Which IAQ Monitor Should I Buy? Part 1

  • Posted in Default
  • By Pan Chaoyang
  • Date December 1st, 2015 11:36
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  • Lately, it seems there isn’t a day that goes by without having someone ask which IAQ (Indoor Air Quality) monitor they should buy.

    As with all good questions, the answer is “it depends”. It depends on what that someone needs: a consumer toy, a precision instrument or something in between?

    10 years ago it was simple: there was virtually only one option to choose from. Today, a new option appears every week. Here is a simplified version of what to look out for:

    "The general rule of thumb is that if it can’t be re-calibrated, don’t buy it."

    Accuracy: “How accurate is it?”  This is everyone’s first question… and usually their last. In the world of consumer monitors, the question is answered by having a sales person hold the monitor up next to an expensive scientific grade monitor and show that the readings are almost the same, for a fraction of the price. This isn’t a very difficult feat to accomplish. The key questions are: how accurate is the monitor over a given range, how quickly does it drift (de-calibrate) and most importantly, can it be re-calibrated?

    Range: All monitors work best within a given range. For consumer monitors the range is typically quite narrow. Whereas accuracy may be within 20% at low levels of pollutants, the level of accuracy drops rapidly at higher levels. Many monitors also have a ceiling, meaning a limit beyond which they can no longer measure. For example, we have seen many monitors for particulate matter cap out at 50-65 µg/m3, when actual indoor readings are 2X or even 5X that. These monitors are dangerous seeing as the give a false sense of security.

    Drift: All monitors drift or de-calibrate over time. The question is how much and how fast? The better ones drift by 5-25% within a year. The worst drift by the same amount within a week.

    Calibration: Seeing as all monitors drift over time, the ability to recalibrate a monitor is critical. The general rule of thumb is that if it can’t be re-calibrated, don’t buy it. Without re-calibration it is destined to become a door-stop or paper-weight within a few weeks to a few months. The challenge is that recalibration is typically more expensive than the average consumer monitor. In other words, if you’re buying a consumer unit it will typically cost you less to throw it out and buy a new one after a few months. That’s irresponsible.

    One last important consideration is quality control. Unfortunately, this is not a metric usually found in monitor specifications. Rather, it follows the ‘you get what you pay for’ rule of thumb. Even when similar hardware is used, the lower price-point of consumer monitors does not allow for extensive quality control. The result is that units can vary greatly from one to the other and / or moving parts such as internal fans can start to rattle or jam over time.

    For these reasons (and more) RESET™ classifies IAQ monitors according to three tiers of performance:
    - Grade A: Scientific
    - Grade B: Building
    - Grade C: Consumer

    Previously, the market for IAQ monitors was almost exclusively Grade A. However, over the past 18 months the market has been flooded with Grade C monitors. We encourage people to stay away from consumer grade units given their tendency to give false readings after a few weeks to a few months. With a little more time and education what the bulk of the market will demand is Grade B monitors, providing the best ratio of cost for performance. Unfortunately there are still very few Grade B options on the market. Users are only just starting to learn the hard way (after spending money) that Grade C units don’t work over time.

    If you’ve read this far you’re probably thinking, “This is great, but I still want to know which unit I should buy.” For now, this post has become long enough! Please read the next post to learn about brands we've reviewed.
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