Forced hot air heaters have filters that need regular cleaning from dust, dander and pet hair. Reggie rubs his head on a filter as his owner vacuums it. Credit: Linda Coan O'Kresik / BDN

Winters in Maine can be difficult enough with freezing temperatures, snow and short days. So furnace troubles are not a problem you want. If you have forced hot air heat, then you should be keeping track of — and regularly changing — air filters.

If your oil, propane or pellet-fueled furnace uses forced air to heat your home, somewhere inside of that furnace is an air filter. Knowing where that filter is, the last time it was inspected and how to properly care for it is important to maintain the efficiency of your furnace.

What are furnace filters?

Think of the filter as the unsung hero of your furnace. Your furnace is constantly pulling in colder air, passing it through heat exchangers to warm it before it travels through ducts back out vents in your home. Along the way the air is picking up dust, dirt, pet hair, dander and other lighter-than-air detritus floating around your house. It’s the filter’s job to prevent those particles from getting re-circulated back into the home or into the rest of the heating system.

“A properly installed and clean air filter is important to the performance of the furnace,” according to Jason Madore, service manager with Daigle Oil Company. “A plugged filter means no airflow, so you won’t get heat going into your house.”

Where is the filter?

The location of the air filter is going to vary depending on the make and model of the furnace. But a good rule of thumb is to start looking for the filter above or in front of the furnace fan. If you have it, check the furnace’s operation manual, which should include the filter’s location. Furnace company websites often have that information available online. When all else fails, according to Madore, it may be time to call in a professional furnace technician.

Inspect your filter

Once you have located the filter, it’s time to remove it and examine it. There are two basic types of filters – those that must be replaced if they are dirty and those that you clean yourself and put back. In either case, if they are dirty to the point of being a dark color or you can’t see through them, it’s time to take action.

If your furnace has a replaceable filter, make sure you have its exact measurements before you buy a new one. Those dimensions should be printed directly on the old filter but if they are not, use a tape measure to determine what size you need.

If your furnace has a filter that you clean and put back in, simply remove it and either blow it clean using compressed air or rinse it out in the sink or shower. Be sure to let it dry before putting it back in. You should plan on doing this at least every three months.

Why bother with the filter?

Keeping tabs on your furnace air filter is among the best ways to maintain the efficiency and extend the lifespan of your furnace, Madore said. As a rule of thumb, filters should be checked and cleaned or replaced every three months.

When air can’t easily pass through your furnace filter, the system has to work harder which could cause it to overheat. Overheating can damage your furnace to the point of needing expensive repairs or even replacement.

If your furnace has to work harder because the filter is dirty, it’s costing your more money to operate. So replacing or cleaning your furnace filter is going to save you money on heating costs.

An efficiently operating air filter’s job is to pull indoor pollutants out of the air. If it is not doing that, you are at risk of breathing in dust, mold, dander or other particles that for some people can cause eye irritation, sneezing, dizziness and respiratory problems.

Furnace filters range in price from $40 to $200 depending on make and model of the furnace itself. But considering that the efficiency of your furnace, not to mention the health of people living in your home, depends on a clean furnace air filter, it can be money well spent.

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Julia Bayly

Julia Bayly is a reporter at the Bangor Daily News with a regular bi-weekly column. Julia has been a freelance travel writer/photographer since 2000.