Retrofitting Your Furnace or Boiler
Furnaces and boilers can be retrofitted to increase their efficiency. These upgrades improve the safety and efficiency of otherwise sound, older systems. The costs of retrofits should be carefully weighed against the cost of a new boiler or furnace, especially if replacement is likely within a few years or if you wish to switch to a different system for other reasons, such as adding air conditioning (see the section on selecting and replacing heating and cooling systems). If you choose to replace your gas heating system, you'll have the opportunity to install equipment that incorporates the most energy-efficient heating technologies available.

Replacing Your Furnace or Boiler
Although older furnace and boiler systems had efficiencies in the range of 56%–70%, modern conventional heating systems can achieve efficiencies as high as 97%, converting nearly all the fuel to useful heat for your home. Energy efficiency upgrades 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. Newer systems may be more efficient but are still likely to be oversized, and can often be modified to lower their operating capacity.

Before buying a new furnace or boiler or modifying your existing unit, first make every effort to improve the energy efficiency of your home, then have a heating contractor size your furnace. Energy-efficiency improvements will save money on a new furnace, because you will need a smaller furnace. A properly sized furnace will also operate most efficiently. You'll also want to look for a dependable unit and compare the warranties of each furnace or boiler under consideration.

When shopping for high-efficiency furnaces and boilers, look for the ENERGY STAR® label. If you live in a cold climate, it usually makes sense to invest in the highest-efficiency system. 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.

You can estimate the annual savings from heating system replacements by using Table 1. The table assumes that both furnaces have the same heat output. However, most older systems are oversized, and will be particularly oversized if you significantly improve the energy efficiency of your home. Because of this additional benefit, your actual savings in upgrading to a new system could be much higher than indicated in the table.

Specify a sealed combustion furnace or boiler, which will 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. Furnaces and boilers that are not sealed-combustion units draw heated air into the unit for combustion and then send that air up the chimney, wasting the energy that was used to heat the air. Sealed-combustion units avoid that problem and also pose no risk of introducing dangerous combustion gases into your house. In furnaces that are not sealed-combustion units, backdrafting of combustion gases can be a big problem.

High-efficiency sealed-combustion units generally produce an acidic exhaust gas that is not suitable for old, unlined chimneys, so the exhaust gas should either be vented through a new duct or the chimney should be lined to accommodate the acidic gas.

Maintaining Furnaces and Boilers
The following maintenance should be provided by a heating system professional.All systems:
• Check the condition of your vent connection pipe and chimney. Parts of the venting system may have deteriorated over time. Chimney problems can be expensive to repair, and may help justify installing new heating equipment that won't use the existing chimney.
• Check the physical integrity of the heat exchanger. Leaky boiler heat exchangers leak water and are easy to spot. Furnace heat exchangers mix combustion gases with house air when they leak—an important safety reason to have them inspected.
• Adjust the controls on the boiler or furnace to provide optimum water and air temperature settings for both efficiency and comfort.
• If you're considering replacing or retrofitting your existing heating system, have the technician perform a combustion-efficiency test.

Forced-air Systems:
• Check the combustion chamber for cracks
• Test for carbon monoxide (CO) and remedy if found
• Adjust blower control and supply-air temperature
• Clean and oil the blower
• Remove dirt, soot, or corrosion from the furnace or boiler
• Check fuel input and flame characteristics, and adjust if necessary
•Seal connections between the furnace and main ducts.

Hot-water Systems:
• Test pressure-relief valve
• Test high-limit control
• Inspect pressure tank, which should be filled with air, to verify that it's not filled with water
• Clean the heat exchanger.

Steam Systems:
• Drain some water from the boiler to remove sediments. This improves the heat exchange efficiency
• Test low-water cutoff safety control and high-limit safety control
• Drain the float chamber to remove sediments. This prevents the low-water cutoff control from sediment clogs
• Analyze boiler water and add chemicals as needed to control deposits and corrosion
• Clean the heat exchanger

- Information Provided by EERE