How to Actually Measure Your Indoor Air Quality (Stop Guessing)

Homeowners measure square footage, mortgage rates and paint colors. Almost nobody measures the air their family breathes all day. It isn’t because it’s hard. It’s because for most of my career the industry never asked them to.

The old process went like this. The homeowner describes a symptom, the technician recommends a product, the product gets installed and everybody hopes for the best. Nobody measured anything before, during or after. I don’t work that way anymore, and I don’t think you should accept it from any contractor.

Your body is a bad sensor for this. You get used to a stuffy room. You blame feeling tired on work. A family can live with slowly declining air for years and only notice after a trip away, when they walk back in the door and the house feels different.

Even when you notice something is off, you can’t tell what it is. Stuffiness could be humidity. It could be CO2. It could be particles. It could be all three. Without data, a contractor is just guessing differently than you are.

There’s a short list that tells you most of what you need to know.

• Temperature and relative humidity in each main area of the house. Aim for 30 to 50 percent humidity in winter and 40 to 55 percent in summer.
• Fine particulate matter, PM2.5. These particles are small enough to get deep into the lungs. When PM2.5 climbs, something like cooking, candles or outdoor smoke is beating your filtration.
• Carbon dioxide. CO2 tells you how much of the air you’re breathing is exhaled air instead of fresh air. Outdoors runs around 420 parts per million. Indoors should generally stay under 1,000 ppm in occupied rooms, and ideally under 800.
• Total VOCs. A consumer sensor won’t tell you exactly which chemicals are in the air, but it will show you when something spikes, like new furniture, cleaning products, air fresheners or cooking, and by how much.
• Carbon monoxide. Every home with a gas, oil, propane or wood-burning appliance needs CO monitoring, ideally a low-level monitor that alerts well below the levels standard detectors wait for.
• Radon, if your area calls for it. Short-term test kits are cheap and easy, long-term tests are more accurate, and your state or local health department can tell you your radon zone.

Bedrooms at night are often the worst room in the house on CO2. Two adults sleeping with the door closed can push it well past 1,000 ppm by morning, and you’ll never smell it. You might feel it as a groggy start to the day.

A one-time test is good. Continuous monitoring is better. Modern home air monitors are affordable, easy to set up, and track temperature, humidity, PM2.5, CO2 and VOCs around the clock. You can see how your air changes over a day, across the seasons, and every time you cook or run the dryer.

I recommend at least one monitor for any family that cares about its air, and more than one in larger homes or houses with a problem area. Brands worth looking at include Airthings, uHoo, IQAir AirVisual and Awair. They don’t all measure the same things, so check what each one reads, but any of them gives you visibility you didn’t have before.

What a home monitor can’t do is tell you why. A professional assessment adds the HVAC side: static pressure across the air handler, airflow at the supply registers, duct condition, how the filter is housed, combustion safety on gas appliances, and temperature and humidity room by room. That’s the part that connects a bad number to a fix.

A number on its own doesn’t mean much. The pattern is what matters.

A PM2.5 reading of 20 isn’t alarming by itself. A reading of 20 that shows up every evening when dinner’s on the stove and doesn’t come down until morning tells you the kitchen isn’t venting and the filtration can’t catch up. Same number, completely different conversation.

CO2 at 1,400 in the main bedroom at four in the morning tells you that room isn’t getting enough fresh air with the door closed. That’s something you can act on, with ventilation, with how the door gets used at night, or both.

Once you have readings, they point you toward the fix:

• High CO2 points to ventilation.
• High PM2.5 points to filtration and source control.
• Humidity out of range points to humidity control, and sometimes to an oversized air conditioner.
• One room that reads badly while the rest of the house looks fine points to a duct or return-air problem in that room.

That’s why we put testing results on a single page for our clients: their readings, side by side with healthy ranges. It isn’t a sales sheet. It’s often the first clear picture a family has ever had of their own air, and it turns the conversation from selling a bigger box to fixing the problem the house actually has.