Electric Furnace Overheating: Causes And Prevention

Construction & Contractors Articles

Electric furnaces are often used by homeowners who don't have access to oil or natural gas, and their relatively simplicity makes them a popular, low cost alternative for even those who do. Electric furnaces are inherently safer than fossil fuel furnaces since they don't use open flames or produce potentially-deadly combustion byproducts such as carbon monoxide. However, there is one area that cause trouble for homeowners: electrical overheating. Below are some reasons why electric furnaces overheat and what you can do to prevent it from happening:

How an electric furnace operates and overheats

Electric furnaces use high-amperage, high-voltage electricity to heat elements, which usually consist of coiled nichrome wire. A fan blows across these heated elements and distributes warm air through the ducts and into the home.

Inside the furnace itself are several potential "choke points" where electrical overheating can arise:

Sequencer

This device consists of one or more low-voltage electric switches that transmit electrical power to the heating elements; they activate in stages so the furnace doesn't place a sudden power demand upon electrical components. Sequencers also control the operation of the fan so it is timed to come-on and turn-off at the correct time.

If the sequencer fails and it causes the fan to turn on too late or shut down too early, the elements will overheat due to insufficient ventilation. This will cause them to break at particular hot spots, such as where the elements are supported by ceramic insulators, or repeatedly trigger the limit switches.

Limit switches

Limit switches are safety mechanisms designed to automatically shut down the flow of current as it passes through the heating elements. Limit switches operate using a special sensor, and they cut power to the elements when activated.

Limit switches are not designed for frequent on-and-off operation. Repetitive operation will cause internal mechanical failure and can overheat sensitive limit switches. If a limit switch fails entirely, it can prevent the elements from turning off which might in turn lead to a fire.

Wire terminal connections

These consist of the numerous wiring connections to various internal components, including the sequencer and limit switches. Most wire terminal connectors within electric furnaces are blade connectors; these connectors simply push and pull apart for connection and disconnection.

Blade connectors are easy to use, but they can frequently become loose. Loose connections are a cause for arcing and this can result in wire overheating and melted insulation.

How to prevent electrical overheating inside a furnace

There are several ways you can prevent your electrical furnace from overheating. Below are some tips and hints:

  • Frequently replace air filters – dirty or clogged air filters can prevent air from properly circulating through the heating elements and lead to overheating. Replace filters at least once per month during periods of high use.

  • Replace sequencers at the first sign of trouble – if your electric furnace fan doesn't turn on when the heating elements first begin warming, or if you notice the fan stops too soon, then you sequencer may need replacing.

  • Inspect and replace limit switches – defective limit switches cause inefficient cycling of your furnace as well as putting strain on your system. Be sure to check and replace your furnace limit switches if the furnace begins to cycle on-an-off too quickly.

  • Tighten or replace blade connectors – blade connectors can usually be tightened with by carefully using a pair of pliers. Gently squeeze the connectors so they can still slide together but fit snugly. If the blade connectors on your furnace seem to be past the point of furnace repair, then you should cut the old ones off and attach new ones to the end of the wiring. Just be sure there is a sufficient length of wire available to work with, or you will need to remove the entire section of wire and replace it.

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7 April 2015

Exploring Contractor's Hand Tools

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