I don't want to get up at 2am to change the thermostat...

June 2, 2007 6:47 PM

Can someone help me find a thermostat without a manual heat/cool selection switch?

I want to set a temperature on my thermostat, and have it automatically engage the heat or cooling system to keep the house within a few degrees of this temp.

All the thermostats that I can find have a manual or digital switch to be set to run either the heating system or cooling system, so if the temp starts rising or falling, you need to manually switch it to the cool or heat setting.

I need to keep the ambient temperature stable for several aquariums that I have, and sometimes in the fall and winter, it's a pain to switch the system back and forth depending on time of day and if it's cooler or warmer than usual. Why can't the thermostat just get a temperature range (let's say 21 to 23 degrees Celsius) and engage the system it needs to run?

If it matters, I have forced air heating via a natural gas furnace, and central A/C.

posted by WinnipegDragon to home & garden (6 comments total)

I have a honeywell one I found on ebay. You are probably having a hard time at places like home depot, lowes as this feature is more of a commercial thing -- not sure why.

The feature is called auto changover or auto switchover.
posted by thilmony at 7:07 PM on June 2, 2007

I found mine... here it is:

http://www.honeywell-thermostat.com/honeywell/t8602-thermostat.htm
posted by thilmony at 7:09 PM on June 2, 2007

Because of the latency in actually heating and cooling your home and because the only control of the heated/cooled air is whether it's on or off (not its temperature, not the rate of forced air), a simple thermostat doing what you want will start "fighting" itself when the temperature is close to its setting.

However, a more sophisticated thermostat (meaning one that uses an intelligent algorithm for controlling the heating and cooling units) like thilmony recommends will manage this.

Another thing you could do is buy two identical cheap thermostats to replace the one you have. Attach one to the heater and one to the cooler. You could try setting both to the exact same temperature to get an idea of why doing so won't work very well. But what would probably work would be to set the two thermostats to bracket the temperature you're aiming for. For example, set the heater to 21C and set the cooler to 23C.
posted by Ethereal Bligh at 7:09 PM on June 2, 2007

Yeah Home Depot just hasn't been able to help me with this.

I'll try and find that Honeywell one online!
posted by WinnipegDragon at 7:17 PM on June 2, 2007

My house came with one like this, it's pretty cool, though it feels wasteful when I set it to run the heater below 70 and the air conditioner above 74.

Also, I've found in the Pacific Northwest at least, there are rarely cold nights and hot days in the same 24 hr period.
posted by mathowie at 7:53 PM on June 2, 2007

yes, while the auto feature is cool, in the Minnesota spring and fall it seems weird to have the AC kickin on monday and the heat on tuesday. often in the fall i set it to AC only, and the spring heat only.
posted by thilmony at 8:19 PM on June 2, 2007