would this work?

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OHIOSTEVE

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I have almost finished a small walk in ferment room. I am trying to figure the best way to control temp. I know I can buy a 2 stage controller BUT wouldn't this work as well since it will need heated and cooled sometimes both in the same day right now. Set a small AC with a digital thermostat in the wall and set the thermo to 64 degrees. Then set a small space heater with a digital thermostat set to say 60 degrees. When the temp gets above 64 the AC would kick on.....and then kick back off at 64. if the temp dropped below 60 the heater would kick on and then back off at 60. The AC I plan to use has a setting that turns it completely off once temp is reached but it has a much wider temp range before restarting. with the mass of the carboys I don't think this would be an issue . Ok tell me whats wrong with this before I screw up my ferment room.
 
It may work, the problem is your AC and heater aren't as accurate as we'd like to assume and they aren't calibrated to each other (so they may not read the same temperature). Generally what happens with the AC is it will spit out cooling until the thermometer in it hits the set point (in your case 64F). The cold air that is spit out at the end (say the last 5-10 minutes) isn't really accounted for though, so your will probably drop below that. I have a kegerator that is cooled with an AC down to a set point of 40F, but have consistently seen temperatures of 37F. The same will go with the heater but in the opposite direction (the room will heat up a little more even after the heater has shut off).

The other issue is calibration. The AC may register the room at 64F, but the heater may register it at 60F, so they both kick on and fight each other. Again, with my kegerator, I have a Love controller and a second temp sensor. They are almost always off by 1-2F from each other (the sensor reads a little colder) even though the thermometers are literally on top of each other.

So if you have time to experiment, you could probably get your set points correct but for the $30-$50 it would cost to get an ebay temp controller, I'm not sure it's worth it.
 
I'm not sure about your A/C and heater but my window A/C, when set to 70 degrees goes on when I feel hot and does not go off until I feel cold. So I suspect more than 10 degrees total temperature swing.
 
It sounds like a good idea on the surface, but if the room is well insulated, you are not going to have that much of a temperature swing during a single day.
 
It may work, the problem is your AC and heater aren't as accurate as we'd like to assume and they aren't calibrated to each other (so they may not read the same temperature). Generally what happens with the AC is it will spit out cooling until the thermometer in it hits the set point (in your case 64F). The cold air that is spit out at the end (say the last 5-10 minutes) isn't really accounted for though, so your will probably drop below that. I have a kegerator that is cooled with an AC down to a set point of 40F, but have consistently seen temperatures of 37F. The same will go with the heater but in the opposite direction (the room will heat up a little more even after the heater has shut off).

The other issue is calibration. The AC may register the room at 64F, but the heater may register it at 60F, so they both kick on and fight each other. Again, with my kegerator, I have a Love controller and a second temp sensor. They are almost always off by 1-2F from each other (the sensor reads a little colder) even though the thermometers are literally on top of each other.

So if you have time to experiment, you could probably get your set points correct but for the $30-$50 it would cost to get an ebay temp controller, I'm not sure it's worth it.

I'll just echo the above statement. Too much room for error if you don't have both devices plugged in to the same temp controller.
 
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