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Healthy Residential Air Through Proper Ventilation
The Need for Fresh Air
As I am sure you know, modern construction practices have resulted in much tighter houses than those built a century or even just a few decades ago. As a result of homes being built tighter, indoor pollutants are trapped and have nowhere to go. Given ongoing Covid-19 concerns, many homeowners are looking for ways to keep themselves and their families safer. Healthy homes have become a top priority for both existing and prospective homeowners. Broan-NuTone® is here to help as we have many innovative ventilation products that can improve indoor air quality. Proper ventilation in homes means getting the stale air out and fresh air in. Let us investigate why providing excellent indoor air quality can be challenging.
Now that we know how new homes are built tighter and without sufficient ventilation, we can next look at some common problematic pollutants.
Code and Standard Basics
Historically, there were no specific ventilation requirements for residential buildings because there was natural leakage, and this natural ventilation or "infiltration" was considered adequate. However, as building practices have evolved and homes have become tighter, the need to ensure air quality has increased. As a result, homes must be equipped with ventilation that meets code and standard basic requirements. ASHRAE 62.2 is a residential ventilation standard that is revised every three years. It recommends requirements for both spot/local ventilation in bathrooms and kitchens and whole-home, continuous ventilation. Widely adopted building codes such as the International Residential Code (IRC), International Mechanical Code (IMC), and the International Energy Conservation Code reference most of ASHRAE's key elements. Most states adopt different versions of these model codes (IECC). Weatherization assistance programs and above-code programs such as ENERGY STAR, ENERGY STAR Indoor Air Plus, LEED, Passivhaus, WELL, and state-specific code programs also typically reference the ASHRAE standard.
Ways to Achieve Fresh Air
Spot ventilation requirements for the bathroom and kitchen are straightforward. Bathrooms require a minimum of 50 CFM delivered and kitchens 100 CFM delivered. Whole-home mechanical ventilation (WHMV) requirements are generally less well-understood. The idea is to deal with whole-home indoor air quality by continuously exhausting stale air while bringing in fresh outdoor air. The basic formula to determine the amount of air exchange needed is based on the home's square footage and the number of bedrooms. There are three different types of systems for WHMV to choose from: exhaust, supply, and balanced. In the exhaust approach, stale air is pulled out of the home with a ventilation fan. The home is somewhat depressurized, allowing fresh outdoor air to naturally make its way in through small holes in the building envelope. Generally, this approach is low cost and low maintenance. Many builders and contractors consider this a convenient way to add whole-home mechanical ventilation to a home, especially since new exhaust ventilation fans are generally quieter and more energy-efficient than traditional ones.
Exhaust Fan Features
The supply approach works oppositely. Fresh outdoor air is pushed into the home, thus pressurizing it and forcing the stale air out of small holes in the building envelope. This method is more prevalent in the southeast, with higher humidity levels. There are two basic options for deploying this approach.
Supply Fan Features
The third type of WHMV is a balanced system. This type is the most preferred for optimal indoor air quality as it combines a mechanical means to exhaust and supply air. The home is neither pressurized nor depressurized and is, therefore, the most ideal for today's tighter homes. You can achieve this by running both an exhaust fan and supply fan controlled to operate in synch; the most energy-efficient approach is to use a heat recovery ventilator (HRV) or energy-recovery ventilator (ERV). These systems mechanically exhaust stale air and introduce fresh air. Most importantly, pass the two airstreams through a core that recovers most of the temperature and/or humidity difference. This pre-temper the incoming air and minimizes losses of already heated or cooled and dehumidified indoor air.
Balanced Recovery System Features/Options
There are three different ways an HRV/ERV can be ducted. For optimal indoor air quality, a fully ducted system has special duct runs to pull stale/polluted air from bathrooms and the kitchen and special runs to deposit the fresh air into bedrooms and living areas where we spend the most time. A dedicated exhaust system utilizes these special runs only for the stale air but deposits the fresh air into existing HVAC plenums for distribution throughout the home. A simplified system uses existing HVAC ducts for both the stale and fresh air. These systems are typically the best choice for retrofit systems in existing homes.
The Need for Fresh Air
As I am sure you know, modern construction practices have resulted in much tighter houses than those built a century or even just a few decades ago. As a result of homes being built tighter, indoor pollutants are trapped and have nowhere to go. Given ongoing Covid-19 concerns, many homeowners are looking for ways to keep themselves and their families safer. Healthy homes have become a top priority for both existing and prospective homeowners. Broan-NuTone® is here to help as we have many innovative ventilation products that can improve indoor air quality. Proper ventilation in homes means getting the stale air out and fresh air in. Let us investigate why providing excellent indoor air quality can be challenging.
- More airtight insulation and weather-stripping methods
- Windows opened less often today
- Families are adding more pets
- More time spent indoors than ever before
Now that we know how new homes are built tighter and without sufficient ventilation, we can next look at some common problematic pollutants.
