attic fan thermostat / temperature control suggestion

[Poppy]

Please let me preface this request for information from a group of flashlight geeks, but I have often been amazed at the depth of knowledge on an amazing variety of subjects, the membership here holds.

I have a attic fan. It has a 36 inch box, and I suppose a 30 inch three bladed fan. It can move a LOT of air. I imagine that it should be able to move enough air to give the attic a complete change of air in about 15 minutes, yet it runs for hours at a time.

I am using this as a thermostat.

It is supposed to start the fan at the temp it is set at, and turn the fan off when the temp is 7-8 degrees less.

A couple of nights ago, it didn't turn the fan off until 3:30 AM.
The fan's drone is loud enough that I heard it go off. It does impair my sleep.

Here's the question:
Is there a programmable thermostat, that will not only monitor the ambient temperature but also the outside temp? one problem may be that the outside temp may be above the OFF temp of the fan. If so, the fan will run all night long. This will not only keep me awake, but it will have additional energy costs.

 

[raggie33]

damn idiot roofers not only took off my attic fan they covered the hole

 

[xxo]

Can you switch it off when you go to bed?

 

[Poppy]

Can you switch it off when you go to bed?

I have done that by throwing the breaker, but that also turns off the living room outlets. I did that last night before going to bed.

I just went up into the attic and found that the middle height air was the same as the outside air, or within a degree or two. I adjusted the thermostat to a higher temp, by a degree or two, and it turned off the fan.

I'll sleep well tonight.

 

[turbodog]

In no particular order...

1) Unit could be failing... contacts could be welding together due to use/age. You can turn off power, disassemble, and try to inspect/sand/clean/etc the contact points.

2) Unit could be seeing radiant heat from the roof decking which would influence its accuracy. Not sure _why_ this would have changed recently, but you cold relocate the unit or shield it from radiant heat from the decking with a tin pie plate or something reflective.

3) I misread your outside air temp concern... yes, that could be influencing the reading and causing it to run long. I would remount the unit down low, far away from the roof, and that will probably work well enough.

4) What temp is it set for currently? Raise the temp 5 degree and see what happens.

 

[Chauncey Gardiner]

Searching the net I read the thermostat should be set to around 100 / 110 degrees. Wondering if yours is set to a cooler temperature, or if not, perhaps your thermostat is faulty.

 

[aznsx]

I have done that by throwing the breaker, but that also turns off the living room outlets. I did that last night before going to bed.

I just went up into the attic and found that the middle height air was the same as the outside air, or within a degree or two. I adjusted the thermostat to a higher temp, by a degree or two, and it turned off the fan.

I'll sleep well tonight.

Yeah, an incrementally higher 'setpoint' setting is / was the best 'first thing' to try, before fundamentally altering the setup / equipment. If that doesn't do it, then escalate technically as needed.

 

[Poppy]

TurboDog, and Chance, once again you have proven that there is a great depth of knowledge here!

The thermostat is less than 2 years old. But $$$$ happens and I replaced it with a new one. No solution to the problem. So I read the installation instructions! Will wonders never cease? One is NOT to obstruct an air vent hole that shall allow air to surround the thermistor. I think they are referring to a 1/8 x 1/4 inch hole in the back of the unit, that would naturally be blocked if one positioned the thermostat against a stud or joist. To be sure that there is maximum airflow, I removed the cover, I also made sure that the little hole was unblocked.

I have read that it should be set at 90 to 110. I selected 95F.

Tonight, I turned the selector until it turned off while the thermometer read at 80F. IT didn't take much, it was really close to shutting off.

IDK, Just leaving the unit at a higher turn on setting may alleviate my sleeping issues, MOST nights, but now that I am on an information quest, shouldn't there be a thermostat that takes into account of the outside temperature?

 

[Chauncey Gardiner]

TurboDog, and Chance, once again you have proven that there is a great depth of knowledge here!

The thermostat is less than 2 years old. But $$$$ happens and I replaced it with a new one. No solution to the problem. So I read the installation instructions! Will wonders never cease? One is NOT to obstruct an air vent hole that shall allow air to surround the thermistor. I think they are referring to a 1/8 x 1/4 inch hole in the back of the unit, that would naturally be blocked if one positioned the thermostat against a stud or joist. To be sure that there is maximum airflow, I removed the cover, I also made sure that the little hole was unblocked.

I have read that it should be set at 90 to 110. I selected 95F.

Tonight, I turned the selector until it turned off while the thermometer read at 80F. IT didn't take much, it was really close to shutting off.

IDK, Just leaving the unit at a higher turn on setting may alleviate my sleeping issues, MOST nights, but now that I am on an information quest, shouldn't there be a thermostat that takes into account of the outside temperature?

