How to insulate a thermostat

Question

Some previous owner of my home moved the original round 2-wire thermostat to a wall of the vertical chase used for the hot water heater vent, the gas lines, etc. The wall is quite a bit colder than normal interior walls, which I assume is because the chase is at least partly open to the attic (which has blown insulation).

My heater tends to stay on for long periods and off for short periods, and I'm trying to control the reasons as best I can (which includes repairing drafts, etc.).

Is that chase wall affecting the modern thermostat? If so, what could I use as an insulator between the thermostat and the wall to ameliorate the effect? Regrettably, moving the thermostat isn't a trivial option.

After five years I can't clearly remember if we had problems with the original 2-wire thermostat. But I believe we didn't. The problems arrived with the modern thermostat....

Answer 1

If you really care, you can replace the thermostat with an ecobee (or other similar electronic thermostat). With luck you will have a C wire, otherwise you can power it externally. (e.g. see this answer https://www.reddit.com/r/ecobee/comments/fpj57f/wiring_a_power_supply_for_my_ecobee_3_lite_which/)

Now the purpose of this is to allow you to use a remote sensor. This is an electronic thermometer roughly the size of an ice cube. You can put it wherever you want, but not on your cold wall. You can also instruct the electronic thermostat to have minimum or cycle times, or a minimum cool-off time.

In my experience, having a cold wall or having the thermostat in a cold area results in the space being overheated. A furnace running at nearly 100% duty cycle, however, indicates that your furnace is too small -- does it struggle to keep the house warm on very cold windy days?

Now if you would like a cheaper way to test this, drill a small hole in the drywall and insert the straw of one or more cans of expanding foam into the cavity behind the thermostat, building up a large insulated area behind it. This should also show that the temp of the wall rarely makes a difference.

Answer 2

Here is a possible way to test the idea that the wall is influencing the thermostat:

Take the thermostat off the wall, temporarily extend the low-voltage thermostat wires with a bit of cable of suitable conductor count and jury-rigged up out of the way of passersby, and put the thermostat somewhere else in the same room for a time. Try different places for a few tests.

If the activity of the HVAC system changes, then it could be the wall's influence on the air in the area in front of the wall.

If the temporary thermostat move does change the HVAC behavior positively, I would try insulation batts inside the pipe chase behind the wall surface that holds the thermostat. Rock wool batts might hold up relatively by itself with a few screws through it.

Answer 3

Spray foam and/or loose fill insulation the wall bay full. This will stop any draft. Honestly though, if the rest of the house is properly insulated then an interior wall has no need of insulation.