Attic Fan - Constantly On

I’m a fairly new Sense user (little over a month in) and 8ve found it very useful to see what is consuming so much electricity.

Ive recently discovered that it seems my attic fan is runing indefinitely. Sense hasn’t discovered it, but that’s likely because it’s always on. It draws about 230w. It has a temp and humidity sensor, and I tried adjusting the humidity sensor, but I need to raise it to almost 70% to get it to shut off. It’s the middle of winter in NJ and we struggle to keep the relative humidity at 40% in the winter inside the house. I know attics can be different, but perhaps this switch is faulty? Or just inaccurate?

I wish there was a point inline sensor I could add to some devices. I’ve added several TPLink plugs and power strips that sync with Sense…

Thoughts? At 230w, it’s definitely adding to the power bill significantly, running 24x7. I do have Sense to thank for helping me track this down.

You’re talking about a true attic fan that is just drawing air through the roof space or is it a whole-house fan that is pulling fresh air into the conditioned space? I assume the former.

In that case my limited understanding is that there’s a tricky correlation between RH and temp … in winter you probably only want the fan on when the internal RH is high AND the temp is over a certain minimum AND the outside RH is lower. Dew point!

Without going deep, my thought would be to switch it off for now and give yourself enough time to come up with a Sense-driven smart control by summer!

I’m guessing others will weigh in with some practical options in that regard.

Attic fan efficacy is a hotly debated topic in the field of home energy performance, so get ready to hear some conflicting opinions!

Humidity control using an attic fan in New Jersey is, IMO, a futile endeavor. The “correct” humidity level for the attic is equal to the outdoor humidity, so setting a fixed value will have no purpose other than to waste energy. So, I’d set that to the max so that only the temperature control is active.

Now, as to whether the attic fan should be there in the first place: if you have good passive venting (clear soffit vents combined with a ridge vent and/or gable vents), I’m of the opinion that a fan is not needed. If you have poor passive venting, then the fan may be a good tool to get by until the next time the roof is replaced and venting can be added. Also, make sure that you don’t have any exhaust fans from within the house venting directly into the attic.

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I’ve experienced your exact situation, regarding my Attic Fan - here in the Northeast Ohio area! I elected to sever the original single inline power source.

  • An electrician installed an outlet, leading from the power source
  • Affixed a plug on the line, leading to the Attic Fan
  • Leveraged a Smart Plug into the newly installed outlet
  • Inserted the new plug into the Smart Plug

This action afforded me complete automated control of the Attic Fan. This low-cost effort gave me a significant reduction in my “Always On” value and monthly energy consumption - not to mention ensuring a mold-free attic area!,

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Thank you all for your advice. Yes, I’ve read some debate on the usefulness of attic fans. I find it’s number one usage is quickly pulling hot air from the house when cooling in the summer.

I am keen on the idea of putting a plug on the end so I can use a smart power switch. I think for the time I’ll set the humidity control all the way up and do some additional research.

I wholly concur.

I would also put some temp/humidity sensors in the roof space and try to quantify things.
A constant-on fan at 200W is probably costing around 20+/month. Any roof work is going to cost significant time and/or .
Investment in some good sensors will save you grief and money in the near term.
This would be my “fancy” pick for reading temp & humidity, if only because I’ve used them in a commercial building management setting, but there are plenty of cheaper options: https://www.monnit.com/Products/Wireless-Sensors/ALTA-AA/Wireless-Humidity-Sensors

That said, as @pswired hints at: you could just switch off the fan, at least until summer … and stick your head in the roof space periodically and see/sniff how it looks and feels.

There are a few issues with attic fans:

-They use a lot of power
-They become a fire hazard when the motor reaches end of life and seizes up
-If there isn’t sufficient ventilation in the attic to provide makeup air, they will depressurize the attic and draw out conditioned air from the living space, increasing the HVAC system load

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