The Crazy Truth About Ventilating Your House
All homes need ventilation, but most people don't know how much or what kind.
Should you open the window? You can, but it's probably not practical during peak summer or the dead of winter. It might be too hot or too cold outside. And besides, you don't want conditioned air to escape from your home.
What about bath and kitchen fans? They definitely get humid or stinky air out of your home, but they also force unfiltered air into your home through gaps and cracks in the building envelope. Every time you run an exhaust fan, air enters your home to relieve the pressure balance. You could be bringing in soil gases, industrial pollutants, or humidity. Ugh. Not good.
So, what's the right ventilation option for your home? The "crazy truth" depends on how "tight" or "leaky" your home is - and how much you value indoor air quality.
In the old days, nobody had to think about ventilation
If you've ever lived in an old house, you understand the meaning of "drafty." Before the days of batt insulation and caulk tubes, nobody needed to think about ventilation - their homes ventilated themselves.
During the summer, there wasn't any air conditioning. People just opened the windows, fanned themselves, and tolerated the humidity. During the winter they burned wood. Or coal. And they burned a lot of it. Air infiltration was off the charts in these homes!
Things are different nowadays. We use building materials that prevent significant exchanges of air, keeping conditioned air inside for relatively long periods of time. That's good because it means we enjoy more comfort while using less energy than people did in, say… the 1920s. Houses are tighter now. They're less leaky.
The downside is that all that air tightness keeps stale or putrid odors and potentially harmful gases indoors. For example, the carpet in your living room is probably off-gassing, releasing VOCs into the air. The same goes for the new Ikea bookcase in your kid's bedroom. And then there are smells from your bathroom, kitchen, and basement…
You get it. The list goes on. Old houses didn't have these problems. Newer ones do.
You're already ventilating your home, kinda sorta.
If you've got central HVAC, you don't want to open windows all the time. You want air filters to keep the air clean and refrigerant or natural gas to keep you cozy. So, how do you ventilate while avoiding the pitfalls we discussed earlier?
Believe it or not, you might not have to do anything.
Unless you live in a high performance, "green" home or you've made significant improvements to your home's envelope, air leaks throughout the structure are already providing a near-constant exchange of air. Technically speaking, this is enough ventilation.
But what does "enough" mean?
Thanks to the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE), we have a ventilation standard for buildings. It's known as ASHRAE Standard 62.2, and following it has actually become a code requirement in some places.
Without going into too much detail, most homes leak enough to meet this basic standard for "enough" ventilation. It's a low bar to clear, though, and many people want a more sophisticated ventilation method to improve indoor air quality and comfort.
If that sounds like you, where do you start?
These are your best options for mechanical ventilation
The most common types of mechanical ventilation are the negative pressure solutions found in most homes: bath and kitchen fans.
As noted above, any time you run one of these fans, you unwittingly bring in unfiltered air from the outdoors (or your attic or crawlspace) to replace the air you exhausted. That air probably isn't very clean.
Thankfully, positive pressure or balanced ventilation solutions allow you to bring in fresh, filtered air from outside. Instead of forcing dirtier air into your home through gaps in the envelope, you actually force the "old" air out through those same gaps. Or, if you're using a balanced system, the old air exits through the ventilation equipment.
In our climate zone, the two most sensible mechanical ventilation options are:
- Whole-house dehumidifier with fresh air: This one gives you the most bang for your buck, in large part because you get the benefit of dehumidification. Here in Georgia, the humidity can be downright oppressive for much of the year! In addition to removing humidity to your specifications, whole-house dehumidifiers can bring in a certain amount of fresh air every hour. They connect to a mechanical damper that opens any time you need ventilation. Note that this is a positive pressure solution. When the system is running, the air being replaced will escape through gaps in the envelope.
- Energy recovery ventilator, or ERV: These are great options for high performance homes. An ERV isn't a positive pressure ventilation option - it's a balanced system. It brings in and exhausts air at the same time, relieving the home of some humidity in the process (although not dehumidifying as we explain here). To see whether you need one, we use tools, equations, and building science standards to measure how tight or leaky a home is. In really tight homes, you might need an ERV. The numbers will tell us for sure.
Most homes don't need an ERV, though. They make the most sense in super airtight, high performance construction.
The whole-house ventilating dehumidifier, however, is a fantastic choice for most homes in our area! You rid the home of humid, stinky, pollutant-saturated and allergen-laden air while introducing fresh, dehumidified, healthy air.
Once you've got one, it'll feel like a miracle. No kidding.
So, should you spend a lot of time fretting over ventilation?
Maybe, but maybe not. Here are our recommendations:
- Do you care about indoor air quality? Then some improvements might be in order. A whole-house dehumidifier can drastically reduce the allergens in your home (dust mites don't like dry environments!) and continuously exchange stale air with fresh, filtered air. It's a much cleaner way to ventilate when compared to opening windows or running an exhaust fan.
- Are you planning to air seal your attic and/or encapsulate your crawlspace? You're tightening up the building envelope, so you might need a mechanical solution for ventilation. We perform tests to see if your home meets ASHRAE 62.2. If it doesn't, you'll need some kind of ventilation system.
- If you bought a high performance home, you might need mechanical ventilation. A lot of new homes are super airtight and require mechanical ventilation. A balanced system, like an ERV, is usually a good choice. If you're not sure whether you've got enough ventilation - and you're concerned about indoor air quality - it's a good idea to test your rates of air exchange.
And if it's a nice day with low humidity and a low pollen count, you might even consider opening a window. We know. Radical option, right?
Today's homes aren't nearly as drafty as homes built 75 years ago, and that's a good thing. Just know tighter homes make ventilation a little more tricky. The best ventilation choice for you really depends on your home - and your priorities.
That, in the end, is the crazy truth.