A Look at HRV's and ERV's

​I owe a lot of my skill as a home inspector to the time I spent working at NSCC (Nova Scotia Community College), where I was not only able to access high quality training but was able to see firsthand how complex modern technology helps to create safe, healthy, efficient buildings. NSCC is a leader in sustainable building practices, and I have taken plenty of courses on topics such as Heating, Air Conditioning, Pipe and Air System Design to name a few. I also learned to apply many of these principles to my own home and one project I will be working on soon is to look at replacing our HRV, possibly with a modern ERV. Modern building codes require the installation of mechanical ventilation (i.e. just exhaust fans are no longer acceptable) as modern homes are built very tight for energy saving purposes. 

What is an HRV? ERV?
HRV stands for Heat Recovery Ventilator while ERV stands for Energy Recovery Ventilator. These two systems are very similar with the difference being that an ERV recovers both heat AND moisture. Personally, I think they should be called HMRVs (Heat & Moisture Recovery Ventilators) as this would be a better descriptor. Here is a basic diagram about how these systems work. While it appears the air mixes based on this picture, they remain completely separate with only heat (and possibly moisture) being exchanged.

So, Does This Mean a ERV is Better?
Not necessarily. While ERVs are considered a step above HRVs (and more expensive!) opinions vary on which is the right choice in Nova Scotia. While we do have humid summers, having too much humidity is not an issue for the rest of the year and heating is prioritized over cooling in our province. When considering installing a new unit, remember mechanical ventilation is a job that should be left for a qualified HVAC contractor and they can offer the best advice on what will be effective for your situation.

How Are These Units Different from an Air Exchanger?
An air exchanger does exactly what it says: exchanges air from inside to outside and replaces it with outside to inside air. This works great in theory but in reality it is rare that outside conditions are as comfortable as the ideal indoor conditions. The air outside is typically colder and bringing in constant fresh air without capturing heat from the air vented outside will lead to unnecessarily high energy bills. In short, a HRV is a step above an air exchanger with an ERV being another step above that. 

HRVs and ERVs Need Maintenance Too! 
While they are generally very reliable and are designed (and supposed) to run 24 hours a day for 20+ years, they still require regular maintenance just like any piece of HVAC equipment. The biggest faux pas (other than a home missing an HRV/ERV entirely) I see is units that have not been cleaned (often times it is clear they have NEVER been cleaned!). It is important to inspect for proper operation and clean the unit according to manufacturer's instructions, typically once a season. Are these units pricey? Absolutely, but it is a small price to pay for a clean and healthy home!