It is essential to circulate the air in your basement to reduce moisture, which will, in turn, retard the growth of mold and mildew. Another advantage is healthier air.
How do I circulate the air in my finished basement? To circulate the air in your finished basement, you must have a proper HVAC system and a ventilation system that addresses the specific needs of your basement. The ventilation system can either be part of the HVAC system, such as an air exchanger, or natural ventilation, a heat recovery system, an energy recovery system, or a heating and air conditioning unit.
This article will be a guide to understanding air return versus air exchange, venting, how to improve the venting that you may already have, and types of systems.
Do I Need an Air Return in the Basement?
You absolutely need an air return in the basement. What is an air return? An air return is part of the duct system in your home.
The function of the return duct is to return the circulated air to the furnace. In a house with forced air heat, return ducts are an essential part.
Return air is associated with forced air home heating systems, often referred to as Heat Pumps or HVAC systems.
Your hot air heating system needs to have return ducts on every floor, including the basement. Without the return ducts, the system will not function properly.
The return air in such systems starts to circulate from the furnace, which is usually found in the basement and moves into the supply air ducts. Every home should have a supply duct and a return duct in every room.
The exception is the kitchen and bathroom, which have separate vents that lead directly to the outside of the home.
The air returned to the furnace is cold and then warmed as it passes through the furnace to complete another cycle.
The return air ducts are under negative pressure and, therefore, should be sealed, or you risk the system sucking pollutants on its way back to the furnace for reheating.
If the return ducts are left unsealed, there will be suction on the whole house. Gases, such as radon, can be induced from the soil into the house. The air pressure in the house needs to equalize, pushing the air out of cracks and holes, minimizing efficiency (source).
The air return ducts work the same way if the air conditioner is being used rather than heat. The air leaves the HVAC and returns through the air return ducts.
Having one in every room increases the system’s ability to maintain neutral air pressure. In other words, you want the air going in and out of your system to be equal, which allows the system to work efficiently.
Typically, in a basement, ducts are installed on the ceiling. There is a problem with this setup.
If a cold air return is on the ceiling, it will take the hot air near the ceiling and return it to the furnace and vice versa for the return of hot air. The cold or hot air will not be moved up and will not circulate in the basement.
If your return air ducts are on the ceiling, moving a duct to the floor will eliminate the problem. However, do not do this in the same room as your furnace, or too close to it. You may cause a backdraft to the chimney. Place the vent where it will draw air from the next room (source).
One way to be sure your system runs at top efficiency is to keep the filters clean. Change them often, especially when you notice they are not allowing air to flow freely. Also, be sure to use the correct size filter.
Should I Ventilate My Basement?
What does it mean to vent my basement, and what will it do? Many people do not consider the basement as a separate entity separate from the rest of our home, especially if it is a finished basement. However, the basement has needs that the floors above do not.
Ventilation is simply the inside and outside air changing places. This exchange of air is of particular importance in your basement. A basement is generally humid due to being partially underground.
You may also have a storage room, perhaps a laundry room, where you keep various chemicals, old paint, and maybe even automotive supplies.
All the above, no matter how tightly sealed, eventually leak their harmful chemicals into the air. In the case of your basement, these chemicals will build up and become toxic unless you have a way to ventilate the air (source).
Another consideration of the need for ventilation is moisture. Basements are typically humid and prone to the growth of mold and mildew, both of which are harmful to your health.
Humidity will cause an unpleasant musty smell. Additionally, excess moisture also causes wood to rot.
Proper ventilation will also prevent respiratory illnesses and reduce heating costs due to not heating unnecessary water vapor.
The humidity in the air may damage the building materials you used to finish the basement, leading to the need to replace the walls, insulation, floors, and ceilings (source).
It is better to prevent problems and, in the long run, save money, and just enjoy the space you created.
There is more than one way to ventilate basements such as an air exchanger, natural ventilation, heat recovery system, energy recovery system, or heating and air conditioning unit.
How Do I Improve the Ventilation in My Basement?
A basement, especially one you have spent time and money finishing, needs some form of ventilation. In the previous section, we discussed the why of ventilation. The following sections will discuss the various systems used to ventilate basements.
