For the first time this year I came home to hearing the attic fan running. It had run about a week or so ago because I saw my damper had been pushed out, but last night was the first time I came home from work to it running. Ah, free heat, I like it.

Since we've been getting more sun these days, my basement-warmer has been running
for hours, every sunny or partly sunny day..

It was actually running more hours than I wanted..

However on this sunny day, it's going to come on around noon time.
It's now running less hours, because I have the set-point at 20 deg F, above the basement temperature.

Why did you not want it running?

If I recall, my differential is set to somewhere around 3C/5F.

The noise and power use. I have not tried to put speed controls on the motors yet.
Maybe make them a bit less jet-like.
So running them less hours is the compromise, for now.

Edit:
One other reason I don't like to use a small differential,
is blowing 70+ deg air downstairs is a lot more effective at space heating, than 55 deg air.
I think it's a more effective use of electricity.

The blowers came on at noon today and just shut down at 5:54 PM.
That's a pretty long time. And, it was all 70F and above air.. :D

Lately, I've been having some issues with my attic fan controller, a DIY arduino differential temperature controller. The fans will turn on and off a LOT unless it is really hot up there. What I believe is happening is there is noise on the long sensor wire run to the kitchen which makes the temperature signal bounce around. I originally had this problem, so I put a small capacitor on the wire and it seemed to work... for a while. I'll be updating my thread on the controller to show how I'm going to fix it once and for all.

I used to have problems with temperature sensors (solar HW) that used NTC resistors.
Whenever I used ham radio transmitters, I would get some pump relay chatter..
I used ferrite bead filters and got rid of most of the problem.
I obtained the filters from old VGA cables..
Ferrite Beads on A/V Cables: How Do They Work? - Tested

This type of filter works for keeping RFI noise off long runs of cable for both analog and digital signals..

I'm a believer in 1-wire sensors. The analog value is changed to digital on-chip then the digital value is sent on it's way. Since you're into Arduino anyway, you can get 1-wire libraries, and most likely differential examples using 1-wire.

-AC

That is a good idea, and I'll probably do that for the solar differential controller I'll be making for my hot water panels. For now, I don't feel like soldering. :) I do want to get some experience with the 1-wire sensors though. They seem to be very nice if you need a bunch of sensors and don't want to eat up a ton of pins on the arduino.

My six 1-wire sensors are actually using 3 wires. Signal, ground and power.
Some of them are on pretty long runs, with odd lengths and they work fine..

The CAI board has the 'reading' firmware build-in. The temperatures/sensor-outputs
just look like data registers to your PLC program. The data is updated in background.
Very easy to use.. This technology is way easier than messing with TC resistors. :)

The attic fan has been going for a little over a week now. Every sunny day giving me some free heat. :)

I'd love to upgrade it to having a 3rd fan. There is still a lot of heat being wasted up there.

I'd also like to add a vent that opens to return house air to the attic so I'm not pressurizing the house when the fans kick on.

I probably won't have time to do either of those mods anytime soon, but just thought I'd share.

I'm also seriously thinking about doing this in my detached garage. It would be used even more since the cooler temps of the garage wouldn't require as warm of attic air.