The three main whole-home mechanical ventilation strategies are exhaust-only, supply-only and balanced.
Balanced systems may include heat recovery (HRV) or heat and moisture recovery (ERV). Balanced airflow and energy recovery are different features.
The right choice depends on climate, indoor humidity, existing ducts, outdoor air quality and combustion appliances. There is no single best system for every home.
Whole-home ventilation works alongside natural ventilation and local kitchen or bathroom exhaust. Spot exhaust is itself a form of mechanical ventilation.
Use this guide to compare the strategies before discussing the ventilation needs and practical installation options for your home with a qualified contractor.
PNNL’s guide to existing-home ventilation explains why the system should be chosen and installed for the conditions in your home.
Why Is Ventilation Important?
At its simplest, ventilation is purely the exchange of indoor and outdoor air.
Exchanging fresh new air and stale old air is a seemingly easy process. But there are multiple ways to ventilate an indoor space and a couple of different mechanical home ventilation systems to choose from that aid the process.
Ventilation is necessary because, without the new-old air exchange, harmful indoor air pollutants are stuck circulating inside. And what’s stuck circulating inside, you and your family are stuck breathing. There is a multitude of factors that affect indoor air quality. Things like excessive moisture, poor humidity regulation, pets in the home, gases from cooking and all sorts of factors worsen air quality. They’re also the factors that make ventilation even more critical.
It’s All About Your Health
- Dilute indoor pollutants: Ventilation can lower some indoor pollutant levels. Consider outdoor air quality when deciding how to ventilate.
- Address pollutant sources: Ventilation does not eliminate all allergens. Reduce sources of pollution and consider suitable filtration.
- Manage moisture: Ventilation can help remove moisture, but it does not fix leaks. Repair water problems and control humidity to help prevent mold.
A Comfortable & Fresh Home
- Account for outdoor conditions: Incoming outdoor air may need heating, cooling or dehumidification. Ventilation does not automatically reduce air-conditioning use.
- Control pollutant sources: Kitchen and bathroom fans that exhaust outdoors remove pollutants near their source. Whole-home ventilation does not replace source control.
- Plan for comfort: Outdoor temperature, humidity and system design affect comfort. Some homes need additional dehumidification.
Protect Your Investment
- Address water problems: Repair leaks and manage indoor humidity. Ventilation is one part of moisture control and does not fix water intrusion.
- Maintain the system: Follow the manufacturer’s maintenance instructions for fans and filters, and keep outdoor air openings free of debris.
Ventilation is particularly important today as modern building standards and construction codes have resulted in more airtight homes and buildings.
Air can enter a home through cracks and gaps in walls, floors and ceilings and around windows and doors. This air leakage is called infiltration.
Mechanical ventilation uses fans to exhaust indoor air or supply outdoor air. Options range from a kitchen or bathroom exhaust fan to a whole-home system that distributes outdoor air through ducts.
Three Types of Ventilation
To understand the whole-home mechanical ventilation options, you first need a better understanding of how ventilation is at work in your home already.
Natural Ventilation
Natural ventilation brings outdoor air indoors through open windows and doors without fans. The EPA distinguishes this from infiltration through cracks and gaps.
Wind and indoor-outdoor temperature differences drive natural airflow. Open windows only when it is safe and outdoor air quality and weather permit. Avoid opening them when pollution or pollen is high or during extreme temperatures or humidity.
The age or draftiness of a home does not by itself establish adequate ventilation. Assess existing ventilation, indoor pollutant sources and measured airflow before deciding whether to add a mechanical system.
Spot Ventilation
Spot ventilation is the use of localized exhaust fans. It is a form of mechanical ventilation. Spot ventilation uses fans to exchange air, but it is localized to a specific area of the home only. Think kitchen or bath fans, for example.
These extremely concentrated ventilation systems aim to remove pollutants and odors (like those caused by cooking) or remove excess moisture from a space (as caused by a shower). These localized systems used to be the extent of mechanical ventilation in homes.
Whole-Home Ventilation
Now, mechanical ventilation systems have evolved into whole-home ventilation systems. A whole-home or whole-building system uses one or multiple fans and ductwork to effectively bring fresh outdoor air indoors and remove stale indoor air.
