Friday, April 6, 2012

Project: Thermostat Upgrade

For the last four years, I’ve been full-timing in my camper.   For the majority of that four years, my camper’s furnace has been controlled via the original factory thermostat.


I learned really fast in my first winter full-timing that it wasn’t the best of thermostats by design when the furnace started to run constantly because the temperature pickup coil would be affected by the, at the time, un-insulated fridge compartment.  

My fix that winter was to cut a piece of Reflectix, wrap it in duct tape and install it behind the thermostat.

It’s performance improved more with the remodel of the fridge compartment to fill all the dead air space around the fridge with insulation so that it was no longer affected by the outside temps, but it still was a pain in the butt to set accurately, but I lived with it.

I bought a replacement, sometime before the Fall Colors Rally of 2011, but didn’t get around to installing it till April. 

For a replacement, I bought a programmable digital thermostat, a Honeywell RTH221B 1 week thermostat.


I picked this particular model because it was designed for fairly wide range of heating and cooling applications, including millivolt use.  My old Suburban furnace uses a very basic 12volt circuit loop to switch the unit on and off, so all the thermostat really does is complete the power circuit, so this thermostat was a perfect replacement.

Other advantages including being able to program a lower temp during times of the day, and have it automatically adjust, or simply set it to hold a specific temperature which can be adjusted up and down in 1 degree increments.

Fortunately for me, the previous owner used the correct color coded wiring for a thermostat for house systems when he did the furnace upgrade, so it was simply a matter of matching up the wire colors to their specific terminals on the backing plate.


The thermostat is designed to work with heating and cooling, so if you have a roof top A/C that can be run by a remote thermostat, this will work for that as well, however, it doesn’t have a fan speed control, simply a fan ON or Auto option. 

That was pretty much all the wiring, the actual thermostat is removable so that you can change the two AAA batteries it uses. 

There’s one tiny Phillips screw on the top that secures it in place and that’s pretty much it for installation.


One thing I dearly love about this particular model of thermostat is while you can’t set a specific number of degrees you want it to wait between cycles, you CAN set how many times an hour the furnace can cycle, the slowest being once every half hour will it check to see if it needs to cycle on. 

I have mine set to once every 20 minutes, which keeps the camper temperature even without too wide a range of temperature swing, and at the same time keeping the runtime to a minimum so that the batteries don’t get drawn down too far.

So, there you have my super simple and quick thermostat upgrade.