Should I Turn My Furnace Off Over The Summer?

It's instinctive to turn off your winter heating system when summer comes, not only for your comfort levels but also to save money on those heating oil bills. But is it really the right thing to do? The answer to this will depend on where you live and what type of heating system you have.

What type of furnace do you have?

In the United States, there are two commonly used oil-fired heating systems. Both have an oil tank and delivery system, with a thermostat control and a flue pipe to disperse combusted material to your chimney. Mostly the heat generated is delivered via a forced-air system where vents in the walls or floor deliver warm air to your home. Less common nowadays is to use water or steam from a boiler to supply radiators, underfloor radiant heating or baseboard heaters.

Why do oil-fired furnaces still run in the summer?

Your furnace may continue to burn oil during the summer months because:

  • it's an older model with a pilot light;

  • it's supplying a boiler to heat water;

  • it's running your A/C.

Traditional, older-style (more than 15 years old) furnaces use a pilot light that never goes out but continues to burn a little of your heating oil. You can't turn the pilot light off if your furnace is using a boiler because not only might your hot water supply dry up but the metal in the boiler will shrink as it cools down. This can lead to cracks in the metal, and ultimately damage your whole heating system.

The pilot light ignition system saved time starting the furnace manually, but is very inefficient in heat production and wastes heating oil. Modern furnaces have become more efficient in fuel use. This is due to changes in hardware that reduces combustion losses and replaces the pilot light with electronic ignition.

If your boiler is functioning as a water heater, using tankless coils to heat the water, then it needs to be hot. In the winter that's not a problem, but in the summer the system works overtime switching your boiler on and off whenever you need hot water. Doing this could reduce your boiler’s fuel efficiency all the way down to 25%, gobbling up as much as 300 gallons of precious heating oil in the summer months.

If you have central A/C, your furnace will need to be on to power the system in the summer (using a compressor and evaporator coil). Turning off your furnace is therefore not an option if you need A/C to keep cool.

So, should you turn off your furnace for the summer?

There's no 'right' answer to this question, but it depends on weighing the risks against the benefits for your particular heating system. Think carefully before you take any action, to avoid problems in the future. Better still, consult a local heating oil dealer or ask an A/C technician for professional advice.

If you do decide to turn off your furnace, your savings may include $2 to $4 a month in the energy used to keep the pilot light going. You may also gain potential savings of $300 to $500 over the summer from the 200 or 300 gallons of heating oil you'd be using up to keep your boiler running.

The risks of switching off include corrosion in your furnace from a buildup of soot and/or condensation, plus debris and contaminants accumulating in your oil tank if it's not active. As well as bacteria and fungi, you may well find insects and spiders making themselves at home. This might block the oil supply and require you to drain and clean your storage tank.

If you do shut down your furnace, you should clean and dust it after you turn it off to prevent any accumulated burned dust particles or allergens from being dispersed inside your home through the forced-air heating system. Dust may also collect in the air filter, so you should replace the air filter in your furnace once or twice every year.

Preventative maintenance

Year-round maintenance is key to improving the efficiency of your furnace and extending its useful life. You can also improve its long-term energy-efficiency by scheduling an annual inspection and clean by a professional technician, regardless of whether you turn your furnace off for the summer.

Make sure to inspect the furnace yourself for rust or soot buildup, which can be indicated by dark chimney smoke when you fire it up. Also, fill up your oil tank before closing down your furnace and include a special additive to help prevent contamination and sludge.

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