While many people know the role and benefits of an air exchanger in general, what type of air exchanger should you choose? HRV or ERV?

Let’s start with some definitions.

What is the difference between HRV and ERV?

They are two types of air exchangers that work differently.

The heat recovery ventilator or HRV provides this ventilation without overcooling the house. It is mandatory in new buildings (National Building Code of Canada). It has two air handling devices. The first one collects and evacuates stale air from the environment while the second one introduces outside air and distributes it throughout the house. Even better: 50 to 80% of the heat from the stale air is recovered and transferred to the fresh air entering the house! During the winter season, the HRV rejects humidity from the indoor air and some of it condenses and drips into the house drain. This is intended to dry out the indoor air, but it is possible to control the humidity level with the HRV intermittently rather than continuously.

In the summer, when the house is air-conditioned and the outside humidity is high, the HRV allows a lot of moisture to enter the house, which increases the cost of dehumidification and air conditioning.

The Energy Recovery Ventilator (ERV) like the HRV takes heat, but also takes the energy retained in the ambient humidity, greatly increasing the overall recovery efficiency. In air-conditioned buildings, when humidity is higher outside than inside, the ERV system reduces the amount of moisture that enters the home. In the winter, the ERV transfers some of the moisture in the house to the incoming air. Some of the moisture is expelled and some condenses and goes to a drain such as the HRV. This reduces dry indoor air and keeps more moisture in the air in your home.

In the summer season, some of the moisture from outside will be retained by the exhaust air and reduce the amount of moisture brought into the home. According to a recent study by the National Research Council of Canada (NRC), when the house is air-conditioned, it would save 12% on air conditioning/dehumidification compared to an HRV during the few hot and humid weeks.

In a nutshell, both systems have dual-flow fans with a core that sends heat from the stale air out to the clean air in to recover some of the heat generated by the furnace. The only difference is the nature of the core.

Desired humidity level in winter :

In fact, the humidity should be maintained between 30% and 50% in winter. The colder it is, the drier the air in your home must be to avoid condensation on the windows. Remember, however, that air that is too dry can cause lung disease or aggravate its symptoms, while air that is too humid causes other problems such as condensation and mold.

How to choose the best type of air exchanger?

 In general, you will understand that your choice between an HRV and an ERV system depends largely on the humidity level of the building. However, there are many factors that can influence the humidity level inside your home. First, there is the climate of the area. HRV is best in humid, warm climates, while ERV is favorable in cooler, drier climates. Second, there are the people living in the home. The more people in the home, the higher the humidity level. Similarly, the type of heating will have a direct impact on the humidity level of your home and therefore on the best choice to make between ERV and HRV. In a wood-heated home, which is generally drier, the ERV will help bring healthy humidity levels inside. Finally, the size of your home also influences its humidity level. In general, an HRV is better for small to medium-sized homes, because moisture can build up quickly; the ERV, on the other hand, better serves larger homes where the air tends to get drier.