If your furnace is more than 20 years old, you should upgrade to a high efficiency model. You should also consider switching if you have an old burner that was converted to oil or gas. You may think about a new furnace if you have a gas model installed prior to 1992 where it has a pilot light rather than an electronic ignition. Pilot lights waste energy because they are always burning whereas electronic ignitions activate only when the furnace is engaged.
How Forced Air Furnaces Work
Air from inside the house is drawn into the furnace through cold air ducts, then warmed and delivered back through hot air vents. When the cold air is drawn back, the furnace filters out dust and other particles found in the air. Gas and oil furnaces have a pilot light that warms a heat exchange unit and a flue for exhausting the gases to the outdoors. Electric furnaces use elements or heating strips to warm the air. Coal or wood furnaces have a sealed firebox where the fuel is burned and a heat exchanger warms the incoming air.
How High Efficiency Furnaces Work
These furnaces have an additional heat exchanger that takes the hot exhaust gases and extracts any available heat before it is sent outdoors. A high efficiency condensing furnace takes this extracted heat and condenses it into water and drains it. The remaining cool gases are exhausted to the outdoors. By doing this, there is no hot air escaping from your home. In addition, the venting can be done with a PVC pipe rather than up a heat resistant flue in the roof. It also reduces the amount of pollutants released into the air.
How Mid-Efficiency Furnaces Work
These furnaces do not condense the extracted heat; therefore do not require drainage. They have a power exhaust and no draft hood. As a result, more heat is exchanged. A heat resistant vent or an existing flue must be used. This is ideal for houses where new venting and/or drains cannot be installed.
Rating for Furnace Efficiency
All furnaces are rated for efficiency and the measurement is called the Annual Fuel Utilization Efficiency (AFUE) rating. This measurement is based on how much energy is converted to heat and how much is exhausted with the gasses that go outdoors. An AFUE of 80 means that 80% of the fuel is used to warm your home and 20% is exhausted. High efficiency furnaces register an AFUE of 90% or better. Mid efficiency have a rating of 78% to 89%. Gas furnaces are the most efficient and some can achieve a rating of 95% whereas oil furnaces with ratings over 80% are considered good. Older furnaces have about a 60% efficiency rating.
Although not calculated into the AFUE rating, furnaces equipped with variable speed fans are more efficient. Traditional furnace fans will turn on and blow the hot air at full speed and then shut off when the desired air temperature is reached. A variable speed fan runs for longer periods at a low speed and rarely goes to high speed unless you turn your thermostat up by many degrees. The variable speed fan will maintain an even delivery of heat and is very quiet. There is less consumption of electricity because the fan rarely runs at full speed.
How to Choose a Furnace
Outside of knowing your fuel source, you must determine if you are able to provide correct venting for a high efficiency furnace. You need a floor drain and PVC piping to the outdoors. If this is not feasible, choose a mid efficiency furnace.
There are different sized furnaces and oversized furnaces will cycle on and off more frequently. It is advisable to have a HVAC contractor do a load calculation of your home. This will take into consideration the size of your house, the insulation value of your walls, roof and windows plus other criteria.
Your climate has a bearing on choosing a furnace. If you live in a warmer climate, you may not need a high efficiency furnace because the return on your investment is not very high. A mid efficiency furnace will still save you energy dollars and it costs less.
You may want to install add-ons like a humidifier or an electronic air purifier which are over and above the basic furnace equipment. These will cost more and prices vary according to manufacturer.
Compare the features and consumer feedback on various brand names. Web sites such as Consumer Search have comprehensive reports.
Find a reputable dealer who will give you an in-home consultation to determine your needs and who will provide expert installation and service.
Even though you have to invest some money in buying a new furnace, the reduction of your fuel bills will certainly make up for it!
Sources Used:
- American Council for an Energy Efficient Economy
- Natural Resources Canada: Office of Energy Efficiency
- Home Tips
- Furnace Compare
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