Airflow sensor to detect HVAC filter change

Hey Guys,

I’m about half way through a remodel, and got some new HVAC equipment installed and was looking at this project for integrating things in my home. One thing on my mind is detecting when my air filter needs changed, either by detecting volts / amps on the blower or reduced airflow in the duct work.

Anyone integrated these kinds of sensors into Open Hab? Is there a typical way to send alerts to my e-mail, phone, or desktop?



I know nothing about what sensors you can use for this. Perhaps something as simple as one of the wireless plugs that reports power usage would be sufficient, assuming it can handle the needed AMPs.

For alerts you have a world of possibilities. Look at the list of Bindings and Actions and choose one you want. These can include email, Pushbullet, Notify My Android, etc. or you can connect to IFTTT and connect to anything that IFTTT connects to.

I don’t know of one out of the box, but I use espEasy on a D1 Mini with MPX5010DP for my air filters and MPX5700DP for my water filters.

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@sipvoip Do you just attach a hose on either side of the filter? Looks like it’s what I have in mind.

You might be overthinking this. Look at the filter itself, there should be a spot where you can write the date installed. Write it on the filter itself. Now, look up the filter, they have a max amount of service expectancy/recommended replacement period. Depending on the rating quality of the filter, this can be 6 months, 1 year, etc. I know this since I just recently replaced mine. Install the filter and set a google reminder to replace it in 6 months.

If your thinking of automating it, there are dust particle sensors out there. Lookup GP2Y1010AU. Hook it up to a microcontroller. I use one to monitor air quality of my 3d printer enclosure to automatically turn on/off the exhaust fan. Not sure you can use this but worth looking into.

Knowing the “state” of the filter requires you know the volumetric capacity of the filter itself. You need to know when to measure the capacity and keep into mind the speed of the fan because lower air volume does not necessarily mean bad filter. It’s just that your HVAC may have had the fan speed at low setting. Also look up differential pressure sensors. THey are primarily used by hotels and other large structures for air filter monitoring. There’s a number of reasons why you don’t see this available already for the general consumers. Just seeing a drop in the pressure could mean anything.

I’ve had problems where I did some work that raised a bunch of dust and clogged up the filter sooner. I agree the 3 months or so on a 1 month filter should be followed. But if I can detect that I’m stressing the blower because I did something that stirred up a bunch of dust and clogged it up sooner, it’d be nice to know that and then just change the filter then. I’d assume that pressure sensor would notice that there’s a larger vacuum after the filter in that case, and when it gets to a certain point I’d just say, OK change it now.

Yep. That’s the idea. The hardest part for you would be the calculations. Like I said, just a drop in pressure does not automatically mean bad air filter. Modern HVAC systems nowadays monitor the temperature through the thermostat. You can set the fan as AUTO or manual. For mine, I have it on auto pretty much the entire year. I let the HVAC decide when to turn on the blower/fan. With the fan blowin, yes you’ll get good pressure buildup and your sensors would be happy. What happens if the HVAC turns the fan off automatically? You’d need to know that too so you can ignore sudden drops in pressure, i.e., only compute when fan is on. You also need to realize HVAC zones. In my home, we have 4 zones, which I can turn the fan on/off specifically for that zone BUT since the ducts are still connected, even if all fans are off except zone 1, I still feel a slight breeze on the other ducts, and since there’s pressure, you have to know what that pressure means.

All differential pressure sensors depend on volumetric flow, which means there’s the ‘flow’ and the state of the flow itself must be known. So if you dont know the state of the flow (blower fan) then you cannot really quantitatively measure teh state of the filter. With an ‘unknown’ state of the flow, the differential pressure does not mean anything at all. It’s like trying to determine if a car is dead or not when you dont even have the keys. The car is ‘off’ but it does not necessarily mean it’s dead.