If you have no ventilation in your basement at all, any of the following sections will enable you to improve the ventilation. There is always room for improvement, and each system has its benefits (source).
Natural ventilation is as simple as merely opening your windows and doors. However, for natural ventilation to work in a basement, the windows need to sit opposite one another. The opposite positioning of the windows allows the airflow to follow the natural drafts in the basement.
Older homes also breathed. Many old homes were not insulated, allowing air to flow through the building freely. As homes began to be insulated, they were still not airtight.
Air could freely flow through cracks or gaps between windows, doors, and walls. Older basements, in particular, allowed for airflow through all the cracks and spaces.
Some homes have louvered vents high up on the basement wall, which, when open, allow fresh air in and closed if it is very hot, humid, or snowing.
For many people, fresh air is always preferable but not always the most convenient. Opening and closing windows can become quite a chore. As we already mentioned, windows and doors are not the best options in the basement.
Also, if you have a wet or very humid basement, opening and closing windows will not be enough.
You will need fans or a dehumidifier in conjunction with the windows being open to control the humidity and retard the growth of mold and mildew. At this point, a mechanical system would be the better choice.
Is a Fan an Effective Way to Ventilate My Basement?
One of the simplest forms of mechanical ventilation is a fan. There are different types of fans, such as window fans, exhaust fans, ceiling fans, box fans, and all are available in various shapes and sizes.
You should keep in mind that whatever type of fan you choose must cause the exchange of indoor and outdoor air to be effective. While ceiling fans and box fans are effective at circulating the air, they will not vent stale outside air and exchange it for fresh air.
One way to use fans in a basement is to take two window fans and place them in opposite windows. Your basement may not have opposing windows so that you may look to an exhaust fan as a solution.
If your basement is of moderate size, you can put an exhaust fan on one side of the room and a ventilation fan on the other. Another option is to install an exhaust fan with a pipe ventilating the air outside (source).
Whichever method you choose to employ, ventilating your basement is imperative if you do not want mold, mildew, damage, or a funky odor.
What is an Air-to-Air Exchanger, and Do I Need One In My Basement?
First, what is an air exchanger? An air-to-air heat exchanger is a mechanical ventilation system and an important part of a home’s heating, ventilation, and air conditioning system (HVAC).
The purpose of an air-to-air exchanger is to bring outside air in and circulate it throughout the house.
An air-to-air exchange system works by taking two air streams of different temperatures, brings them into thermal contact, and transfers or exchanges the heat from the inside air leaving the house to the cold outside air coming in (source).
During the hotter seasons, when cool air is preferable, the heat exchanger will cool the outdoor air coming in.
Some, but not all, systems dehumidify the air before it circulates through the house. However, all heat exchangers take odors and other pollutants from the inside air and push them outside (source).
An air-to-air exchanger is something you should have in your finished basement. After all, you and your family will be spending a reasonable amount of time there.
Fresh air from outside will keep the inside air cleaner by filtering out pollutants from inside the home.
What Types of Air Exchangers Are In a Home?
There are a few types of air exchangers, and all move air differently through the system. The most significant advantage of having an air exchanger unit installed in the basement is the reduction in humidity.
A basement also tends to accumulate chemicals in the air as well as gasses such as radon. Having an air-to-air exchange system that introduces fresh air into the basement and draws out the polluted air is essential to your health.
Although there are more than two types of air exchangers, a house will generally use either a counter-flow air exchanger or a cross-flow air exchanger.
A counter-flow air exchanger takes two air streams — one hot, one cold — and moves them parallel to one another but going in opposite directions. A cross-flow air exchanger has the two air streams going in a perpendicular motion.
Whether you choose a cross-flow air-to-air exchanger or a counter-flow air-to-air exchanger depends solely on your needs.
Counter-flow heat exchangers are generally long and rectangular. Efficiency ratings are somewhere around 80%.
Cross-flow heat exchangers are smaller, and some can fit in a window. However, they are less efficient than the counter-flow models rating around 70%
What Are Heat Recovery Systems and Do I Need One In My Basement?
There are two types of air-to-air recovery systems: a Heat Recovery Ventilation or HRV and an Energy Recovery Ventilation or ERV. When deciding which to use in your basement, there are some questions you should ask yourself first (source).
