In residential construction, ERVs and HRVs are the gold standards for their balanced ventilation capabilities.
By Roy Collver
An energy penalty is incurred when fresh air has to be heated or cooled much of the year; building scientists and building code developers try and walk the fine line between energy efficiency and ventilation needs.
If you want to take a real deep dive into the topic — get yourself the latest version of the ASHRAE Standard 62.1 “Ventilation for Acceptable Indoor Air Quality.” Another good source, and more accessible and relevant for most of us, is CAN/CSA-F326-M “Residential Mechanical Ventilation Systems.” Anything by the Heating, Refrigeration, and Air Conditioning Institute of Canada (HRAI) on ventilation is excellent, and of course, study your provincial building code requirements as well as those of your local jurisdiction.
Modern building codes typically use prescriptive methods to try and ensure adequate ventilation.
Structures are often classed with degrees of tightness for a variety of spaces then compared to the type of use/number of occupants to determine how much ventilation is optimal. The concept of air changes per hour (ACH) was developed to simplify code requirements for various classes of occupied space and make it easier to design ventilation systems and inspect them for compliance. Often codes will specify actual required fresh air or exhaust air on a room-by-room basis in cubic ft. per minute (CFM) or litres per second (L/s). Kitchen and bathroom exhaust fans (source control) are usually dealt with as separate items. Things get detailed with lots of charts and tables and specifics, which tells us that the code officials are taking ventilation seriously.
If you are working in residential and light commercial plumbing and HVAC in Canada, I can’t urge you strongly enough to get some detailed training and certification.
Way back when
Early ventilation systems employed a hole in the roof of a structure to let the smoke out. Next came the invention of the chimney—a slightly more elegant hole in the roof. Structures back in the day were pretty leaky and not much effort was needed to provide a pathway for fresh air to get in. When multiple rooms became more common and building methods created more airtight structures, opening windows to “get a breath of fresh air” was the high-tech solution of the day and is still a valuable indoor air quality solution. The down-side of openable windows include security and safety issues, undesirable noise, insect and air pollutant ingress, occupants forgetting to open or close them, difficulty in determining the volume of air getting in or getting out, and the difficulty of interfacing with HVAC systems—hence the ascendancy of mechanical ventilation.
There are three basic approaches to mechanical ventilation being used in our built environment today:
Pressurize—Push the fresh air in and provide pathways for the bad air to sneak out. Many apartment buildings use this approach with make-up air units pressurizing hallways in order to drive fresh air through door undercuts or transfer grilles into individual apartments. Stale air is supposed to exit via bathroom and kitchen passive exhaust ductwork, windows and exfiltration. Residentially, we have seen codes embrace the central recirculation system which pulls in the fresh air and either exhausts air from each bedroom to dump it into a common area or pulls air from a common area and dumps it into the bedrooms.
Exhaust—Push the bad air out and provide pathways for the fresh air to sneak in. This approach has been common in residential construction for years with the concept of a principal exhaust fan (often a main bathroom fan). This is interlocked with a ducted forced-air heating system, a fan that runs continually, and a fresh air intake pulling outdoor air into the return air plenum for distribution to every room. It’s challenge; how do you keep occupants from turning the exhaust fan or furnace fan off when the noise starts to get to them?
Balanced—Simultaneously push an equal amount of fresh air in and bad air out. A major issue with approaches one and two rears its head with today’s almost airtight construction methods. As a building “goes” negative or positive, the fans don’t work to specification. This seriously decreases the ventilation rate. Ducted forced exhaust interlocked with balanced make-up air, or heat recovery/energy recovery ventilators (HRV/ERV) will avoid these problems.
Balanced ventilation is the proper way to address most residential construction needs but has been held back by homebuilder lobby groups due to perceived high cost. In the original rejection of the CAN/CSA-F326, the excuse that “nobody knew how to balance these HRV things” was also given. With the average Canadian house now somewhere north of half a million dollars, perhaps it is time to finally kick the high-cost argument into the gutter.
Balanced ventilation is by far the preferred choice of most architects and engineers today for the majority of structures with some exceptions. Hydronic systems can be at a disadvantage when it comes to providing balanced ventilation as required by current prescriptive codes unless ducted air to every room through hydronic air handling equipment is part of the design.
A central forced-air heating system can utilize its existing ductwork to distribute fresh air to each room while exhausting from central points, whereas hydronic systems often need to be provided with alternate solutions. When designing hydronic radiant or baseboard/convector systems, providing separate ventilation will add cost to a project, but discreet systems can often be designed with better performance characteristics than a multi-purpose forced air heating, cooling and ventilation system for a very reasonable price.
In residential construction, HRVs and ERVs are the gold standard for balanced ventilation. Given the modest airflow rates required, the ductwork is usually small in size—making it more easily concealed in structural assemblies.
Whole house ducted systems and the recent introduction of compact “regional” and single room units are giving us more tools to work with. One of the very first residential HRV products in the Canadian market was developed by engineers based at the University of Saskatchewan, who went on to produce the VänEE HRV in the early 1980s. I installed one of their R2000 units in my house back in 1987. I have seldom lived in a house without an HRV since (retrofitted three different houses to date). Now based in Québec, VänEE still makes some of the best quality units available, but some new offerings from the Swiss company Zehnder are generating quite a buzz in the industry lately with some cool options. There are many domestic HRV/ERV product lines available these days to check out, and I believe we are going to see an increase in innovation in the sector as a result of this competition—all good news.
Given the rapid push toward net-zero house construction, my conclusion after researching this article is quite simple. As a minimum standard—ALL residential construction should utilize ducted HRV or ERV units depending on the climate. Hot-humid and cold-dry climates are best served by an ERV.
HRV units are quite good in temperate places like the West coast. Both types should be properly balanced by a technician who knows how to measure confirm airflows. As an added feature, given what we have learned during the current COVID nightmare, ventilation of any type should have the extra capacity/run at higher speeds to better remove pathogens and flush occupied spaces.
And yes—you should always be able to open a window to get a breath of fresh air when you feel like it.