- PM2.5 - This stands for particulate matter 2.5 microns and smaller. This size is particularly concerning because particles of this size can pass through our nose and lungs, and bloodstream. Key sources include cooking (especially with natural gas) and outdoor sources such as traffic and wildfires.
- Excess moisture -80% of construction litigation is moisture/mold-related
- Formaldehyde from certain building materials, furniture, etc.
- VOCs from carpets, paints, cleaning and personal hygiene products, etc.
- Pet and pest pollutants
Code and Standard Basics
Historically, there were no specific ventilation requirements for residential buildings because there was natural leakage, and this natural ventilation or "infiltration" was considered adequate. However, as building practices have evolved and homes have become tighter, the need to ensure air quality has increased. As a result, homes must be equipped with ventilation that meets code and standard basic requirements. ASHRAE 62.2 is a residential ventilation standard that is revised every three years. It recommends requirements for both spot/local ventilation in bathrooms and kitchens and whole-home, continuous ventilation. Widely adopted building codes such as the International Residential Code (IRC), International Mechanical Code (IMC), and the International Energy Conservation Code reference most of ASHRAE's key elements. Most states adopt different versions of these model codes (IECC). Weatherization assistance programs and above-code programs such as ENERGY STAR, ENERGY STAR Indoor Air Plus, LEED, Passivhaus, WELL, and state-specific code programs also typically reference the ASHRAE standard.
Ways to Achieve Fresh Air
Spot ventilation requirements for the bathroom and kitchen are straightforward. Bathrooms require a minimum of 50 CFM delivered and kitchens 100 CFM delivered. Whole-home mechanical ventilation (WHMV) requirements are generally less well-understood. The idea is to deal with whole-home indoor air quality by continuously exhausting stale air while bringing in fresh outdoor air. The basic formula to determine the amount of air exchange needed is based on the home's square footage and the number of bedrooms. There are three different types of systems for WHMV to choose from: exhaust, supply, and balanced. In the exhaust approach, stale air is pulled out of the home with a ventilation fan. The home is somewhat depressurized, allowing fresh outdoor air to naturally make its way in through small holes in the building envelope. Generally, this approach is low cost and low maintenance. Many builders and contractors consider this a convenient way to add whole-home mechanical ventilation to a home, especially since new exhaust ventilation fans are generally quieter and more energy-efficient than traditional ones.Exhaust Fan Features
- Traditional ceiling mount- easy service access & variety of fan and fan/light grille styles
- Inline – takes sound downstream in duct run and features a more inconspicuous inlet
- DC/ECM Motor - energy efficient and can better overcome static pressure
The supply approach works oppositely. Fresh outdoor air is pushed into the home, thus pressurizing it and forcing the stale air out of small holes in the building envelope. This method is more prevalent in the southeast, with higher humidity levels. There are two basic options for deploying this approach.
- Central fan-integrated systems (CFIS) - A duct from a fresh air inlet on the outside of the home connects to the return air plenum with a controlled, motorized damper inline. This damper communicates with the central fan via low-voltage wiring to open whenever there is a heating/cooling call or to tell the fan to run when otherwise needed for ventilation.
- Dedicated fan - This method is similar to CFIS but relies on a small, dedicated inline fan to push the fresh air inside.
- The advantages are that it uses less energy, and the airflow is more controllable and measurable.
Supply Fan Features
- Air is coming from a known source
- Air can be filtered
- Some systems include temperature and humidity sensing of outdoor air to optimize the operation
- Dedicated fans can feature energy-efficient DC/ECM motors
The third type of WHMV is a balanced system. This type is the most preferred for optimal indoor air quality as it combines a mechanical means to exhaust and supply air. The home is neither pressurized nor depressurized and is, therefore, the most ideal for today's tighter homes. You can achieve this by running both an exhaust fan and supply fan controlled to operate in synch; the most energy-efficient approach is to use a heat recovery ventilator (HRV) or energy-recovery ventilator (ERV). These systems mechanically exhaust stale air and introduce fresh air. Most importantly, pass the two airstreams through a core that recovers most of the temperature and/or humidity difference. This pre-temper the incoming air and minimizes losses of already heated or cooled and dehumidified indoor air.Balanced Recovery System Features/Options
- Heat Recovery Ventilators (HRVs) - efficiently transfer temperature only and can be a great choice in northern climates with excess indoor humidity. An HRV is somewhat less expensive than an ERV but will require a condensate drain line.
- Energy Recovery Ventilators (ERVs) - efficiently manage both temperature and humidity and are ideal for most of the U.S., especially in more humid climates. An ERV does not require a drain line.
There are three different ways an HRV/ERV can be ducted. For optimal indoor air quality, a fully ducted system has special duct runs to pull stale/polluted air from bathrooms and the kitchen and special runs to deposit the fresh air into bedrooms and living areas where we spend the most time. A dedicated exhaust system utilizes these special runs only for the stale air but deposits the fresh air into existing HVAC plenums for distribution throughout the home. A simplified system uses existing HVAC ducts for both the stale and fresh air. These systems are typically the best choice for retrofit systems in existing homes.