DIYbanter - View Single Post - Thermostat to turn on fan when it's hot ???

wrote:
I just put a fan in the gable of my barn so my indoor farm animals are
not overheating on hot days. Rather than buying a commercial barn
fan, which is costly and most are too big for my small barn anyhow. I
bought a used fan that is intended to be used as an exhaust fan. I
already had a vent up there, so I just mounted the fan over tbe vent
inside the barn.

However, I dont want this fan running all the time. Only when the
temperature gets about a specific temperature up there at the roof
line. I am assuming it should turn on around 85 degrees. and off at
70 deg.

I have been looking for a way to install a thermostat, but as simply
as possible. To install a standard heating - cooling thermostat like
the types used in a house for furnace and AC, would require a
transformer and quite a bit of wiring. Not that it's out of the
question, but I am thinking there must be an easier way, where the
thing is simply installed in the 120vac line, right next to the fan.
I know they make devices like this for portable and baseboard electric
heaters. But those will be just the opposite of what I want to do.
(it would switch on at the low temp and on at the high - That's
backward). But something similar to that is what I am hoping to find.

Does anyone have any suggestions? I do have an old air conditioner
with a dead compressor. Could something be salvaged from that? I'm
always looking to save a buck if I can salvage something from junk.

Anyone?

Thanks

Mark

First, attic fans with a thermostat cost only
about $30 at the cheapest but $50 is more normal.
Second, the standard way is to put a thermostat
near the fan and it is set for around 95 which
starts the fan earlier than having the thermostat
near the floor, i.e., it may get up to 90-95
degrees at the top of the building while it is
still only 70 near the floor.

Third, if you really want a thermostat near the
height of the animals you may want to get a
thermostat for a hot water tank. These normally
are set in the 110 to 160 degree range but I've
messed around with them and found they could be
set reliably well below 80 degrees. If you look
around you should be able to find one for free.
So find someone with a bad hot water tank and ask
to remove one or both thermostats since bad
thermostats are seldom the cause of replacing the
tank. Or, just buy one (about $10) And, the
thermostats are intended to operate on 240 volts,
so there is no problem operating them on 120
volts. Just put the thermostat in the hot line,
and put some kind of metal or wood housing around
the thermostat for safety since they are rather
open.