Additional Heat
One furnace is often not adequate when heating a large house or office building. A second furnace allows you to add more heat into the home without overextending your existing furnace. Heat disperses through a space, so a large house is likely to still have drafty areas with a single furnace. A second furnace gives you added control over how warm you want your house to be, and makes your home more comfortable during times of extreme cold.
Backup in Emergencies
A malfunctioning furnace can be lethal in locations that have dangerously cold temperatures during the winter. Older people, children and people with medical conditions are more susceptible to the dangerous effects of cold weather. A non-working furnace can make their homes unlivable as a result. A malfunctioning furnace may also spew dangerous levels of carbon monoxide and other gases, and people may run the furnace anyway if it is their only source of heat. A second furnace eliminates this risk because you have a second furnace that keeps you warm while you wait for the first one to be fixed.
House Heats Evenly
A furnace in the basement of the home is likely to warm the basement and lower levels of the home while leaving the upper levels and attic chilly, even with a duct system in place. Another furnace located in a different part of the house helps prevent this problem and ensures that the building is heated evenly. This keeps the house comfortable no matter where you are, and this keeps you from avoiding certain rooms during the winter because of the uncomfortable cold.
Reduces Wear and Tear
Running a furnace on its highest setting over an extended period of time is more likely to result in maintenance needs and furnace damage. Conversely, running two furnaces on a lower setting gives you an equal amount of heat without the added wear and tear on the heating system. Either run them both simultaneously at lower settings, or alternate between one and the other on a higher setting. The furnaces are likely to last longer because of the reduced activity of each system.