An HRV is a heat recovery ventilator and can be used in both the heating and
An HRV is a sensible-only recovery device. That means it can recover
sensible (dry) energy but not latent (moisture) energy. This does make it
less effective during the cooling season.
An ERV system is a sensible-plus-latent device. ERV systems provide a
controlled way of ventilating a home while minimizing energy loss.
Both HRV's and ERV's include a heat exchanger, one or more fans to push air through
the exchanger, some controls and are typically central, whole house
ventilation systems with their own duct system or shared ductwork.
Although both HRV's and ERV's capture thermal energy, ERV's transfer a high
percentage of the water vapour to the air stream with the least amount of
moisture. That means an ERV "kicks out" some of the incoming moisture in
summer, keeping your home more comfortable, and retains some humidity in
winter, again providing more comfort.
Excessive moisture should be considered a pollutant!
Most energy recovery ventilation systems can recover about 70% to 80% of the
energy in the exiting air and deliver that energy to the incoming air.
However, they are most cost effective in climates with extreme winters or
summers, and where fuel costs are high.
In the summer, an ERV removes the humidity from the incoming outdoor air and
shifts it over to the exhaust air, keeping it out of the building, the
inside air also cools the warmer supply air to reduce ventilation cooling
In the winter, an ERV removes humidity from the exhaust air and transfers it
over to the outdoor ventilation air, eliminating the need for humidifiers,
it also reduces the costs of heating ventilated air by transferring heat
from the warm inside air being exhausted to the fresh (but cold) supply air.
The graphics above illustrate the impact an ERV has on the temperature of a
building's airflow in winter and summer conditions. The DB (dry bulb)
measurement indicates the pure air temperature. The WB (wet bulb)
measurement indicates the temperature in relation to the humidity level.
Moisture always moves from the air stream that is the most humid to the
one that is the driest.
There are essentially four different types of ERV's.
The decision to use an ERV (a sensible-plus-latent device) or an HRV (a
sensible-only device) is a matter of psychometrics.
The general guideline for applications for most climate zones is to always
use an ERV to get the greatest energy benefit, as well as greatly improve
Because ERV's generally cost more than HRV's, the latter are used more often.
For ERV systems simplicity is key to a cost-effective installation. To save
on installation costs, many systems share existing ductwork. Ensure the
installing HVAC contractor has enough technical expertise and experience to
install an ERV. In general, you want to have a supply and return duct for
each bedroom and for each common living area. Duct runs should be as short
and straight as possible. The correct size duct is necessary to minimize
pressure drops in the system and thus improve performance. Insulate ducts
located in unheated spaces, and seal all joints.
There are applications where an HRV makes more sense, such as a
locker/shower room. In this case, the indoor humidity always is much higher
than the outdoor humidity and it is desirable to remove that moisture from
the space at all times of the year.