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Heat and Energy Recovery Ventilators (HRV and ERVs)
By Mike Holmes
Tuesday, July 13th, 2021 @ 1:19pm
I’ve been talking about the importance of good indoor air quality for years. If your home can’t properly get rid of excess humidity, it can get inside your walls and lead to problems with mold and rot in your building materials.
My number one way for properly creating that efficient air exchange is by installing a heat recovery ventilator, or even better, an energy recovery ventilator.
Air Exchange Systems
If you have an efficient air exchange in your home, which will cycle in fresh outdoor air, you can pull out the moisture filled air.
There are two types of mechanical ventilation systems to consider: heat-recovery ventilators (HRV system) and energy-recovery ventilators (ERV system).
Simply put, an HRV and ERV will supply fresh indoor air to homes, while reducing heating and cooling costs (energy efficiency). So what’s the difference between an ERV and an HRV?
What is a Heat Recovery Ventilator?
A HRV system supplies continuous fresh air from outside in the house.
Your Heat Recovery Ventilator (HRV) will either be connected to your existing forced-air heating system, or a specially installed network of outdoor air ducts. It will feature two fans – one that expels the indoor air from your home to the outdoors, and other one that brings fresh outdoor air into your home.
Before that fresh air is distributed throughout your home, it will pass through a heat exchange core, that transfers heat from the outgoing stream of air to the incoming stream. This creates an efficient heat exchange that reduces the energy necessary to warm the replacement air to a comfortable temperature.
Some builders choose to install HRVs in their homes.
The Benefits of an HRV
When it’s running well, your HRV can recover up to 80 percent of the heat from the outgoing – which can go a long way to reducing your ventilation and space heating costs. Now that’s smart.
HRVs can remove stuffy air from rooms with limited air flow, like basements, laundry rooms, and bathrooms. They also drive fresh air into more frequently used rooms like bedrooms and living rooms to maximize comfort.
Photo of a HRV from Holmes Approved Homes builder RDC Fine Homes.
Some HRVs have a humidistat which should be installed in a central spot in the house.
TIP: Pay Attention to Building Code Requirements
An HRV is required depending on the insulation values. As an example, Edmonton is in Climate Zone 7A. Code specifies that no HRV is required if the effective insulation is above R60 attic, R17.5 walls, and R20 below-grade basement walls. An HRV is required for insulation levels between R50-R60 attic, R17-R18 walls, and R16-R20 basement walls.
If the radon levels in the home exceeds 200 Bq/m3, a Radon Mitigation Fan is required. Often an HRV will provide enough ventilation to bring excessive levels back down to the safe threshold. Where there is no HRV, the Mitigation Fan is needed.
What is an Energy Recovery Ventilator?
Taking things a step further than your HRV brings us to Energy Recovery Ventilators (ERVs). ERVs also have the ability to manage the moisture in the air that’s being pulled into your home. This means that in the winter, your ERV will transfer humidity from the air being extracted from your house, keeping your humidity levels relatively stable.
During the hot summer months, the opposite happens, where moisture is pulled out from the incoming air – which reduces the work your air conditioner and dehumidifier have to do to keep things even.
The Benefits of an ERV
ERVs are a great fresh air solution to our cold Canadian winters since the air coming from the outside can be very dry, messing with the humidity levels in our homes. When humidity falls severely, you may notice some shrinkage or warping of hardwood surfaces. Low humidity can even have an effect on your personal health, with low humidity levels causing dry, itchy skin, or cause feelings of congestion.
In the summer, an ERV system can reduce humidity in your home, which helps prevent mold growth and keeps air feeling fresher.
HRV Vs ERV. Which One To Choose?
Remember that an HRV system will exchange heat and an ERV will exchange heat and moisture.
If the area you are in an area that experiences extreme weather (humid summers and dry winters), look into an ERV.
If you have a large family that cooks a lot, an ERV will take care of the moisture generated from the kitchen.
ERV’s are best suited for moderate winter locations. In locations with colder winters ERVs CAN freeze up. An HRV has a “defrost cycle” which prevents ice build-up in the heat exchange core. Although there are many benefits for ERV use (due to its ability to humidify), you must be careful to use them in appropriate locations.
What If I Don’t Have an ERV or HRV?
If you aren’t able to upgrade your systems to include an HRV just yet – there’s still something you can do to promote air exchange. It’s pretty simple, just open your windows for a couple of minutes a day and let some fresh air flow in. It won’t provide the same efficient heat energy exchange that you’ll get with an HRV, but it can still help you deal with minor condensation. This can alter your humidity levels, so I hope your humidifiers and dehumidifiers are up to the task.