Getting my garage vent fan to turn on and off based on indoor/outdoor temp

I have been trying to get an automation that will turn on a vent fan when the temperature is outside is cooler than the temperature in the garage. I live in a very hot region of the US where the temperatures can reach 100+ during the day. This heats up my garage in the 90s. I would like to have the vent start bring in outside cooler air when the sun goes down and the outside temperature drops below the garage temp by 3 degrees. I am using HASS.OS v 5.10.42 installed on my NUC.

I found this link Help triggering turning off attic fan when ambient is within 15 degrees of outside which I thought I could use the info and modify it to fit my particular needs. Have no training or background in coding I have tried just about every combination of template with none working.

This is what I have come up with so far to turn on the vent.

alias: Garage Vent On Summer
description: When the Garage is 3 degrees hotter than the outside temp the vent turns on
trigger:
  - platform: template
    value_template: >-
      "{{ state_attr('sensor.garage_temperature1', 'temperature')|float > (
      states('sensor.thermostat_outdoor_temperature')|float -3 ) }}"
condition:
  - condition: template
    value_template: ''' '''
action:
  - service: switch.turn_on
    target:
      entity_id: switch.garage_vent
mode: single

This is what I have come up with to turn it off when outside temp gets 3 degrees warmer than the garage.

alias: 'Garage Vent Off '
description: >-
  Will turn the garage vent off when the outside temperature is three degrees
  warmer than the garage
trigger:
  - platform: template
    value_template: >-
      "{{ state_attr('sensor.thermostat_outdoor_temperature',
      'temperature')|float < ( states('sensor.garage_temperature1')|float -3 )
      }}"
condition:
  - condition: template
    value_template: ''' '''
action:
  - service: switch.turn_off
    target:
      entity_id: switch.garage_vent
mode: single

Any pointers would be greatly appreciated! I think something like this could be used for controlling window fans based on the outside and inside temperatures.

There appears to be a difference in how the two automations get the garage and outdoor temperatures.

In the first automation (to turn on the vent):

  • It uses state_attr() to get the temperature attribute of sensor.garage_temperature1.
  • It uses states() to get the state value of sensor.thermostat_outdoor_temperature.

In the second automation (to turn off the vent), it does the opposite:

  • It uses state_attr() to get the temperature attribute of sensor.thermostat_outdoor_temperature.
  • It uses states() to get the state value of sensor.garage_temperature1.

Check the two sensors (in Developer Tools > States) and determine which one reports its temperature in its state value and which one reports it in its temperature attribute. Use the correct function, states() or state_attr()`, accordingly and consistently in the two automations.

Oh, Thank you so much for your quick response! Such a simple mistake, just shows how beyond my skill set trying to figure something like this out. Everything I do as far as coding is based on others examples. I try my best to modify them for my needs and most of the time it works, but this is an example where my lack of education and training was a decrement! Spending several hours trying to get this to work, I have decided that there may be more variables, conditions, etc. involved than my simple approach! I had difficulty defining what I was wanting the vent to do, which is a must before designing a template. I think I want it the vent to turn on when there is a three-degree differential outside being cooler than the garage and to turn off when it is less than 3 degrees cooler. But figuring out how to write the automation code is another thing! lol Last night I must have put in hundreds of combinations of the following:

"{{ states('sensor.thermostat_outdoor_temperature')|float > ( states('sensor.garage_temperature1')|float +3 ) }}"

"{{ states('sensor.garage_temperature1')|float < ( states('sensor.thermostat_outdoor_temperature')|float -3 ) }}"

I was also not sure what:

condition:
  - condition: template
    value_template: ''' '''

was for or if it was needed (again just what I got from an example I was trying to modify).

None of them seem to have the desired effect. But I learned something about how to use the “state” in setting up a template! Hopefully someone will write a blueprint to for all the rest of us with minimal coding skills, but a passion for HA and home automation!

If my reply has helped to correct the error, please consider marking my post (above) with the Solution tag. It will automatically place a check-mark next to the topic’s title which signals to other users that this topic has been resolved. This helps users find answers to similar questions.