first determine if it is the thermostat or the humidstat causing the fan to go on - so, change the thermostat to a setting that you know will not cause it to engage; then if it goes on then you know it is the humidstat. If it is the humidstat, check that it is set to higher than 50 RH this time of year - the lower the air tempature the lower the RH level. If it doesn't go on then you know it was the original thermostat setting.

Anonymous wrote:OP here. No, no one is taking a shower at that time. Who do I call for this kind of troubleshooting? I know that the roofing company we hired certainly does not do this kind of troubleshooting.

Look for an HVAC maintenance company. Get whomever you have do your annual furnace/heat pump/AC checkup to come and take a look.

The thermostat on the attic fan might be set wrong or broken. Ours is set to turn on when it reaches 90 degrees fahrenheit, so it shouldn't be running now. We had a switch installed in our bedroom so we can just flip it off during this time of year. I'd have yours checked out.

Anonymous wrote:OP here. What confuses me is that the fan would run in the early morning (like 6am!) when it seems cold.

We lived in a three story house with the master bedroom on the third floor. It always got really hot in the early morning (around 5 am), because it was cold downstairs (where the thermostat was) and the heat would come on. However, it wasn't cold upstairs, because the heat rising heat from downstairs kept it nice and warm -- until the heat came on and then it was HOT. We closed all our vents upstairs in the wintertime, but finally got a programmable thermostat and set it to a really low temp in the early am. Just saying that sometimes odd things happen with temperature distribution.

OP here. No, no one is taking a shower at that time. Who do I call for this kind of troubleshooting? I know that the roofing company we hired certainly does not do this kind of troubleshooting.

Is anyone taking a shower when it is on? Is the vent in the bathroom running at the same time? I'm going to bet (if you answer yes to the shower and the vent running) that the bathroom vent is not properly installed and it is venting directly into your attic. That would raise the temperature and the humidity.

sounds like you need a technician.

OP here. What confuses me is that the fan would run in the early morning (like 6am!) when it seems cold.

Wait until it gets really cold and see. It has actually been pretty warm most days lately, and the heat pump on the third floor of our house is still running on A/C. When the sun comes up and warms the attic, there may be enough warmth/humidity to trigger it.

Seems like it's basically just sucking the heat out of your house and blowing it outside. Doesn't make sense for it to be running this time of year.

I can't imagine why the fan would run when it is not hot.

We had an attic fan installed this past summer. It has a humidity and temperature reading and will turn on automatically when needed. We have corrected settings to manufacturer recommendation. The fan comes on every morning. It doesn't seem to make sense to me given the temperature is cold and the humidity should be relatively low this time of year. So I am curious if other homeowners' attic fans that have humidity settings are also running this time of year? TIA.