Ventilation fan sensing

I’ve got several ventilation fans that are not on automated switches (for various reasons). I’m wondering if there’s a decent way to use an esphome setup with some sensors to better monitor if a fan has been left running and raise an alert to go turn it off.

Using a vibration sensor alone is problematic, at least it has been in the past, as passing trucks or other loud outside noises tended to trip it.

I have decent access in the attic to where the ducting runs to leave through the roof.

I’m wondering if some combination of vibration and sound could be used to get me a more predictable detection. Maybe just sound, listening for the rush of air through the duct. I wouldn’t need this to be a constant monitoring situation, something checking every 2 or 3 hours would be fine.

The shorter solution would be to just change out the wall switches for automated ones, but I do like the on-switch timer control that comes with the Lutron Maestro MA-T51MN timers. Otherwise I’d have RRD-8ANS switches controlling them. An esphome setup would no doubt be a lot less expensive than four of them.

There are really 2 ways of doing this. A pressure sensor or a switch to measure the electricity current.

Pressure sensor: We use a differential pressure sensor to measure the pressure across the fan. The suction side will be a negative pressure and the discharge will be a positive pressure. You can use one pressure sensor but it really depends on how big your fan is, so sometimes having a negative and a positive pressure = a higher value. example -10 + 3 = 13pa. So it makes it more stable / accurate. I haven’t used these sensors and I know you can get a pressure sensor that has 2 ports to measure differential pressure but you will need to do some research.

“Measure Electricity current”: So you can use this switch that works perfectly into HA. All local control if you like. You will then be able to use a normal switch and then you can have automations to do anything you like even turn the fan off after x amount of time. This is how I do it, you can forget about the alert and just turn it off.

If I was going to go the switch route I’d just change the existing standalone timer switch to one that would already integrate into my existing network of Lutron Ra2 devices. That and the wiring running to the fans is a switch-leg, without a neutral. The wall boxes are already pretty cramped inside, and I don’t love the idea of burying a gadget in there too. The wiring connections at the fans are inside metal boxes, so I’m not sure how well they’d allow for a WiFi connection into them.

That said, the features of the Plus 1PM are pretty interesting.

fair enough

Shelly 1L no neutral required

I have 2 shelly’s in metal boxes (like heavy switchboard inclosures) about 10 meters away from AP. It works well but it is a bit of a hit and miss kinda thing to your house.

What did you think of the pressure sensor? I decided against it because by the time you get a sensor or two, ESP32, USB cable, power block & power point next to it it was easer & cheaper to install a Shelly and have full control with automation. You can do it using Shelly APP but I do it in HA. For me the pressure sensor would be good for a A/C filter to monitor when they get dirty and need changing.

The point is using the switch inputs to the Shelly won’t work if the Shelly is in the fan’s connection box, instead of in the wall box with the existing switch. There’s no power at the fan, just the two wires of the switch leg.

I’ve decided to bite-the-bullet and have ordered some replacement RRD-8ANS switches to replace the standalone Timers. I’ll lose the local timer control but, honestly, only rarely ever used it outside of a default 30 minute interval. I’ll just use the rollback/occupancy on the zone and use a Lutron scene to delay the fan timer 30 minutes after the lighting. Lutron makes this easy, and I use it in several other zones.

I am, however, going to look into the pressure sensors. I’d like to see if my water heater exhaust stack is properly pulling enough air when other fan ventilation is operating. Modern houses are pretty tight and we don’t have a ‘make up air’ handler integrated with ours. This means there’s a chance the operation of the vent hood over the kitchen range, combined with other exhaust fans, might be able to overwhelm the suction of the powered exhaust fan on the water heater.

I have a fire/carbon monoxide alarm in that room (and in others) and they’ve never tripped. But better safe than sorry. I’m going to see about using the pressure sensors to measure it. It’ll make an interesting project. Once I get the hang of using the sensors I might move on to check the HVAC air duct pressures and see about adjusting the various registers to better manage air distribution.


i usually use this one to monitor other device like pumps or furnace:

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