways, including using a multi-speed fan, a balancing damper, or an adjustable programmable timer.
Seal all ductwork for HVAC equipment, no matter where it is located.
Exhaust-Only Ventilation Systems
Exhaust-only ventilation systems use a single-point, two-point, or multiple-point exhaust fan to provide a home or apartment's whole-building ventilation. The exhaust fan(s) removes polluted indoor air. Outdoor air enters through many small unintentional leaks in the building envelope. If the fan is located in the living space, the fan must have a sound rating of 1.0 sone or less.
Single-Point Exhaust-Only Ventilation System Features / Illustration
An exhaust fan (usually a bath fan) provides both local exhaust and whole-building ventilation plus controls that operate the fan in accordance with ASHRAE 62.2. The simplest version of this system uses an upgraded bath fan that meets the sound requirement for whole-building ventilation.
- Bath or laundry room fan set to run continuously at a low rate or intermittently at a higher rate
- Kitchen range hood with continuous low-speed setting and quiet operation (1.0 sone or less on low speed)
- Dedicated exhaust fan for whole-building ventilation
- Ducted in-line fan dedicated to whole-building ventilation
Two-Point Exhaust-Only Ventilation System Features / Illustration
- Two exhaust fans
- Single exhaust fan with two pickups
Multiple-Point Exhaust-Only Ventilation System Features / Illustration
- Three or more exhaust fans
- Single exhaust fan with multiple pickups
Title 24 Requirement
When the air handler or return duct is located in the garage, the ductwork for the HVAC system must be sealed to have air leakage of no more than 6% of the air handler airflow when measured at 0.1 in. w.c. (25 Pa) whether or not the air handler is used for ventilation.
When the air handler or return duct is located outside the pressure boundary, the ductwork for the HVAC system must be sealed to have air leakage of no more than 6% of the air handler airflow when measured at 0.1 in. w.c. (25 Pa), whether or not the air handler is used for ventilation.
Supply-Only Ventilation Systems
Supply-only ventilation systems use a dedicated fan or the air handler for the furnace or air conditioner plus appropriate controls to provide whole-building ventilation. A supply duct brings outdoor air into the house. Exhaust air exits the building through many small leaks in the building envelope. If the fan is located in the living space, the fan must have a sound rating of 1.0 sone or less.
Dedicated Supply Fan Features / Illustration
A dedicated supply fan can be installed in a mechanical space or through an exterior wall and can provide filtering and some tempering of the incoming air by mixing with the room air, either at the grille or inside the supply fan cabinet. Depending on the local climate, a blending ratio of three to one or four to one (household air to outdoor air) is necessary to maintain comfort.
Central Fan Integrated Systems (CFI) Features / Illustration
When an existing air handler is used, air must be ducted from the outside to the return side of the furnace, heat pump, or central air conditioner to provide the amount of airflow required by ASHRAE Standard 62.2 for whole-building ventilation. To lower operating costs, the air handler could be run one-third of the time, as long as it provides three times the airflow that a continuous system would provide. The air handler must operate at least once every three to four hours, 24/7 all year long – not just when heating or cooling is needed.
Upgrading to an Energy Efficient Blower Motor
When the furnace or AC air handler is used for whole-building ventilation system, the cost of providing ventilation is much higher than when a low-wattage fan is used. Blower motors usually are rated at 300 to 500 watts, with older air handlers using up to 800 to 900 watts. In recent years, energy efficient retrofit motors have been introduced that can reduce air handler energy use by 75-80%. For a system operating continuously, payback for replacing the blower motor can be as short as 3 years. Look for an ECM retrofit motor (electronically commutated motor) or a BPM retrofit motor (brushless permanent magnet motor). ECM and BPM motors use similar technology, but ECM is a trademarked name.
Keep in mind that using the air handler blower for whole-building ventilation means that the air handler will operate more often and that it will be operating just for ventilation when there is no call for heating or cooling. This can easily be 10 to 30% of the year. So if a 500 watt air handler motor operates 20% of the time just for ventilation, this will use about 876 kWh and cost the homeowner $175 a year at $.20 per kWh. Contrast that to a single upgraded bathroom exhaust fan with a DC motor that will provide the required airflow continuously using 35 kWh at a cost of $7 a year at $.20 per kWh.
Several Dedicated Supply Fans Features / Illustration
Several low-flow dedicated supply fans with filters can be installed in bedrooms or hallways. Each fan brings a portion of the required outdoor air into each room. One strategy is to bring 10 cfm into each bedroom and perhaps 20 cfm into a utility room continuously, assuming that the sum of the flows equals or exceeds the total required airflow. Care must be taken to ensure that these small supply fans provide for mixing with room air to avoid comfort issues.
Dedicated Multiport Supply Fan Features / Illustration
A multiport supply fan can be installed in a mechanical space or attic to deliver filtered outdoor air to several locations. This outdoor air can be blended with household air for tempering, but one advantage of a multiport supply fan is that is can deliver a small amount of air to several locations, reducing the potential for comfort problems from drafts.
Balanced Ventilation Systems
Balanced ventilation systems provide nominally equal amounts of supply and exhaust ventilation, so if 60 cfm of ventilation is needed, this system is designed to exhaust 60 cfm of stale indoor air and supply 60 cfm of outdoor air.
Balanced System with no Heat Recovery Features / Illustration
A supply ventilation system matched with an exhaust system of equal airflow capacity is referred to as a "balanced" system. The supply side might be an inline or through-the-wall supply fan or a central heating or cooling system's air handler. The exhaust side would be an exhaust fan of equal capacity that operates at the same time as the supply fan. The key is to match supply and exhaust flows so the dwelling unit is not pressurized or depressurized.
Heat Recovery Ventilator (HRV) Features / Illustration
An HRV moves heat between the incoming and outgoing air streams without direct contact between the incoming and exhaust air. Ventilation supply air from outside is tempered as it moves through the heat exchanger's plastic or metal core.
- In the heating season, the HRV preheats incoming ventilation air. Heat is transferred from warm, outgoing air to incoming cooler air.
- In the cooling season, the HRV pre-cools incoming air. Heat is transferred from warm, incoming air to the cooled exhaust air leaving the building.
An HRV may be a dedicated central unit that is fully ducted to or from most rooms in the house, or it may be integrated with the central air handler to use the heating or cooling ducting to distribute tempered air throughout the house. The HRV may or may not be ducted to all rooms, but the intent is to have two airstreams with approximately equal airflow to maintain a neutral pressure in the house or apartment. An HRV requires a dedicated drain for condensate.
Energy Recovery Ventilator (ERV) Features / Illustration
An ERV is similar to an HRV, but moves both heat and moisture between the ventilation supply and exhaust airstreams The ERV's core is made of treated paper or plastic to allow moisture transfer.
- In the heating season, the ERV preheats incoming ventilation air. Heat and moisture are transferred from warm, outgoing air to incoming cooler air.
- In the cooling season, the ERV pre-cools incoming air. Heat and moisture are transferred from warm, incoming air to the cooled exhaust air leaving the building.
Like HRVs, ERVs may be central fully ducted systems or integrated with the central air handler. They may be remote-mounted or inserted into the ceiling or wall. An ERV does not need a condensate drain, since moisture is transferred between incoming and outgoing air streams.
Since most California climate zones don't include hot/humid or extremely cold conditions, HRVs and ERVs operate with very similar energy efficiencies.