Energy Tip:
Install a programmable thermostat to keep your house comfortably warm in the winter and comfortably cool in the summer.
Furnace Efficiency
Annual Fuel Utilization Efficiency
The Federal Trade Commission requires new furnaces or boilers to display their Annual Fuel Utilization Efficiency (AFUE) so consumers can compare heating efficiencies of various models.
AFUE is the ratio of heat output of the furnace or boiler compared to the total energy consumed by a furnace or boiler. An AFUE of 90 percent means that 90 percent of the energy in the fuel becomes heat for the home and the other 10 percent escapes up the chimney and elsewhere. AFUE doesn't include the heat losses of the duct system or piping, which can be as much as 35 percent of the energy for output of the furnace when ducts are located in the attic.
Existing, older furnaces fall between 68 and 72 percent AFUE. Existing, older boilers test a little higher at 72 to 76 percent AFUE. Since 1992, furnaces are required to have greater than 78 percent AFUE, and boilers must have greater than 80 percent AFUE.
Estimating fuel-cost savings and payback
If you know the AFUEs of the systems you want to compare, you can estimate the annual savings from heating system replacements by using Table 1 below. For instance, if you have a conventional, older system with a pilot light and no vent damper installed, it will probably have an AFUE of about 60 percent.
|
Annual Estimated Savings for Every $100 of Fuel Costs by Increasing Your Heating Equipment Efficiency* |
|||||||||
|
Existing System AFUE |
New/Upgraded System AFUE |
||||||||
|
55% |
60% |
65% |
70% |
75% |
80% |
85% |
90% |
95% |
|
|
50% |
$9.09 |
$16.76 |
$23.07 |
$28.57 |
$33.33 |
$37.50 |
$41.24 |
$44.24 |
$47.36 |
|
55% |
---- |
$8.33 |
$15.38 |
$21.42 |
$26.66 |
$31.20 |
$35.29 |
$38.88 |
$42.10 |
|
60% |
---- |
---- |
$7.69 |
$14.28 |
$20.00 |
$25.00 |
$29.41 |
$33.33 |
$37.80 |
|
65% |
---- |
---- |
---- |
$7.14 |
$13.33 |
$18.75 |
$23.52 |
$27.77 |
$31.57 |
|
70% |
---- |
---- |
---- |
---- |
$6.66 |
$12.50 |
$17.64 |
$22.22 |
$26.32 |
|
75% |
---- |
---- |
---- |
---- |
---- |
$6.50 |
$11.76 |
$16.66 |
$21.10 |
|
80% |
---- |
---- |
---- |
---- |
---- |
---- |
$5.88 |
$11.11 |
$15.80 |
|
85% |
---- |
---- |
---- |
---- |
---- |
---- |
---- |
$5.55 |
$10.50 |
|
90% |
---- |
---- |
---- |
---- |
---- |
---- |
---- |
---- |
$5.30 |
*Assuming the same heat output
To estimate the amount you're spending on gas for heating, you can take your gas bills from the last three years, add them up, and then divide by three to get an average yearly cost. If you use gas for purposes other than space heating, like cooking or water heating, you have to account for this by subtracting the cost of the gas billed for these uses as follows:
1. Add up your gas bills for the four warmest months when heating is not needed.
2. Multiply the result by three to get an estimate of annual nonheating gas costs.
3. Subtract the result from your average yearly cost to get the space-heating cost.
If you want to estimate the annual return on investment and the number of years required to repay your investment, you can use the following simplified formulas:
- Annual savings / initial investment = Annual return
Example: $250 / $1500 = 0.17 or 17% annual return on investment
- Initial investment / annual savings = Years to Pay Back
Example: $1500 / $250 = 6 years
In many cases a 10 year payback or better is considered cost-effective.