You must first ask yourself how much fresh air do I think is enough for my home? How much fresh air already comes into my home through cracks and spaces?
What are the key differences between the HRV and ERV systems? Lastly, how do I choose between an HRV and an ERV?
The amount of fresh air in your home and how it gets in is essential. With builders constructing houses more airtight to increase energy efficiency, homeowners are facing a lack of fresh air in their homes.
Many homeowners are finishing out their basements, thus sealing the basement. Finishing the basement may increase energy efficiency but decreases the free flow of air.
The reasons you will want a mechanical ventilation system is quite simple. It is an easy way to maintain healthy indoor air.
HRV and ERV systems provide a flow of oxygen, remove contaminants, and remove excess humidity. An activity such as breathing by those living in the home contributes to the moisture.
There are standards set by the American Society of Heating, Refrigeration, and Air Conditioning Engineers for how much fresh air you need in your home.
In this, you should defer to an HVAC specialist; they have the knowledge and education to best answer this question.
Heat Recovery System
If you live in a northern or cold area, your house most likely has a Heat Recovery Ventilator (HRV). An HRV system transfers heat and reduces humidity by using the heat in the stale air leaving the house to warm the fresh air coming in.
This exchange happens in the HRV’s core. The fresh and stale air never mix but pass by each other in separate channels and exchange heat using conduction.
An HRV system uses a fan that needs to run continuously, so you will see your energy cost go up a bit.
Energy Recovery System
An Energy Recovery Ventilation System is part of the HVAC system. It exchanges the energy of stale indoor air and uses it to either warm or cool the outdoor air entering the house.
When using heat during the winter, the ERV System transfers humidity from the air outside while preheating the air on the way inside the house. This heat exchange keeps the humidity level in the home at a reasonable level.
In the summer, the opposite occurs. The ERV transfers the humidity in the outside air to the inside air going out. This process saves the homeowner money as it reduces the strain on the air conditioning system (source).
An ERV system is an efficient way to reduce your energy costs. As well as being smaller than an HRV system, the ERV is an efficient and effective way to reduce overall energy costs.
Which One Should I Choose, HRV or ERV?
When deciding which system to add to your HVAC heating and air system, you should consider the climate — is it hot and humid or cold and dry?
An HRV system is a good choice in hot and dry areas, with a moderate climate, or a marine environment.
An ERV system is a good choice in areas with the following conditions: hot and humid, cold and dry, hot and humid in summer and cold and dry in winter, a moderate climate, and a marine environment.
It is not possible to recommend one over the other. Either system is a good choice, especially if you have a finished basement. Both systems will do more to protect your investment than your HVAC system alone.
What About Fresh Air Systems for Basements?
A Fresh Air intake System (FAIS) is an addition to a home’s current heating and cooling system. It addresses the crawl space or basement explicitly.
The system pressurizes the air in the house, which effectively keeps pollutants out as it filters the fresh air coming in. The fresh air is sent directly to the air handler, which conditions the air and mixes it with the air in the house.
Effectively, most fresh air intake systems work with your HVAC system. An HVAC system is closed and does not draw air in from the outside. Therefore, if you have no other way to draw in the fresh air and let out stale air, you are merely recirculating stale, polluted air.
A FAIS works by installing a filter return grille on the outside of the house. A duct is attached to the return side of the HVAC system and the grille. The system used three filters: carbon, electrostatic, and HEPA (source).
In the previous sections, we discussed systems such as an ERV and HRV as well as vented fans. These are all examples of fresh air intake systems.
Not only do you want to circulate the air in your basement, but you also want to be sure fresh air is circulating. The circulated air will reduce or prevent the growth of mold and mildew, bacteria, chemical fumes, and gasses found in a typical basement.
To properly circulate the air in your basement, you will need more than an HVAC system. Installing a Fresh Air Intake System, an ERV System, or an HRV System is the best way to circulate the air.
At the same time, exhaust and intake fans are an option but are not as effective.
Circulating the air in your basement is imperative to having a healthy home. When you finish your basement, you expect it to be comfortable and the air to be healthy.