Building Blog #1 - What’s the deal with ERVs? / by Michael Mazurkiewicz

Written by: Donald Peckover

 

Question: What is an ERV (or HRV) and why do I need one?

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Answer:
An ERV is an Energy Recovery Ventilator. Its little brother is an HRV, or Heat Recovery Ventilator. Either is needed when building a new, energy-efficient, airtight home (or renovating your current home) to ensure that you have fresh indoor air without unnecessarily losing heat through your building envelope (your walls, roofs, floors; and around windows and doors). An ERV has the capacity to hold onto or repel humidity as well as heat, depending upon the season. An HRV only handles heat, and for this reason (and further explained below) we recommend an ERV as opposed to an HRV.

Gaps around windows and at mortar joints (left) can lead to air infiltration and further indoor problems (right)

Gaps around windows and at mortar joints (left) can lead to air infiltration and further indoor problems (right)

Hundreds of years ago – and even only decades ago as well - homes relied on gaps in the building envelope to provide fresh air into the home. These homes were not airtight and we were regularly losing warmth in the winter through the building envelope. Drafty windows also lead to problems with mould, condensation, and even ice build-up in the winter – things we want to avoid too! With the move towards sustainability and green building we aim to seal up all these gaps, and in doing so we need another method to introduce fresh air into the home. Here enters the ERV.

The inner workings of an ERV

The inner workings of an ERV

I always say that an ERV is a magic box, and it really is. Inside the outer casing is an air handler and heat/humidity exchanger core. What the air handler does in winter is draw fresh, cool, dry air from outside while also drawing stale, warm, moist air from the inside of the home – usually from bathrooms, kitchens, and hallways. Inside this exchanger core is where the magic happens: warmth and humidity is transferred from the outgoing stale air into the incoming fresh air via a process of magic, but is really a simple process of diffusion and heat transfer. In this process we expel the stale air but do not lose that heat and humidity, which is nice to keep in the house in the dry wintertime as much as possible. The process also avoids throwing all that heat directly outside, improving the energy efficiency of your home especially when coupled with your high-efficiency heating system.

A mechanical room with forced-air furnace (left), ERV (top), and greywater system (right). Stay tuned for more info on greywater!

A mechanical room with forced-air furnace (left), ERV (top), and greywater system (right). Stay tuned for more info on greywater!

An ERV is also helpful in the summertime as well. The same laws of physics described above keep the warmth and humidity of the outside air outside, while still bringing in fresh, oxygenated air. Through this process of indoor humidity control we can lower the perceived temperature inside. It’s like removing the Humidex factor from the weather report – you actually only feel the air temperature and not the humidity. Therefore we make the home feel more comfortable without the need for extensive air conditioning… and if you are OK with a few muggy nights in August we can get rid of the air conditioning system altogether, saving you upfront construction costs and long-term energy and maintenance costs.

With the growing trend towards sustainability and the demand for green building the Ontario Building Code now requires an ERV in all new homes and major renovations. Most importantly, though, ERVs deliver fresh air throughout the home during the entire year, making your indoor spaces comfortable and healthy, along with the added benefits of energy efficiency. What’s not to love?