I think what you're looking for is called a fresh-air intake thermostat or a make-up air thermostat. One of our school buildings has two tandem furnaces. Each tandem unit is equipped with a natural gas preheater. The temperature of the make-up air entering the preheater determines when the preheaters are activated.

 

[turbodog]

...obstruct an air vent hole that shall allow air to surround the thermistor...

If a thermistor is involved then I _highly_ doubt there are contact points. Sounds like an all solid-state device, no mechanical parts inside.

And an attic at 95-100F? Sounds very cold... probably unattainable. My fan is set at 120F. Keeps it decent... used to be ~140 before it was installed.

 

[bykfixer]

One thing to note also is if you have stuff in the attic like the fake Christmas tree, your winter clothes, an old ironing board you never use……you know, stuff……well that stuff holds heat. When the attic is cooling the cabin air temp might be down to 90 but the stuff is still radiating heat.

 

[Poppy]

If a thermistor is involved then I _highly_ doubt there are contact points. Sounds like an all solid-state device, no mechanical parts inside.

And an attic at 95-100F? Sounds very cold... probably unattainable. My fan is set at 120F. Keeps it decent... used to be ~140 before it was installed.

I misspoke. It does have contact points, so I guess it is a bimetal doohickey.

I re-read the installation instructions and it says to set it to 105 degrees. Also that it will turn off at about 7-8 degrees cooler. (97-98) degrees. At that hot, I won't be sucking in outside air that is hotter than the air inside the attic, at any time. Therefore, I won't need to worry about the outside air temp.

Thanks for the suggestion Chance.

Yes Mr. Fixer, the attic is full of stuff. A huge heat sink! I suppose that it is possible that if the outside air temp drops rapidly enough, that the fan can replace the hot air in the attic quickly enough that it will shut down, and the stored heat in all that stuff could possibly heat the attic enough to turn the fan back on. So it is possible that it might cycle on and off a couple of times.

 

[turbodog]

To dig deeper... safe attic temp would depend on what's up there. From what I was told, the 140 mine used to be was too hot... would cause shingle degradation.

Also, my HVAC is up there... so not doing it any favors either. Dropping the temp helped avoid a blast of hot air when the unit turned on.

Water heaters are up there also. Summertime temps help keep them toasty. Guess I could run some loops of copper pipe to preheat incoming water, or get a dummy tank to use for preheating.

It's set at 120 now... and honestly it will run well past dark before it cuts off in summer.

 

[Chauncey Gardiner]

It wasn't a suggestion, Poppy. I was only trying to answer your question. Attics are terrible places to store stuff ...... most of us do it.

 

[bykfixer]

If attics have proper ventalation the temp will likely be a lot lower in summer. Trouble is most do not.
My parents 2 story house has a small vent at the peak of each end and 8 small inlets near ground level and relys on airflow between the insulated walls to vent the attic.

My house has a horizontal vent every 4 feet apart under a soffit and 2 large vents at the peak. If not for all of the stuff interupting airflow it would probably be much cooler in summer.

Last year I had a shed brought in and the thermometer inside at times would read 120+ degrees. Storing gasoline in there that temperature had me a little nervous. I driiled several half inch holes at the peak of one end and keep the one window open on the opposite end and it now stays 10-20 degrees cooler without a fan depending on outside air temps. I looked into installing a solar fan but found the siphon effect was good enough.

 

[Poppy]

If attics have proper ventalation the temp will likely be a lot lower in summer. Trouble is most do not.
My parents 2 story house has a small vent at the peak of each end and 8 small inlets near ground level and relys on airflow between the insulated walls to vent the attic.

My house has a horizontal vent every 4 feet apart under a soffit and 2 large vents at the peak. If not for all of the stuff interupting airflow it would probably be much cooler in summer.

Last year I had a shed brought in and the thermometer inside at times would read 120+ degrees. Storing gasoline in there that temperature had me a little nervous. I driiled several half inch holes at the peak of one end and keep the one window open on the opposite end and it now stays 10-20 degrees cooler without a fan depending on outside air temps. I looked into installing a solar fan but found the siphon effect was good enough.

On a previous house, I had to replace the roof. When we did that, my brother told me, to bring it to code we needed to install a ridge vent. Between that, and the soffit vents, we didn't need a power vent.

At this house, there are two 12x12" vents at the peak, and no soffit vents to speak of, and this 36 inch fan. Fortunately there are a couple of screened windows that we open in the summer.

The previous owner lived here for four years, and all that time, the fan didn't work. We moved in during a week of 95+ heat. The first thing I fixed, was that fan.