If your furnace is old or needing major repairs, now is the time to think about a new one before the snow flies. 

In 1987 an act was passed stating that furnaces had to be 78% efficient, meaning that 78% of the heat had to go into the home.  Prior to that, some furnaces let 40% of the heat go outside through the vent. 

Today we have standard furnaces that are 80 percent efficient and some that are 90% or more and the 90% or more are considered high-efficiency.

What Do Furnace Energy Efficiency Ratings Mean?

All fur­naces that gen­er­ate heat with a flame pro­duce car­bon monox­ide.  Vent­ing this gas allows some heat to escape. Effi­cien­cy is defined as the annu­al heat out­put of the fur­nace divid­ed by the annu­al ener­gy it con­sumes. This ratio is called the Aver­age Fuel Uti­liza­tion Effi­cien­cy (AFUE).

Understanding Furnace Energy Efficiency Ratings

We will be talk­ing about gas fur­naces and boil­ers.  Ful­ly elec­tric fur­naces do not lose any heat through vent­ing gas, so they are all con­sid­ered high-efficiency.

A heat pump is not the same as an elec­tric fur­nace.  Heat pumps have exte­ri­or units and use a sep­a­rate mea­sure of effi­cien­cy. How­ev­er, most heat pumps have a back-up heat source, usu­al­ly a gas or elec­tric fur­nace, and that fur­nace will have an AFUE rating.

AFUE pri­mar­i­ly tracks heat lost through inten­tion­al vent­ing. It doesn’t fac­tor in heat loss due to gaps in the duct sys­tem or poor insu­la­tion. A fur­nace or boiler’s effi­cien­cy is only one part of the heat­ing equa­tion. If you have a hyper-effi­cient fur­nace but no insu­la­tion in the walls, your heat­ing bill will still be sky-high.

It’s impor­tant to under­stand that effi­cien­cy isn’t the only fac­tor that deter­mines oper­at­ing cost. A low-effi­cien­cy fur­nace equipped with a vari­able speed blow­er or two-stage heat­ing may con­sume less ener­gy over­all than a high-effi­cien­cy fur­nace run­ning at full power.

How to Determine If You Have a High-Efficiency Heating System

Man­u­fac­tur­ers are required to dis­play the AFUE on boil­ers and fur­naces. There will be a bright yel­low label on the out­side of the fur­nace. It should dis­play the AFUE and indi­cate whether it’s high effi­cien­cy or not. If the label is miss­ing or dam­aged, you can look up the mod­el num­ber online to learn the AFUE. You can also sim­ply look at the lay­out of the fur­nace to deter­mine if it’s high effi­cien­cy. Here’s how:

If the fur­nace vents to the chim­ney or roof via a met­al flue, then it’s stan­dard effi­cien­cy. If the fur­nace has a pair of PVC pipes act­ing as draw and vent, that’s a sign of sealed com­bus­tion, mean­ing that it’s high-efficiency.

How Does Ener­gy Effi­cien­cy Impact Cost?

High effi­cien­cy fur­naces cost more but they save on ener­gy con­sump­tion. The ques­tion is, are the sav­ings enough to jus­ti­fy the high­er ini­tial pur­chase cost? The answer depends on how your home is designed and insu­lat­ed, how much you use your fur­nace, and how long you plan to be in your home.

The final cost of a fur­nace install will depend on the size and lay­out of your home, as well as the make, mod­el and fea­tures of the fur­nace. In gen­er­al, most man­u­fac­tur­ers price their high-effi­cien­cy fur­naces at one-and-a-half to two times the cost of a stan­dard-effi­cien­cy mod­el. That could be any­where from $2,000 to $6,000.

In addi­tion, installing a home’s first high-effi­cien­cy fur­nace or boil­er will mean extra cost, since the sealed-com­bus­tion sys­tem will require new vent­ing (the dual PVC pipe sys­tem). Depend­ing on your home’s lay­out, this may be a minor expense or a major headache. It may also require you to rework the ven­ti­la­tion for a gas water heater. Every home is dif­fer­ent, but It’s rea­son­able to fig­ure in a few hun­dred dol­lars here.

There may also be tax impli­ca­tions that affect your cost. These change based when reg­u­la­tions are passed, extend­ed or repealed. So check the lat­est infor­ma­tion from an offi­cial source, such as the DOE’s Ener­gy Star site.

Deter­min­ing a furnace’s effi­cien­cy is an impor­tant first step, but it’s only part of eval­u­at­ing your home’s over­all ener­gy consumption.