Thermostat war–Is your room heater fighting with your furnace? Who wins?

Perhaps the better question to ask instead of Who wins? is Who loses? You do. When the furnace and room heater are working against each other, you pay more in heating cost.

To get the furnace and room heaters to work together–and save you money–the thermostat for the furnace cannot be in the same area as the room heaters. The two thermostats will fight with each other and whichever one is set to the higher temperature wins; hint, this is usually the room heater which will cost you more money.

Room heaters may save you money if used correctly. The best use of a room heater is to increase the temperature of the rooms that you use most often to allow the furnace thermostat to be set lower, reducing how often it runs. For example, the furnace can be set to 65 degrees to keep the house at a minimum level and the room heaters can increase the temperature to 68-70 degrees for those individual rooms.  This is great in theory but will be difficult to achieve if your furnace and room heaters are not playing nice with each other.

First let’s talk about your thermostat, because that is what tells the furnace when to turn on or off based on your desired temperature. For furnaces, the thermostat is usually mounted on the wall in one of the primary rooms and can be set to a temperature, such as 68 degrees. For room heaters, the thermostat is built into the unit and may include a display for the temperature setting or simply have a dial or buttons to increase or decrease the temperature.

Scenario #1 – Your furnace thermostat is in the same room as your room heater.

You set the furnace thermostat to 65 degrees. Say you want the living room to be nice and cozy at 70 degrees so you crank up your room heater. Ahhh!  Only now the furnace temperature setting is lower than the temperature of the room and will not turn on, allowing the rest of the house to get cold. Then what happens is the heat from the warm room will carry into adjacent rooms in the house and will try to heat those rooms as well. This causes the room heaters to run more and reduces the money savings.

Scenario #2 – Your furnace thermostat is away from your room heaters.

You again set the furnace thermostat to 65 degrees and use your room heater in the living room to make that room nice and cozy at 70 degree. Because the furnace thermostat is in a separate room, not heated by the room heater, the furnace will turn on when the temperature falls below 65 degrees. The two heaters are working together, providing you with comfort and money savings.


If your scenario is similar to #1 then you may need to consider the following options.

1. Relocate the furnace thermostat to a better location that allows the room heater and the furnace to work together.

  • Keep in mind that during the summer months the furnace thermostat controls the AC and the current location may work well for cooling.
  • Moving the thermostat may leave a hole in the wall that will need repaired.
  • If moving the thermostat is not practical then consider installing a second thermostat at the desired location. The old thermostat can be abandoned or used during summer months only. (Only one thermostat can be connected to the furnace so you will need to have a qualified electrician switch the thermostat wiring at start of each season.)

2. If the room heater is only used temporarily, say only when you have company over, then you may be okay with leaving the thermostat in that room. If the rest of the house gets too cold then you could turn up the furnace thermostat until the furnace turns on and let it run for a few minutes and then turn the thermostat back down.

Note: Installing or rewiring a thermostat requires an understanding of electrical circuits and is best done by qualified electrician.

Call us at 641-437-1086; we are here to help you.


Thank You,

David McGill
James McGill


Article written by Tim McGill, editor @ Tree Branch Publishing.

Posted in Energy Savings, Heating and tagged , , .

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