Heating - Replacing Your Furnace Or Boiler Although older forced-air and hot water boiler systems had efficiencies in the range of 56% to 70%, modern heating systems can achieve efficiencies as high as 97%, converting nearly all the fuel to useful heat for the home. Conservation efforts and a new high-efficiency heating system can often cut your fuel bills and your furnace's pollution output in half. Upgrading your furnace or boiler from 56% to 90% efficiency in an average cold-climate house will save 1.5 tons of carbon dioxide emissions each year if you heat with gas, or 2.5 tons if you heat with oil.
If your furnace or boiler is old, worn out, inefficient, or significantly oversized, the simplest solution is to replace it with a modern high-efficiency model. Old coal burners that were switched over to oil or gas are prime candidates for replacement, as well as gas furnaces with pilot lights rather than electronic ignitions.
Before buying your new furnace or boiler, first make every effort to improve the energy efficiency of your home, then have a heating contractor run a heat-loss calculation to size your new furnace. Energy-efficiency improvements will save money on the furnace, because your home will need a smaller furnace. A properly sized furnace will also operate most efficiently.
If you live in a cold climate, it usually makes sense to invest in the highest-efficiency system available. In milder climates with lower annual heating costs, the extra investment required to go from 80% to 90%-95% efficiency may be hard to justify. When shopping for high-efficiency furnaces and boilers, look for dependability, and look for the ENERGY STAR(r) label. Buy a system with a good warranty and a reputable company to back it up.
When buying gas and oil systems, specify sealed combustion. Sealed-combustion furnaces bring outside air directly into the burner and exhaust flue gases (combustion products) directly to the outside, without the need for a draft hood or damper. They generally burn more efficiently and pose no risk of introducing dangerous combustion gases into your house. In furnaces that are not sealed-combustion units, back-drafting of combustion gases can be a big problem. How To Buy An Energy Efficient Gas Furnace | Figure 18: Efficiency Recommendation | | Product Type | Recommended AFUE (a,b) | Best Available AFUE | | Residential Gas Furnace (c) | 90% or more | 97% |
(a) AFUE (annual fuel utilization efficiency) is a measure of heating efficiency on an annual basis. The DOE test procedure defines AFUE as the heat transferred to the conditioned space divided by the fuel energy supplied.
(b) Based on DOE test procedure, see 10 CFR, Sub-Part B, Appendix N.
(c) Residential gas furnaces include those fired by natural or propane gas, with input ratings less than 225,000 Btu/hour. | Cost-Effectiveness Example | | Performance | Base Model (a) | Recommended Level | Best Available | | AFUE | 78% | 90% | 97% | | Annual Energy Use | 790 therms | 685 therms | 635 therms | | Annual Energy Cost | $320 | $270 | $250 | | Lifetime Energy Cost (b) | $4,600 | $4,000 | $3,700 | | Lifetime Energy Cost Savings | ----- | $600 | $900 |
(a) The efficiency (AFUE) of the base model is just sufficient to meet current U.S. DOE national appliance standards.
(b) Lifetime energy cost is the sum of the discounted value of annual energy costs based on average usage and an assumed furnace life of 20 years. Future gas price trends and a discount rate of 3.4% are based on Federal guidelines (effective from April 2000 to March 2001).
Cost-Effectiveness Assumptions: Annual energy use calculation is based on the standard DOE test procedure. Furnace model: heating capacity of 70,000 Btu/hr. Usage assumption: 2,080 heating load hours per year. Assumed gas price: $0.40/therm, the Federal average gas price in the U.S. How to Select an Energy efficient Residential Furnace: For furnaces purchased through commercial sources (retailer or distributor), look for the EPA/DOE ENERGY STAR (r) label; all ENERGY STAR (r) models meet this efficiency recommendation. Visit the an ENERGY STAR (r) Web site for a list of complying models. Alternatively, look at the yellow "EnergyGuide" label to identify models with an AFUE that meets the Recommendation.
For a contractor-supplied gas furnace, specify an ENERGY STAR (r) qualified model, or one with an SEER that meets the recommended level.
Condensing Furnaces: All models that meet the recommended levels are "condensing" furnaces. This technology takes advantage of normally exhausted heat in the furnace's flue gas. Condensing furnaces require slight modifications in installation and usually are considerably more expensive than standard efficiency models; consult the cost-effectiveness information to help determine the range of price premium that is justified for your location and fuel price.
Sizing: Over sizing of furnaces, besides raising purchase cost, will result in weaker energy efficiency due to excessive on-off cycling. The required furnace capacity should be determined based on the referenced ACCA calculation procedure (see For More Information).
Duct Sealing: Average U.S. homes lose more than a quarter of their heating energy through leaky ductwork. Poor sealing of ducts can also generate comfort problems and, in some cases, cause back drafting of gas-fired equipment (furnaces and water heaters). Ductwork should be inspected and sealed in conjunction with furnace installation.
User Tips: Consider leaving your furnace off during unoccupied hours or using a set-back thermostat to minimize unnecessary operation of the unit. |
