Over the past few years, I have been experimenting with air filtration in our home. In recent years, the onslaught of summer fires in the pacific northwest has made air quality poor and unhealthy for our family. The COVID-19 pandemic has brought filtration and ventilation to the forefront of my thoughts. I wanted to summarize what I have done and which products I am using to combat poor air quality and poor air circulation.

Your Home HVAC System

Every home has some heating and cooling system. If yours is forced air (meaning you have a furnace and air blower), you have a filter.

If you have a newer house, you also have a fresh air ventilator - a device that is designed to bring fresh air from outside into your home.

Bring in fresh air from outside poses a problem. That air can be cooler or warmer than your home. It can contain smoke particles during a fire. Also, you have to think about exhaust - moving air out of your home. These two ideas, ventilation and exhaust, work in tandem to "exchange the air" in your home. There are formulas for how much air you are supposed to exchange per day.

Ventilation and exhaust make for a "balanced" ventilation system.

Your furnace filter

Our furnace came with an electrostatic filter. This uses electricity to "zap" air particles. It seems fancy, but it's garbage. We replaced ours with a good old fashioned filter that traps particles. We replace it every three months. No cleaning at all; toss the old filter and pop in the new one.

These filters are measured using a MERV scale. I use a MERV 11 filter as this balances my system's performance and the particles it removes. The big difference between MERV 11 and MERV 13 is that MERV 13 will remove viruses and bacteria.

I also use an ecobee thermostat (more on that later), and they have a subscription service for your air filters. It's pricey, so I get mine from Amazon. Our ecobee reminds us every three months to replace our filter.

Ventilation

Our home came with a mechanical ventilator connected to a timer. I rewired it to connect to my ecobee thermostat. The ecobee then runs the ventilator for 15 minutes every hour, bringing fresh (cold or hot) air into the house. This can cause the temperature to fluctuate, so the heater and AC might run more often.

I like this, though, cause it also means my furnace is rebalancing the air throughout the home.

If you are lucky, you have a fresh air exchanger in your house. This brings outside air into your home at the same temperature as the inside air. We don't have one of these, but I would put one in if I was building a house from scratch.

Balanced Air

With all this fresh air coming into the house, you need to get stale air out of your home. You can do this two ways: 1) open a window 2) run your exhaust fans.

Every home has exhaust fans in bathrooms and individual rooms in your house. Ours has one in our basement laundry room, and it has a timer. However, I installed timers on all our exhaust fans, and they run on a schedule to remove stale air and send it out of our home.

The Honeywell Digital Bath Fan control allows for this style of programming.

All of this stuff is covered by the ANSI/ASHRAE Standard 62.1-2019

Thermostat

My ecobee thermostat controls temperature and ventilation. Ecobee has remote sensors that I placed in numerous rooms in our home so that the house is the temp we wish in the right rooms vs. the location of the thermostat.

Air Filtration

One of the best wirecutter reviews is the air purifier review.

In our home we have the following air purifiers:

Coway AP-1512HH - in our kitchen and bedroom. This unit can purify a space up to 361 sq. ft.

Coway Airmega 150 - in our kid’s bedrooms. This unit can purify a space up to 214 sq. ft.

Coway Airmega 300 - in our living and dining room. This unit can purify a space up to 1,256 sq. ft.

It’s important to match your air purifier with the size room it will occupy. In general, what you need to know is how many times in an hour will it cycle through all the air in the room. The sq. ft. assumptions below are for a room with 8ft ceilings - so you need to also factor this in. It’s better to go up a size as that also allows you to run the unit on its quietest setting but still cycle all the air frequently.

I have owned and tried other air filters

All the Dyson ones
The BlueAir 211+
The Molekule

Here is why I like the Coway units

Filter replacement is simple and easy. You replace the HEPA filter once a year and, in some cases, the carbon filter 2x a year or 1x a year
They all run on auto - which ramps up and down the air filtration based on its sensor. This works great for our kitchen
They are near-silent
They have simple controls.
Their replacement costs are low

One of the great things about air purifiers is that they clean the air of smell. Adding an air purifier to our Kitchen was one of the best decisions we made as it really helps out when we cook smelly food such as bacon.

What about the others?

Dyson - expensive, looks great, acts as a fan, and in some cases, a heater. I like the Hot / Cool model and have it in my office. It's crazy expensive but built like a tank. The older models have an issue where the motor that results in oscillation will wear out and make horrible sounds. Their filter replacements are pricey.

My advice, get a simple air purifier with easy replacement medium and invest in a fan if you want a fan in your room.

BlueAir 211+ - very dumb. No auto mode. Noisy. Large. Ugly.

Molekule - fancy garbage. Not HEPA. Questionable business ethics and debunked as being an air purifier.

Measuring Air Quality

I've recently learned that the best indicator to pay attention to is CO2 levels. This is especially true for COVID-19 since it's an airborne particle that spreads the virus. As such, you want adequate ventilation (which is why everything outdoors is usually OK), and for indoors, you want to wear a good mask (N95 if ventilation is low). The mask will trap the virus on the way in or out.

One of the reasons airplanes are believed to be less of a threat to the virus's spread is that planes have sound ventilation systems (fresh air comes in, and HEPA filters remove particles).

I use the following devices to measure CO2 levels:

Aranet4

I recently purchased a few of these and kept them around my house. These are very sensitive units and can update every 2/5/10 minutes. They are also portable, and you can take them with you to monitor CO2. If CO2 reaches greater than 1000ppm (parts per million), then you have cause for concern and should open a window or circulate air.

Aranet has put together a great PDF explaining how a CO2 sensor can help protect you against the spread of COVID.

"Aranet4 is an easy to use CO2 monitoring device that lets you know right away if the ventilation is sufficient and whether you are at an elevated risk of SARS-CoV-2 infection via aerosols. Visual color indicators, as well as an alarm, will notify you when action (opening windows, turning up the ventilation, or leaving the room all together) must be taken."

The only place that I have found to purchase an Aranet4 device is from Naltic Industries. You simply fill out a form, and they will contact you for payment.

Netatmo

Netatmo makes a great Weatherstation device that works with Apple HomeKit. The base unit comes with an outdoor sensor that measures outdoor temperature, pressure, humidity and can also measure wind and rain with accessories. The sensor can also be used in certain weather apps such as Carrot (best weather app by far), so you get hyper-local information!

Netatmo can be extended with additional indoor modules (up to 3) that measure CO2.

I have purchased the base kit, three additional indoor sensors and now monitoring four rooms in my house.

I have found that the Netatmo CO2 measurement is not as accurate as my Aranet4. It appears to undercount by about 20-30%. I have emailed them to understand more about why such a significant discrepancy.

Summary

There are a lot of ways that you can take steps to improve the air quality in your home. First, you need to measure the quality, next you need to get your existing products to work correctly (HVAC filter, ventilator, exhaust) for balanced air, and then you need to ensure you have air purifiers in the right places (bedroom, kitchen).