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  1. #1
    Join Date
    Nov 2017
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    help me make sense of this - VOC levels

    I've been tracking VOC levels in my home using Awair for the past week. I found that when I run my furnace heat, VOC levels spike very quickly. When I switch to AC, they drop back down just as fast. If I run the fan only, levels eventually return back to normal, but at a slower rate (compared to AC). Any idea what could be causing this? I also have an HRV that is constantly running in min mode. Humidity levels are about 40-45% indoors. CO2 levels are normal. Outdoor temp is about 50F. All filters are new. I'm also using a UV lamp.

  2. #2
    Join Date
    Dec 2015
    Location
    Austin
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    Two points:
    1. Increasing heat causing an exponential rise in VOCs. Many VOCs are constantly transitioning between between solid/liqauid and gas states. I slight rise in temperature can cause a rapid increase in gas state VOCs.
    In fact that's the rational for *bake outs* to decrease VOC. The idea being to cause VOCs to transition from solid to gas states and then vent them out, collect them (adsorbtion devices) or destroy them via PCO/PECO. Google *Back Outs to Remove VOCs*.

    2. I really wish I could trust the Adware Device and other low cost VOC meters. Not there yet. I discussed the Adware device with the CEO (I think) and he could provide no assurances for accuaracy or calibration.
    A professional PID meter (used to measure VOCs) cost about $8000 and is usually calibrated before each usage. If anyone can attest to the accuracy of these inexpensive alternatives I'd be interesting in hearing.
    The best way to measure VOCs in Gas Chromatography (home air check, Fike)

    Randy

  3. #3
    Join Date
    Jun 2017
    Location
    Rockledge, Florida.
    Posts
    77
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    Quote Originally Posted by kunez View Post
    I've been tracking VOC levels in my home using Awair for the past week. I found that when I run my furnace heat, VOC levels spike very quickly. When I switch to AC, they drop back down just as fast. If I run the fan only, levels eventually return back to normal, but at a slower rate (compared to AC). Any idea what could be causing this? I also have an HRV that is constantly running in min mode. Humidity levels are about 40-45% indoors. CO2 levels are normal. Outdoor temp is about 50F. All filters are new. I'm also using a UV lamp.
    What type of furnace?
    It appears that something is getting hot and generating VOCs possibly a as a result of some thermal decomposition (byproduct of decomposition reaction). This decomposition stops with the furnace off and stops faster when the AC cools the decomposition area faster. Look in the furnace plenum area for visual signs of thermal decomposition.

  4. #4
    Join Date
    Nov 2017
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    Thread Starter
    Thanks for the suggestions! I'm not sure how accurate the monitoring device really is, but the spikes/dips in VOC levels clearly correspond to heating/cooling patterns so there is some correlation. I can see the VOC levels drop immediately as soon as the AC turns on, even before any temperature changes take effect. Additionally, if I run the fan only, the levels will continue to drop slowly even if the temperature in the room stays constant.

    It's a forced air gas furnace. About 10 years old. What are visual signs of thermal decomposition?

    Another thing I've noticed is that the VOC levels are lowest in the finished basement and highest on the 2nd floor.

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