On the Path to a Zero Energy Home: Energy Efficient Fresh Air

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In the past, you may have heard that a home can be “too tight”… that a home needs to breathe. The issue isn’t that a home can be too tight. A home doesn’t need to breathe but people do! Over the past several years we have seen new building codes come into place that requires higher home energy efficiency. Building science has proven over many years that super insulating and super sealing a home is only part of the equation when creating an energy efficient home. While many homeowners and contractors championed these two items as the holy grail of energy efficiency, bad things happen if you stop there. The secret lies in treating your home as a system. Ventilation is one of the key systems that have to be thoughtfully designed and managed for a safe, energy efficient, and comfortable home. 

It Starts with Fresh Air  

You will hear the term ACH 50. This is a measure of how many times the Air Changes per Hour at a pressure of 50 Pascals. While it sounds technical, it is a common way to measure the “leakiness” of a home and then be able to compare it with other homes. When a home is sealed below 4 ACH 50 it means that it should be mechanically ventilated. Otherwise, the people living inside can suffer from stale air and moisture problems can arise.  

There are two common devices used to mechanically ventilate. They are designed specifically to trade fresh air for stale air and at the same time minimize the loss of energy in the process.  

Heat Recover Ventilator (HRV) – An HRV uses an exchange core to pass heat from one airstream to the other. The exchange core in an HRV can be aluminum or plastic. This core prevents indoor moisture and odors from crossing into the flow of fresh, outside air. 

Energy Recovery Ventilator (ERV) – ERVs are the same as HRVs except the core is made of coated paper or perforated plastic, which allows water vapor to pass, but keeps odors out. 


Is an ERV or HRV right for you? While they do essentially the same thing, HRV’s are used in predominantly cooler climates and ERV’s are used in predominately warmer climates. It would be easy to decide which is best for you if the country were simply divided into the northern part and the southern part. However, the U.S. has eight climate zones. It is best to enlist the services of a qualified Heating, Ventilation, and Air Conditioning (HVAC) expert when deciding which one and what size is best for your situation. 

Manage the Moisture 

In the old days when houses were leaky and windows were built poorly, a home was very energy inefficient but ventilation occurred freely and moisture was easily able to escape from a home. With today’s building codes and much better windows, it is easy to get moisture trapped in a home. Hot showers with no ventilation fan on, cooking, water leaks and condensation can cause the excessive buildup of moisture in homes today. This moisture gets created and has no way to escape, or dry, from the home. Trapped, excessive moisture is one of the key ingredients for mold growth. 

The goal is to maintain an indoor relative humidity between 30% and 50%. Most climates will benefit from removing small amounts of indoor water vapor with an HRV. In dry climates, the home will benefit from an ERV that retains some water vapor in the living area. In warm humid climates, ERVs help keeps excessive humidity outside. Just moving the air regularly with either type of ventilation system will help prevent mold and keep indoor air pleasant. Good moisture management requires that water vapor stays outside in humid climates or inside in dry climates. 

What about My Fuel Burning Appliances? 

Not all homes have a natural gas stove, an oil furnace, or an LP gas water heater. But if you do, it is important to isolate the ventilation sources for these appliances. Isolate them from both a health and safety perspective and an energy efficiency perspective.   


Atmospheric combustion appliances use air from the space around them for combustion. If you are going to have combustion appliances the best approach gives them their own living space. This means you can air seal and insulate the room where they will live from the rest of the living space of the home. Once you have done this you can give them their own air supply and separate ventilation. This helps eliminate the issue of a very tight house sucking carbon monoxide back down an exhaust flue when a bathroom fan, a clothes dryer or a range hood are turned on elsewhere in the home. 

We Have Only Scratched the Surface 

When it comes to managing fresh air and moisture in your home, there many options, approaches, and techniques. Key areas where air enters or leaves the home are bathroom exhaust fans, range hoods, and clothes dryers. The normal closing and opening of doors has a minimal impact under normal use. However, the big items can have significant impacts on home ventilation.  

Moisture management is another area that bears further understanding and research when designing and building a new home. Excessive moisture needs to escape. Hot showers and cooking are two main culprits creating excessive/trapped moisture in today’s home. Learn how simple habits can reduce moisture and the corresponding potential for mold growth. 

Modular Homes have Energy Efficiency Built In 

Modular homes can be much more energy efficient than their site built counterparts. Modular construction is a building system. By using a consistent system to build your home, details that are often overlooked in traditional construction are managed and done properly in a factory environment. Building a home to a high performance standard is almost a by-product of building indoors.   

Because today’s modular home can be so energy efficient, it is important to evaluate your home ventilation options. Don’t just stop halfway. Today’s home is comprised of many systems. When the thermal envelope is tight and sealed it depends on the HVAC system to provide safety, comfort, and protection to its occupants. Modular takes home construction to the next level. Modular means more!

About the Author
Ken Semler

Ken Semler

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Hi, I am Ken Semler the founder of Impresa Modular. I am passionate about our company and the homes that we provide. Modern modular construction enables us to deliver healthy, safe, and energy-efficient living spaces. Impresa Modular is a licensed/registered/certified builder/contractor in almost every state. I believe that modular homes provide the best way to deliver virtually unlimited design flexibility at the greatest value.

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  1. Jean DeRosa

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