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.

images of electric room heaters

Risks of Improper Use of Electric Room Heaters

Electric room heaters, or space heaters, have gained popularity in recent years due to rising heating costs and clever marketing ads that claim incredible energy savings by using these heaters. The problem is that many of these heaters are not used as intended which reduces the savings or the electric circuit in the house is not properly rated which can be dangerous.


Proper Use

The intent of room heaters is to add extra heat for individual rooms that you wish to be at a higher temperature than other rooms in your house. For example, if you spend a larger portion of your time in the living or family room, then you may wish for the temperature to be comfortable in that room while allowing the rest of the house to be at a lower temperature to save energy. Another way to think of the intended use of these heaters is as portable zone control, allowing some rooms to be warmer.

The most common misuse of room heaters is using one or more heaters to heat the entire house, replacing a more efficient option of a gas furnace. Electric heat is more efficient at converting energy to heat than other energy sources, however, it is also more expensive. On average, electric heat will cost twice as much as natural gas. Contact us to discuss efficient heating systems to meet your needs.

Additionally, if the room heater is near the thermostat then the main furnace will not function properly. You may need to have the thermostat moved to a more suitable location if you utilize room heaters.


Power Consumption

Contrary to what is stated in the advertising, room heaters consume large amounts of power during use. A quick look at the label on the back or bottom of the unit will provide you with the rated power. Most heaters operate at 120 volts, 60 Hz, 1500 watts. The watts is the power consumed during use and what you are billed for by the utility company.

For information on how electrical energy is calculated, see article How to calculate electric energy cost of common household items.

I’m not saying that these companies are lying to you, but many of the statements are misleading. For example, one ad claims the heater consume the same or less power as a coffee pot. Good deal, right?, because coffee pots don’t use much energy. Wrong! Many coffee pots are rated at 1200 – 1500 watt, which is the same amount of power as the electric heater. However, we don’t think of a coffee pot using energy since it is generally only on for a few minutes each day; whereas the heater will be on for many hours of the day.


Electrical requirements

It is strongly recommend to have an electrician inspect the wiring and circuit protection in your house before buying or plugging in a room heater. The following are areas that David or James will check during an inspection.

1. Available dedicated circuit rated at 20 amps with proper size wiring and breaker (or fuse).

A 20 amp circuit may seem high but keep in mind that a single heater operating at 1500 watts has a current draw of 12.5 amps (1500watt/120volts). Wiring and breakers are sized based on current. It would seem that at 12.5 amps that the 20 amp circuit would still have 7.5 amps available. Unfortunately, that is not the case as breakers and fuses are rated at 80% capacity, which in this case is 16 amps. If any other devices are on the same circuit then overloading of the circuit is likely which will cause the breaker to trip or the fuse to blow.

2. Is the wiring the proper size throughout the entire circuit?

Sometimes different size wiring will be connected together on the same circuit and may cause a larger size breaker to be used where a smaller size is more appropriate (20amp breaker used instead of 15amp). The breaker rating should be sized based on the smallest wire size in the circuit. This is a particularly dangerous situation as the wire size for a portion of the circuit may be undersized and if the circuit amperage is too high for the wire size then the wire may become hot and cause a fire. Unfortunately, this can be difficult to detect in some installation if the wiring is not accessible.

3. Is the wiring in good condition?

Where possible to inspect, the wiring and insulation surrounding the wire will be check for possible damage or degradation.

4. Is the outlet in good condition?

The outlet body and cover plate will be inspected. If broken, then outlet or cover should be replaced. The fit of the plug into the outlet will also be check to ensure a snug fit. As cords are plugged in and unplugged many times over, the outlet socket wears out. A loose fitting outlet will cause the outlet or cord to overheat and damage the outlet and cord plug end. This is a potential fire hazard.

5. Is the outlet 3-prong?

Most heaters use a 3-prong plug which includes the ground connection to carry away harmful electricity in the event of an electrical short inside the heater. The outlet providing power to the heater must be 3-prong and should be grounded back to the service panel. If the outlet is the older 2-prong type then replacement with 3-prong type is required.

6. Do not use 2-prong adapters.

There are serious concerns with using an adapter to convert a 3-prong grounded cord to a 2-prong plugin. First, the heater will not be grounded, see item 5 above. Second, the adapters are not rated for the continuous current that the heaters use and will overheat. Best case the damage is limited to the cord or outlet, worst case is a potential fire.  Third, the two prong adapters do not hold the plug firmly into the outlet. Problems similar to a loose fitting outlet as described in item 4 are likely.

7. Check the cord plug end on used heaters to ensure the prongs and molded rubber are in good condition.

The cord end will be inspected to check for damage due to overheating or bent prongs. The length of the cord will be inspected to check for any nicks or cuts in the insulation. If damaged, then the cord should be replaced.


Manufacturers Warnings

Read manufacturer’s warnings and the provided owner’s manual. Additional information can typically be found on a tag on the cord.

When buying and installing an electric space heater, you should follow these general safety guidelines:

  • Electric heaters should be plugged directly into the wall outlet. No extension cords or power strips.
  • Do not use 2-prong outlet adapters.
  • Buy a unit with a tip-over safety switch, which automatically shuts off the heater if the unit is tipped over.
  • Do not route cords under carpet or rugs.
  • Maintain clear distances recommended by manufacturer.


If you have any question or concerns regarding use of room heaters please contact us.


Thank You,

David McGill
James McGill


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