July 9, 2025
In the past, ventilation systems weren’t really necessary due to the way that homes were built and the materials that were used. Most older homes have plenty of passive ventilation due to their exterior structure not being very airtight. You’ll sometimes hear people talk about how old houses can breathe, as they have gaps in their exterior envelope that result in air continually flowing in and out.
Advances in building practices and the development of better building materials have resulted in homes continually becoming tighter, meaning there are few, if any, gaps in the envelope. Having a well-sealed envelope is important for ensuring that the house is as energy efficient as possible and costs less to cool and heat. However, it also comes at a cost since it prevents the house from having any passive ventilation.
This is where installing a balanced ventilation system can be extremely beneficial. In this article, we’ll discuss the reasons ventilation is important for your home as well as how balanced ventilation works and what types of systems are available.
The Role Ventilation Plays in Indoor Air Quality and Comfort
Insufficient ventilation can create significant issues in terms of indoor air quality and humidity control. Without adequate ventilation, the air inside a house tends to be overly stale and smelly. There are also many different sources of airborne pollution in a house, and their concentration is always much higher if there isn’t sufficient ventilation.
In places like St. Louis, homes that aren’t well ventilated also tend to be much more humid during the summer months. The air in our area is almost always fairly humid during the summer, and everyone in a house contributes to indoor air continually becoming even more humid due to the moisture evaporating off their bodies as they sweat. High humidity is a concern because it makes the house feel hotter and less comfortable. It also makes the air conditioning system work less efficiently, resulting in higher electricity bills.
Mechanical ventilation systems help prevent or at least lessen all of these issues. The system is usually on a timer and will run every so often to pull the stale, humid air out of the house and bring fresher, cleaner air in from outside. You can also exchange or replace the stale air in your home with fresh air just by opening windows on different sides of the house to create a through-draft. However, this is obviously not something you want to do during the summer in our area since you’ll just let lots of hot, humid air inside, making your house much less comfortable and forcing your AC to work overtime.
Types of Ventilation
In addition to passive ventilation, there are three different types of mechanical ventilation: exhaust ventilation, supply ventilation and balanced ventilation. Exhaust ventilation just involves using a fan to draw air out, and common examples of this are the exhaust vents in kitchens and bathrooms. Supply ventilation involves using a fan to pull in fresh air and force it into the building. Both exhaust and supply ventilation systems can create significant issues by causing the pressure in the building to be much higher or lower than it should be. This is where balanced ventilation systems are superior, as they provide both supply and exhaust ventilation at the same time to maintain equal air pressure.
Types of Balanced Ventilation Systems
The two primary types of ventilation systems are heat recovery ventilators (HRVs) and energy recovery ventilators (ERVs). Both systems are designed to provide balanced ventilation without negatively impacting the temperature in the house and decreasing your home comfort.
The systems consist of two fans and a core that contains some type of heat exchanger. One fan is the exhaust fan that pulls air out of the house and blows it outside. The clean-air intake fan spins in the opposite direction to pull outdoor air into the house. Although the two air streams never mix, they do essentially cross paths as they flow through the core.
During the summer when the incoming air is hotter than the outgoing air, the heat exchanger in the core absorbs much of the heat the incoming air contains. It then transfers this heat to the outgoing air. The result is that the incoming air gets cooled to where it’s about the same temperature as what it currently is in the house. This process is vital for ensuring that the ventilation system doesn’t just continually pull in hot air and quickly cause the indoor temperature to increase.
This same heat transfer process works during the winter as well, just in the opposite direction. That means the heat exchanger uses the heat in the outgoing air to raise the temperature of the incoming air. This is equally important, as the incoming air basically gets pre-heated to prevent the heating system from having to do extra work.
The difference between the two types of systems is that an HRV can only transfer heat, whereas an ERV can also capture and transfer some moisture or humidity. HRVs work just fine and don’t create any issues in places with dry summer weather. However, running an HRV during the St. Louis summer would quickly lead to the humidity level in the house being far too high and potentially create issues with mold growth. An ERV, on the other hand, will pull humid air outside of the house while also decreasing the humidity level of the air it brings inside. In many cases, this eliminates the need for any other type of dehumidification and makes it the superior option for humid climates.
Benefits of an ERV in Winter
Dry indoor air is a common problem during the winter, which occurs for two separate but related reasons. To understand these reasons, it’s necessary to know the difference between absolute humidity and relative humidity. Absolute humidity measures the total amount of moisture in the air as a percentage of how much moisture the air is capable of holding. Relative humidity is just how moist we perceive the air to be.
As long as no moisture is added to or removed from the air, absolute humidity remains constant. However, relative humidity continually decreases as the air temperature increases and vice versa. That’s because the hotter the air is, the further apart the molecules are. That means there is more space for the air to hold additional water molecules. We don’t perceive the air to be as humid (lower relative humidity) when the air is hotter and the absolute humidity is lower, as the water molecules are more spread out and fewer of them come into contact with our bodies.
When the air is colder, the molecules are much closer together. That means the air can’t hold nearly as much moisture, which is the first reason why winter air tends to be fairly dry. When you run your heating system and raise the temperature of the air, it makes the air feel even drier. The actual moisture content or absolute humidity stays the same, but the relative humidity drops and makes you perceive the air to be drier.
If you had an HRV, it would just make your house even drier during the winter by continually pulling moister air outside and bringing drier air inside. That means it would cause the absolute humidity in the house to decrease along with the relative humidity. An ERV will instead capture moisture from the outgoing air and use it to humidify the incoming air. The result is that your house won’t feel nearly as dry as it normally would.
Improve Your Comfort Today
For the best home comfort and indoor air quality solutions in St. Louis, look to Scott-Lee Heating Company. We install ERVs and a range of other indoor air quality equipment, and our expert team can help you find the right option for your home. For more information, contact us today.