We recently wrote a piece about the importance of an airtight home. The core premise is that a structure that allows for air transport – one that is not airtight – defeats the purpose of any measures taken to keep it warm in winter and cool in summer. Sensible enough. But an airtight home also needs to manage for indoor air quality. As a friend of ours recently commented.. “while buildings do not need to breathe — the occupants do”. So how should an airtight home also allow for, and create fresh, clean air for its occupants? Let’s keep it high level and address the basic concepts and solutions.
Get Fresh Air into Your Home…. Efficiently
Back in the old days of leaky homes with drafts, you didn’t worry about air exchange. It happened 24/7. The result was a home that breathed but in an incredibly inefficient way. Fast forward to today’s efficient homes and this air exchange process should be accomplished by Mechanical Ventilation Systems. These systems can help replace oxygen in the home, remove toxins and chemicals and keep humidity at appropriate levels.
Two Basic Ventilation Systems
A Heat Recovery Ventilation system (HRV) takes the heat from air leaving your home (kitchen, bathroom exhaust) and mixes it with incoming fresh air. So you get the benefits of fresh air without having to heat it back up completely to ambient temperatures. As with most machines, the efficiency can vary with HRV’s but the basic setup is the same. Two ventilation ducts run into an exchanger where outgoing air can pass along its heat to incoming air.
An Energy Recovery Ventilation (ERV) system functions similarly to an HRV but goes a step further and balances humidity levels as air gets exchanged. In colder months, the ERV takes the moisture from the outgoing indoor air and mixes with the incoming colder air. When seasons change, the system will reverse and remove excess humidity from incoming air. As we’ve written about before, moisture management in any home is key, especially the airtight ones so an ERV system can make a significant difference.
The choice between an HRV and ERV will depend on where your house is located, the humidity level in your home, the size of your family, and personal needs. A large home with few occupants in a generally drier climate may not require the humidity management of an ERV while the opposite (small house, lots of people, humid area) may need more than just the heat recovery of an ERV.
Any discussion about mechanical ventilation systems and indoor air quality should also include whole-house dehumidifiers. Indeed, drier air tends to be healthier air as it limits fungal and microbial levels. HRVs and ERVs will seriously improve IAQ but they are not designed specifically to remove moisture from the home. So if this is a concern (and you have the budget!) you should consider adding a dehumidifier for the purposes of managing moisture of your indoor air. Let the ERV or HRV produce fresh air.
Your Building Envelope Matters
Every house, even the most efficient, leaks some air and a fair amount of that is directly through the overall wall system. So it is crucial to pay attention to what is in your walls as that construction can either help or hurt your indoor air quality. Think of it as an air filter. Here is where Havelock Wool comes in as not only high-performance insulation, as measured by R-Value and its ability to manage moisture, but also as a source of passive air filtration. Wool has the unique ability to irreversibly bond which chemicals such as formaldehyde, NOx, and SO2. So when toxins develop or are introduced into your living space the natural filtration aspect of wool insulation kicks in. Of course, this characteristic needs to be considered relative to where the primary air barrier is placed which is why we might advocate for placing it on the exterior of the wall cavity. And finally, given it is a completely natural product wool insulation does not introduce toxicity into your wall system.
Don’t needlessly introduce chemicals into your home
Seems straightforward enough but VOCs and chemicals routinely find their way into homes or are created inside. Furniture is one such culprit as it often contains formaldehyde (via pressed-wood products like particle board) as well as glues and adhesives. Check The Red List for a list of the bad stuff and where you can avoid these materials in your home’s furniture.
Further, chemicals routinely find their way into the home via cleaning agents. A TON has been written about improving IAQ by using non-toxic cleaners, etc so we won’t try to add more here other than to say it’s worth being mindful of the impact that common household cleaners have on indoor air quality.
And lastly, CO, CO2, and VOCs are created when frying or grilling toasted foods so whilst you can certainly limit exposure it is difficult to nullify it entirely. As such, material selection along with high-quality ventilation is of extreme importance in today’s built environment. Be vigilant, don’t take anyone’s word for it, and get what you want when you build or remodel!!
Dave Rohner DCR Services
Thanks for the blog
I have been saying this almost as long as Matt Risinger
Unfortunately there is not enough education on this subject as it is not required by most “codes”
But it’s extremely important the average person understands that building science and technology allows us to build for long term, like they have for 100s of years.