Monitor HVAC air filter status?

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1

Is anyone using something to monitor HVAC air filter status? I have to get up in the attic to check the filter. It's an Aprilaire accordion-type filter that is inconvenient to remove.

Maybe a barometric pressure sensor on either side of the filter and follow the pressure drop.

I've even considered putting a cheap cam and LED light in the duct so I can look at the filter remotely.

Any other ideas?

2

Two options here...

https://www.bapihvac.com/products/pressure-sensors/pressure-differential-switch/

Pretty standard stuff for commercial or industrial application. Could be used with a Zooz Zen17 or similar to monitor the switch contacts. Might be tricky to get the setpoint dialed in just right.

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3

Looks perfect.
Only $25 and some fiddling.

4

I use two temperature sensors 1 mounted inside a supply duct and the other mounted inside the return duct. Which gives me the deltaT temperature difference, when the HVAC is running. You get a baseline temp difference when you put in a new filter (general rule of thumb for a properly sized system is between 16-24 degrees for cooling), and when that difference begins decreasing from your baseline generally indicates the filter is getting dirty (given you don't typically have freon leaks or other problems with your unit)

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5

This was my first thought. I wyze cam v3.

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6

Are you mounting it in just any supply duct, or one close to the return? What sensors are you using?

7

Are you able to track the operating time of the HVAC fan?
My gut feel is that this would be a pretty good proxy for filter life, unless you have a major influx of pollutants at different times of the year.

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I'm using the supply closest to the hvac unit. I have an Iris V3 contact sensor in the return since it can only update temp is every 5 minutes and the return air temp doesn't change much during hvac cycles. On the supply side I'm using an old Fibaro FGK-101 with an external DS18B820 temperature probe that updates temperature every 0.54 degrees or 1 minute.

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9

Operating time of the HVAC fan will vary drastically based upon the inside/outside temperature difference causing shorter/longer run cycles.

However I do track my cycle times for my own general FYI, and charting with grafana.

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10

Once this 22.45 starts getting in the 14-18 it's time to change the filter

deltaT
deltaT1830×884 100 KB

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11

I hate to be that guy, but what did you use for the dashboard? I'm still not doing anything even remotely pretty w\ dashboards, and the wife keeps reminding me the tiles are only one step above Windows 95...

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That is a chart in grafana, ran off a qnap nas.

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Hello @waynespringer79 :slight_smile:
Im very interested in where exactly to put these two temperature sensors.

  1. Living in a cold climate, I have my AC running only certain times of the year (the furnace is on at other times). Does this method work when the furnace is running?
  2. Can I put my two sensors, just on either side of the filter? Separated by the filter, and 1-2 feet? Would that do the trick?
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Yes it works for the furnace as well, however the deltaT temperature is significantly higher and varies depending on individual furnace specs. Mine is I believe between 50-65 degree range.

No, you really need one on the return side (before filter) not as particular to the exact location as the return air doesn't drastically change temp as much as the supply side does, and the supply temp sensor somewhere after your A-coil (A/C) and Heat Exchanger (Furnace) preferably as close in-line to them.

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