Know your filters and ductwork to get the most from your furnace

By: Joshua Gordon | Woodward Talk | Published December 16, 2015

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METRO DETROIT — As the temperatures outside continue to drop in Michigan, homeowners across metro Detroit are looking to keep the temperatures inside at comfortable and warm levels.

Much of that work falls on a home’s furnace, but if the furnace isn’t maintained properly, it can result in high energy bills, low heating efficiency and, ultimately, replacing a furnace before the end of its intended life span.

“Generally, most homeowners think that furnaces are bulletproof and they will just run and run and run, but many are not as efficient as they should be,” said Mike Kirin, owner of Total Heating, Cooling & Electrical in Leonard, Michigan. “Furnaces tend to break down when you need them the most in the coldest part of the season, and that is usually due to a lack of maintenance.”

The first and easiest part of maintaining your furnace, Kirin said, is changing the filter. Filters can range from being changed on a monthly basis to being effective for up to three months, depending on the minimum efficiency reporting value, or MERV.

When it comes to filters, however, Kirin said it is a give and take with which kind of filter you decide to buy. While the thicker, higher-MERV filters may collect more dirt, they restrict airflow, he said; lower-MERV filters that allow better airflow may not stop as much dust.

“Some of these filters are so restrictive on airflow that they stop the air from moving, which is critical to the furnace operation and longevity,” he said. “The regular floss-type filters are actually better for the furnace as far as airflow, but worse as far as dust. I lean more to helping airflow, because the restrictive ones can cause the furnace to overheat and damage the heat exchange and put more wear on the unit.”

Tony Contrera, owner of Mr. Furnace in Center Line, added that getting the right filter for your furnace is one of the most important decisions, because getting one that is too thick lowers the efficiency, while filters lower on the MERV rating may not clean the air as much as you want.

“You want a filter that has a minimum of a 4 MERV, which is the efficiency of the filter to catch dirt, but you don’t want to go over 6 MERV,” he said. “Too good of a filter does not make your furnace run any more efficient, but makes it work harder and drives up your electric bill. It is better to change your filter on a regular basis than getting a higher-MERV filter.”

Another key aspect of maintaining a home’s furnace is to have a tuneup at least every two years, Contrera said. A tuneup usually consists of cleaning and adjusting burners for proper combustion to maximize the efficiency of the furnace; tuneups usually cost around $60-$70.

Other yearly checks that Contrera recommended include checking the furnace ignitor as well as the thermostat batteries, which can cause the furnace to appear to not be working when in fact the thermostat isn’t.

Speaking of thermostats, Contrera said that if a homeowner is setting the thermostat down while the occupants aren’t home, it should not be set lower than seven to eight degrees less than the normal temperature.

“If you let your home get too cold, the bricks outside get ice cold and the inside gets cold, and then you have to heat all those parts up again,” he said. “It will take that much longer to warm up the house to retain the heat, and the energy is wasted and the furnace has to work harder. It is best to run at a consistent temperature than to go up or down.”

The time will come, however, when a furnace needs to be replaced. Contrera said furnaces usually last 10-12 years. If a furnace stops running at 90 percent efficiency or above, it probably is time to replace it.

Most new furnaces, he said, run between 92 and 97 percent efficiency, and a new furnace should have better than 95 percent efficiency. Getting a two-stage furnace also is key.

“Two-stage furnaces means the burner burns at a lower BTU ratio if you only want to heat a few degrees, so it is like having two furnaces in one,” he said. “You should also be more concerned with a company’s qualifications when putting in a furnace. Cheapest prices are not always the best value if a one-man operation can’t handle the service, or you can’t count on the dependability of your product.”

Having a furnace properly installed is crucial, Kirin said, as furnaces that are not installed properly can run at a lower efficiency percentage without the homeowner knowing.

And before any new system is installed, Kirin said, the current heating and cooling system at a home should be looked over to see what it can accommodate.

“There is so much new technology out there that a lot of these new furnaces have a higher-efficiency motor for moving air, but if the ductwork is too restrictive, you are not saving any money, but shortening the life of that motor,” he said. “It should be tested to find out what kinds of restrictions your system already has before someone installs a new one.”

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