With the escalating prices of home heating in recent years, many people have begun to make use of a combination wood and oil furnace. This type of furnace gives the homeowner flexibility in what they heat their home with during the cold winter months.

Wood furnaces can be installed to work in conjunction with systems using other fuels such as oil, natural gas and electricity. Combination wood-oil furnaces can use both energy sources in a single packaged unit.  Add-on furnaces can be installed beside existing furnaces using other fuels. All such units must be safety tested and certified for this purpose.

Just like any other furnace, a central heating system uses a network of air ducts to distribute heat to all rooms of the house. Furnaces heat air, which is forced through ducts with a fan.  Central heating with wood-fired furnaces is not as common as it once was. Part of the reason is that houses are more energy efficient and easier to heat with stoves and fireplaces that also provide a view of the fire.

Another reason is that advanced technologies were not used in furnaces until recently so their efficiency was low. Even today, only a few central wood burning systems have proven advanced technologies. Central heating with wood may be a good option for your house if:

  • the house is old, large and not very energy efficient
  • the house is made up of many small rooms with no large open areas
  • there is no suitable place to install a fireplace or wood stove
  • fire viewing is not a high priority
  • or you wish to confine wood fuel to the basement area

Sometimes it’s just great having the best of both worlds.  It is nice to have the option of burning wood when it’s convenient but it’s also nice to have the ability to go away, or have your heat last throughout the cold winter nights with the oil fuel and that is where these combination furnaces really shine.

While this is a great way to keep some heating costs down, there are some potential problems associated with a combination wood and oil furnace.

Chimney Requirements

For anyone who is looking into purchasing, or installing, a combination wood and oil burning furnace, they will want to pay very close attention to the chimney requirements. Since you are burning two different types of combustibles, they have their own flue, draft, and cleaning requirements. The technical specs on the type of furnace you buy will determine the specific needs. However, most of the time there are different flues for both of the heating services to work.

Space Requirements

After making sure that the chimney is going to be adequate for your furnace, the next most important thing to look at is the space where the furnace will go. The oil burning side of the furnace is not going to require much space.  Many times they can be closed in very tight quarters.  Wood stoves and furnaces, however, must have plenty of space as they can rise to extreme temperatures.  Installing a combination furnace will require at least 3 to 6 feet of clearance around the furnace to protect the home from fire.

Cleaning Requirements

An oil burning furnace will require an annual cleaning to ensure that is runs efficiently and without any problems. The wood burning furnace must be cleaned every day.  As wood is burned, there are two things that accumulate within the burn chamber. First, you will have the ash.  This must be removed to keep the air circulation at its most efficient. The second particle is creosote. This is not as much of a problem if you are burning processed materials such as wood pellets.  Creosote can build up very quickly, especially when the weather is very cold and then turns warm. This excess build up will cause smoke to go throughout the home instead of out the chimney.

Air Flow

When you burn wood you must have an adequate air flow into the burn chamber so that the wood will burn at the right speed.  If you mostly use the oil furnace and then switch to using wood, many homeowners forget to check their air damper on the chimney.  This will cause the smoke to be blown back into the home, or the wood to burn inefficiently.

A word of caution about installing a wood burning furnace

When considering central heating with wood, your heating retailer or contractor is your best source of information on available systems and their suitability for your home. Since the installation of central heating appliances is complex and requires several specialized skills, it is recommended that you hire professionals to do the work.

All wood-burning furnaces must be safety-certified in Canada. During testing, the details of installation are determined.  As a result, the installation rules for each central heating furnace can be different and will be found in the manufacturer’s installation instructions. Also, this type of installation is complicated and should be carried out by a trained professional.

How much does a wood/oil combination furnace cost?

Prices can vary by retailer so check with your local professional for an estimate.  That being said, the average cost of a combo wood/oil furnace is in the $3000-$5000 range plus an additional $1200-$1500 for installation.

*Schematics courtesy of Carson Dunlop