Which air purifier should I choose for my home?  Part 1: Airflow

We get this question a lot, and truly, we understand how daunting the choices can be.  At HypoAir, we will guide you with a personalized plan according to your home or living space.  The best thing you can do to find that optimal air purifier, then, is to know the space you’re trying to purify, which mainly depends on airflow. 

Maybe you’ve watched a video during science class that shows someone adding a drop of dye to a glass of water and watching it slowly change the color of the whole glass to blue or red.  There are some similarities, but unfortunately it’s not that easy!  The spaces in your home are divided by walls and doors.  You may be in your home office with the door closed while your partner is cooking dinner, and start to smell good things.  The aromas are making it through the ventilation and around the door, but does that mean that the whole home is experiencing the same air quality?  No, because as soon as you open the door and start to walk toward the kitchen, the good smell may intensify, and you may experience other smells along the way (like the cat litter box in the laundry room–ugh!).  Unless you live in well-ventilated (moving air) studio, our home’s IAQ is by no means homogenous. 

Airflow also varies by season and time of day.  Writing this post, I am seated in my home’s sunroom during the winter.   The sunroom is a beautiful but poorly insulated part of my home.  I live in the southeast US, which on this day in February had a low of 33 degF last night, and I high of 70 degF today.  To make this room more usable in the winter, I use a wood pellet stove to heat it on chilly mornings.  The stove blows hot air straight out, and I keep the two ceiling fans rotating at low clockwise to bring the heat down from the ceiling.  When the outside temperature gets above 65 (which was about 11am today) then I can shut the stove off and even open some outside windows to let fresh air in.  Sitting in the middle of this long room, I feel comfortable, but I know that the ends and corners are definitely not receiving the same heat and ventilation!

Optimizing your home’s ventilation does a lot for its IAQ.  The National Center for Healthy Housing identifies two types of ventilation that can be used to improve IAQ: spot ventilation and dilution ventilation.  Spot ventilation includes bathroom and cookstove exhaust fans, which pull odors and harmful combustion by-products out of your air during the use of those spaces.    Dilution ventilation conditions for your entire home through 1) air changes and 2) air cleaning.  Dilution ventilation is the workhorse that really makes or breaks IAQ.  Air changes are necessary; by adding fresh air (about 0.35% of the home’s volume per hour), harmful contaminants are diluted.  If your air feels “stale” then a good place to start can be by opening some windows on the opposite ends of the home  (provided the air quality outside is better), making sure your HVAC filter is in a clean state, and turning on the HVAC fan only, to circulate fresh air into all areas of your home. 

This leads into the next question: can I ventilate with open windows and purify at the same time?  The answer is for the most part: Yes, with common sense applied.  If you live in a high-traffic area, rush hour probably has worse air quality outside, so don’t let that polluted air in during rush hour.  If you live in the country as I do, you can open windows whenever the pollen, temperature and humidity outside are not overwhelming.  Fresh clean air is always needed to dilute polluted air inside, and actually helps your HypoAir purifier because the object is to take what’s good about outside air, and bring it in.  The important part is getting the mixing going!  Open bedroom and bathroom doors when possible, use room fans, or your AC fan set to “on” (not “auto”), to get good airflow going.  

This may seem like a lot of work just to achieve good dilution ventilation, and you’re right, it can be!  It shows that the evolution of home design actually went backwards in some respects.  While living in the New Orleans area for 10+ years, I took several plantation home tours when friends were visiting.  These magnificent homes were smartly designed in many ways.  High ceilings allowed the heat to rise and take in more cool air through doors and windows, creating a natural circulation within rooms.  Windows and doors on opposite ends of the house could be opened to induce cross-ventilation.  Transom windows over doors could be opened for ventilation even if the door was closed.  Porches shaded the home’s interior from the heat during the hottest part of the day.  Longwood, a unique antebellum home in Natchez Mississippi is octagonal; although it was never finished, there is a main rotunda that joins all the six floors to create a convective current to sweep summer heat up and out of the house.  Even the octagonal design has no corners of dead air in each room.  Our recent ancestors may not have had ways to deal with dustmites, pollen and particulates, but they certainly made the most of dilution ventilation, even without electricity.  I grew up in a home in Maryland (hot sticky summers) with one window AC unit and a whole-house attic ventilation fan.  What did we use the most?  For sure, it was that attic fan.  My sister and I would be summoned to open windows on the first and second floor and turn on the behemoth louvered fan, and the fresh air would start to flow in and cool the house in preparation for bedtime.

Enough of the olden days…! How can I accomplish good dilution ventilation with a minimum of effort?  

  • You don’t need to have screens in all windows, but a select number of windows should have clean screens and be easily opened.  Consider installing allergen-filtering window screens in these windows at least.  
  • You can add smart controls to your ceiling fans so that all can be turned on via an app on your phone.  This review gives the details on which smart products will work with the fans in your home. 
  • Smart thermostats can also remotely switch the fan to “on” from “auto” 
  • Place floor fans strategically where there seems to be no air movement. 
  • Tackle the problem of closed doors.  Sometimes it’s not always possible to open every door–like at night, when privacy, sound or light issues warrant bedroom doors to be closed.  The AC fan creates positive pressure in the bedroom, while the air handler is trying to suck the air through a little ½” gap under the door (in most cases it’s just not enough of a gap).   The solution is to install these In-Door Return Pathways, which are easy to install and allow air to circulate more freely through your home.  Bathroom doors are perfect for these too.
  • When it’s not possible to open windows due to rain, temperature or outside air pollution, visit our post “Fresh Air Intakes for HVAC” to see what’s available in letting your AC bring the fresh air in.

Next: check out our Part 2: Air Cleaning section to read the rest of Which purifier unit should I choose for my home?