The goal of a home ventilation system is to both improve indoor air quality and effectively ventilate a large space.
Whole-home ventilation can help dilute pollutants from indoor sources. Its effectiveness depends on the amount of outdoor air supplied and the quality of that air. Consider nearby smoke and other outdoor pollution when choosing how to ventilate.
Some systems can use suitable existing HVAC ducts; others need separate ductwork. Have a qualified contractor assess duct leakage, air distribution and controls before integrating ventilation with the heating or cooling system.
Filtration depends on the intake location and equipment. In a central fan-integrated supply system, outdoor air entering downstream of the filter at the air handler needs a separate filter. Reusing HVAC ducts alone does not ensure that incoming air is filtered.
Three Types of Whole-Home Mechanical Ventilation Systems
Home ventilation is one part of improving indoor air quality. Reducing or removing indoor pollutant sources is usually the most effective first step. Compare the systems below with the needs of your home and outdoor conditions in mind.
Exhaust-Only
Exhaust-only ventilation removes indoor air outdoors. Replacement air enters through leaks or passive inlet vents. A suitable bathroom fan can provide whole-home ventilation when airflow is verified and controls provide continuous or scheduled operation. Installation can be relatively inexpensive when existing fans and ducts are suitable.
Exhaust-only ventilation causes depressurization. Replacement air can be difficult to control and can add moisture in humid climates. These systems do not recover heat. Incoming air may need heating, cooling or dehumidification; costs depend on climate, airflow and equipment.
Exhaust-only systems can draw pollutants through leaks or from neighboring units with shared walls. Have a qualified contractor assess natural-draft combustion appliances for backdrafting. Suitability depends on the home.
Supply-Only
Supply-only ventilation uses a fan to bring outdoor air through a designed intake. Locate the intake away from exhaust outlets and other pollution sources, not in an attic, garage, basement or crawlspace. Incoming air can be filtered when suitable filtration is installed and maintained. Keep intake grilles clear of debris.
Supply-only ventilation pressurizes the home, pushing indoor air out through leaks and vents. In cold weather, moist indoor air can condense in colder building assemblies. Basic supply systems do not recover heat or actively remove moisture; incoming air may need heating, cooling or dehumidification.
A supply system can use suitable central HVAC ducts to distribute outdoor air throughout the home. Have a qualified HVAC contractor check duct leakage and controls and verify outdoor airflow. Fan electricity and energy used to condition incoming air affect operating costs.
Balanced
A balanced system supplies and exhausts air at similar rates. Suitability depends on ventilation needs, climate and installation conditions. No one strategy is best for every home.
Balanced systems exhaust stale polluted indoor air and supply outdoor air. Wind, other exhaust fans and poor balancing can still affect house pressure. Have a trained HVAC technician assess natural-draft combustion appliances.
Installation costs depend on equipment and ductwork. Compare fan electricity, heating and cooling loads, and maintenance. An HRV or ERV can reduce conditioning loads, but savings depend on climate and equipment. In mild climates, fan electricity can cost more than the recovered energy saves.
Some balanced systems use an HRV or ERV to recover heat or moisture. Others coordinate supply and exhaust fans without recovery. Balanced airflow and energy recovery are separate features.
Heat Recovery Ventilator
A heat recovery ventilation system (HRV) transfers heat, rather than moisture, between outgoing and incoming air. It can recover heat in winter and reduce incoming heat in summer. The HRV-versus-ERV choice depends on year-round humidity, climate and the home, not cold weather alone.
Energy Recovery Ventilator
An energy recovery ventilation system (ERV) transfers heat and moisture. In hot, humid weather with cooler, drier indoor air, it can reduce incoming heat and moisture loads. It does not replace air conditioning or dehumidification. In cold weather, moisture retention may help or worsen indoor humidity. Choose for year-round conditions.
Upgrading to a Balanced Whole-Home Ventilation System
Before choosing an HRV or ERV, ask a qualified contractor to assess ventilation needs, indoor humidity, local climate and existing HVAC equipment. The right system and installation depend on conditions in your home.
