Which reading would you trust?

Hey all, I have 3 grows, and each one has the same equipment for heat and humidity controls. I use the Inkbird humidity controller for humidifiers during the seedling stage, and the AC Infinity fans to exhaust heat and humidity. I’ve had it all for years, and it’s always bothered me there’s always a discrepancy in the relative humidity readings between the AC Infinity controller and the Inkbird, in all 3 spaces. The probes are a couple of inches apart, and the same distance away from the plants. Sometimes it’s only 3 or 4% difference, but other times it’s as much as 8 or 9%. The AC Infinity always thinks it’s higher than the Inkbird. I took pics just now of all 3 set ups and highlighted the differences.
What do you think? Any idea which piece of equipment is more accurate or reliable? For 3 years I’ve been assuming it might be somewhere in between the two numbers.

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Its possible u have a fluctuation problem in ur humidity or ur temp its not much thou i dont think it will be a problem

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It stays pretty stable, I keep a dehumidifier or the air conditioner running in there pretty much 24/7. I just wish I knew which reading was correct.

A man with two watches never knows what time it is. Add a third device and you’ll get a third result. This is an age old problem that every grower has to come to terms with.

My recommendation: Run both sets of numbers thru a VPD calculator and see if you’re within specs on both. If so, choose one and ignore the other(s). If not adjust conditions until you are within spec on both and then choose one and ignore the other.


Find an old school mercury thermometer and see what that says.
I guess there are “analog” humidity meters too.
Just a thought.


So, I’m new to growing (so new I’m still waiting on supplies) but I’m not new to controls.

If you want to know the systematic difference between the two, place the two probes next to each other. If they are both working correctly, they should read close to the same and move up and down together. The difference between the two is a systematic calibration error. Unless you recalibrate them both, assume the average is accurate.

If, when close to each other, one fluctuates a lot and the other doesn’t, one is faulty. You have a 50-50 shot at picking the one that is faulty. I guess with 3 meters, you could put all three together and improve your odds on picking the faulty one.

If they all function properly, as in the first scenario, then the differences you are seeing are in your probe placement. Either:

  • one has more air circulating around it and one has more stagnant air, or
  • one is close to an evapotranspiration source and is affecting the measurement.
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Don’t trust the AC Infinity humidity reading, always says it’s higher than it is. I’ve verified this using my cigar humidor hygrometers (good quality ones), my 2 cigar hygrometers would both say it’s 58RH and the AC Infinity would say it’s like 70RH. At least with the new ACI controller 67 you can calibrate the RH sensor to correct it.


Thank you @Hellraiser, that was the exact thing I was looking for, someone else who who feels the AC Infinity humidity readings are high. That’s the way it’s always seemed to me, but it’s nice to get some confirmation. The probes can be right next to each other and AC Infinity reads 10% higher. I’ll stick with the Inkbird readings from now on.


That’s why I went with the basic controllers after using the enhanced controller.


I’ve noticed the same thing too with my AC Infinity humidity readings. Always higher than my other meters