What is an ERV and a HRV?
What is the difference between an ERV and a HRV?
Which is more appropriate for a Canadian climate?
Energy Recovery Ventilators (ERV) and Heat Recovery Ventilators (HRV)
By Valentine T. Gomez, P.Eng, CPHD (January 13, 2022)
Most newer homes being built today are being built more airtight, and as such require additional mechanical ventilation to bring in fresh air for the building occupants. Passive House levels of air tightness, makes mechanical ventilation an essential requirement in these high performance homes which is achieved by installing either a ERV or a HRV.
Both of these pieces of equipment are fairly new to the residential construction industry and as such the terminology is often used interchangeably, incorrectly.
An HRV (Heat Recovery Ventilator) and an ERV (Energy Recovery Ventilator) are essentially built and operate in the same way. There both have a supply air inlet/outlet and an exhaust air inlet/outlet. They are both capable of recovering heat from the building’s exhaust air and transferring that heat to fresh supply air. The supply and exhaust air pass through separate channels inside the unit’s core and heat exchange occurs through conduction. An ERV goes a step further and is also capable of recovering enthalpy (i.e. humidity).
To expand on this further;
- HRVs recover heat by using the heat in stale exhaust air to preheat incoming fresh supply air. This reduces the energy required to bring outside air up to ambient room temp and in turn saves money on your heating bills.
- ERVs recover heat and humidity, where the hear recovery process is identical to HRVs. Humidity recovery will depend on the time of year. In cold dry winter climates, an ERV transfers humidity from the stale exhaust air to the incoming fresh and dry air to help keep humidity levels at a reasonable and healthy value (40% - 60%). This reduces the load on humidifiers and saves energy. In summer, the humidity process reverses and the humidity in outside incoming air is transferred to the outgoing exhaust air. This reduces the load on existing air conditioning systems and dehumidifiers and again results in energy savings.
ERV or HRV?
It is often said the best option between the two will depend on your climate. In fact, an ERV is best recommended for all climates except hot and dry climates where humidity recovery is not a concern. The Maritimes is known for it’s hot humid summers and cold dry (air) winters, so we should be looking to install ERV’s rather than HRV’s to maximize our energy savings and help maintain occupant comfort.
An HRV will still work in the Maritimes to recover heat but will not have the added benefit of humidity recovery that an ERV provides.
If you have an HRV and want to switch to an ERV, certain manufacturer’s have removable cores which can be replaced in order to convert an HRV to an ERV or vice versa. Contact your unit’s manufacturer to find out if it this is possible.
