Is My Furnace Overheating?

It might be. A furnace is built to make a lot of heat and hand it off to the air that moves through it. When that air cannot flow properly, heat builds up inside the cabinet, and a safety switch shuts the burners down to protect the equipment. If your furnace keeps turning itself off before the house is warm, overheating is a common reason.

The encouraging part is that most causes are simple and preventable. Here is how to head it off and how to tell when it has already begun.

Start with the filter

Filters do the most to keep a furnace healthy or, when neglected, to make it overheat. A filter that is clogged or too thick for the return slot restricts the flow of air, and the furnace heats up because there is not enough air to carry the heat away.

Check the size printed on the frame and match it exactly. Replace a 1 inch filter every one to three months, and look at it monthly through the winter. Dusty homes and homes with pets need more frequent changes. It takes about a minute and it is the single most useful thing you can do.

Keep the air paths open

Supply registers and return grilles have to stay open. It is tempting to close vents in unused rooms, or to push a couch against a return, but every blocked opening raises pressure in the duct system and reduces the air passing across the heat exchanger. Walk through the house and make sure nothing is covering a vent or grille. Ductwork itself can also become crushed, disconnected or packed with dust, and that is something a technician can look at.

Return air matters as much as supply air. A furnace can only push out as much warm air as it can pull in, so a return grille that is partly covered by a rug or a stack of boxes can cause the same trouble as a dirty filter. If you have added a room or finished a basement, mention it at your next service visit, since the duct layout may not match what the furnace was sized for.

Book a professional check

A dirty burner, a failing blower motor or a worn component can all cause overheating. A technician can inspect those parts, test the safety switches and confirm the airflow is right for the equipment. A yearly visit in the fall is the easiest way to keep small faults from becoming winter breakdowns.

Signs your furnace may be overheating

The clearest sign is a furnace that starts a heating cycle and then shuts down before finishing. It may turn on again a few minutes later and repeat the pattern, which wears the parts and leaves rooms cold.

A hot or burning smell is another. A brief dusty smell on the first cold day of the season is normal, since dust burns off the heat exchanger. A smell that persists, or smells like something scorching, is not normal. An unusual humming or buzzing can point to a struggling blower motor, which makes airflow worse and heat build-up more likely.

If you ever smell gas, leave the house and call your gas utility or emergency services from outside. Do not try to find the source yourself.

What to do next

Turn the thermostat down, replace the filter if it is dirty, and make sure the vents are open. If the furnace keeps shutting off, leave it off and call a licensed technician. Repeatedly resetting a furnace that has tripped a safety control is a bad idea, and gas and combustion components are never a do-it-yourself repair.

Air-Tech works on every brand of furnace from our home base at 325 N Oregon Ave in Pasco. If yours is shutting down early, call (509) 392-2021 and we will help you work out the next step.