Why Your Furnace Runs Too Long In Mild Weather

When your furnace operates for extended periods during mild weather, it signals underlying issues that demand attention. Many Ontario homeowners notice their heating systems running longer than expected when outdoor temperatures hover around 10°C. Cycle length can vary by home, but persistent long run times in mild weather are often a sign that something needs attention.

This prolonged operation isn’t just inconvenient—it drives up energy costs and puts unnecessary strain on your system. Understanding why this happens can help you address the problem before it escalates into costly repairs during Ottawa’s harsh winter months.

Thermostat and Airflow Issues

Homeowner OK vs Pro Only

Homeowner-safe steps include replacing the furnace filter, ensuring supply vents and return grilles are open and unobstructed, and checking that the thermostat isn’t near a draft, a sunny window, or a heat source. Pro-only work includes electrical diagnostics, burner or gas adjustments, sealed panel access, combustion testing, and duct modifications or balancing.

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Poor thermostat placement also contributes to extended run times. Units installed near drafty windows, heat sources, or poorly insulated walls receive false temperature readings, triggering unnecessary heating cycles that continue until the device registers the correct temperature.

Quick Checks That Often Explain Long Run Times

If your furnace runs too long in mild weather, start with the basics: a clean filter, clear vents, and a thermostat schedule that doesn’t force frequent big temperature jumps. If you’re using a smart thermostat, confirm it’s not set to an aggressive “recovery” mode or to a frequent schedule that keeps calling for heat.

What a Technician Will Check

A technician will typically verify thermostat accuracy and placement, confirm airflow and static pressure, and look for duct leakage or restrictions that prevent heat from reaching the living space. They can also check whether the furnace is firing and shutting down correctly and whether the system is appropriately matched to the home.

Faulty thermostats rank among the most common culprits behind excessive furnace runtime. When these devices malfunction or lose calibration, they misread indoor temperatures, causing your system to heat continuously even when your home has reached the desired temperature. Older thermostats, particularly common in Ottawa’s heritage homes, are especially prone to these accuracy problems.

Clogged air filters create another significant obstacle to efficient operation. Ottawa’s seasonal pollen and dust accumulation can quickly block filters, restricting airflow throughout your system. When air can’t circulate properly, your furnace compensates by running longer cycles to distribute heat effectively. This problem becomes particularly noticeable during mild weather when your system should operate in short, efficient bursts.

Poor thermostat placement also contributes to extended run times. Units installed near drafty windows, heat sources, or poorly insulated walls receive false temperature readings, triggering unnecessary heating cycles that continue until the device registers the correct temperature.

System Sizing and Ductwork Problems

Oversized furnaces can create a different kind of inefficiency: short cycling. The system heats the home quickly, then shuts off and restarts more often than it should. Even if the total run time isn’t always longer, repeated starts can increase wear, reduce comfort, and make temperature control feel uneven during mild weather.

Ductwork issues compound these problems significantly. Leaks, blockages, or inadequate insulation allow heated air to escape before reaching living areas, forcing your furnace to work harder and longer. Ottawa’s freeze-thaw cycles can damage ductwork over time, creating gaps that worsen during temperature fluctuations.

Blocked vents or closed dampers in unused rooms can also disrupt system balance, causing uneven heating that triggers extended operation. When your furnace can’t distribute air properly, it continues running until all areas reach the thermostat’s set temperature, regardless of how long that takes.

Keep Your Furnace Running Efficiently

Experiencing longer than usual furnace runtimes in Ottawa’s mild weather? It could mean your system needs a thorough check. At Francis Home Environment, we provide furnace maintenance in Ottawa to ensure your heating system operates efficiently. Our skilled technicians can identify any underlying issues, from thermostat malfunctions to ductwork problems. Ask about our heating and cooling maintenance plans in Ottawa for ongoing peace of mind. Don’t let unnecessary heating costs affect you this winter—invest in proper maintenance today and keep your home warm and comfortable all season long!