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as the title: i have a room with with a heat generation that i need to keep under a certain temperature. Anyhow, i want to grant a minimum of air circulation even if the temperature is not reached (winter scenario) and i thought it can be a good idea to connect a thermostat and a timer in parallel to the air extractor (set for 10 minutes every 2/3 hours for example). In this scenario, if the temperature is reached, the fan is working thanks to the thermostat, if is not reached for as long as 2 hours, the fan is activated by the timer.

Thanks for help!

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Jacopo
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  • What's your question? Do you want to know *if* it can be done, or *how* to do it? – Tester101 Jun 28 '16 at 17:26
  • I want to know if it's not a potential dangerous hazard situation. I know the cable connection to do. Thanks – Jacopo Jun 28 '16 at 17:40
  • No, it's not a duplicate, he has a completely different problem. Seriously. The linked problen is a plain switch - no neutral. This one needs a powered switch, which makes it a completely different kettle of fish. – Harper - Reinstate Monica Jun 29 '16 at 17:42

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When it calls for fan, the thermostat is going to short the R wire to the fan-control wire.

You are proposing a timer which also shorts the R wire to the fan-control wire.

Assuming it's all this simple.

For the timer, easy enough: use any common lamp timer which allows hourly on/off. Plug a "wall wart" type transformer into that which makes 24VAC. Then add a 24V relay in the right place that connects R to the fan-control wire. This way everything is Code and the most vulnerable component - the timer - is easily replaced.

The arm-waving magic inside the furnace is what concerns me. If you want help with that, you'll need to be a lot more specific.

Harper - Reinstate Monica
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  • Hi, i added a picture to the question on the top. The first one is the idea i had in mind, the second one is what i understand from your answer. If i get it right, the point is to put a more reliable relay over the cheap timer to prevent shortcuts? – Jacopo Jun 29 '16 at 05:55
  • P.S.: having dc involved and to have a better control i'm also considering switching all together to an Arduino like system with temperature sensor and a proper OR logic port. My point was to make it simple and reliable – Jacopo Jun 29 '16 at 06:06
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    I think i also found a similar setup question: – Jacopo Jun 29 '16 at 06:24