Furnaces

By Kenton Shepard

Using a programmable thermostat, heating and air-conditioning schedules can be adjusted according to a pre-set schedule. As a result, the equipment doesn't operate as much when it’s not needed. Programmable thermostats can store and repeat multiple daily settings (six or more temperature settings a day) which you can manually override without affecting the rest of the daily or weekly program.

Programmable thermostats contain no mercury, are more accurate and help reduce heating costs. They also allow circulation fans to be run without operating heating or cooling systems. Operating the heating/cooling system blower without activating the cooling system can make the home seem cooler and help reduce cooling costs.

Source: Kenton Shepard

A programmable thrermostat. The display has faded and should be mentioned n the report as needing maintenance.

Heating & Cooling System Locations

Heating and cooling systems should be located centrally in the home to shorten distribution runs. Shorter runs will have lower energy loss from leakage to surrounding materials.

FURNACES

Furnace Efficiency

Efficiency Comparisons: EnergyGuide Labels

EnergyGuide labels are labels which provide information used to compare the energy consumption of similar appliances.

The largest number on the guide states the estimated annual operating cost of the appliance. Some equipment, such as ovens or clothes dryers, may have two large numbers - one for electric, one for natural gas.

One of the most helpful features of the Energy Guide is a sliding scale that compares the appliance you're looking at to other models and brands. When you're comparing appliances, be sure to compare between models of similar size and capacity.

Source: Kenton Shepard

This label (shown in two parts for clarity) is for the high-efficiency furnace shown below...

Rating Heating System Efficiency

Furnace and boiler efficiency is rated by Annual Fuel Usage Efficiency (AFUE). The label showing the heating appliance’s rating should be on the exterior of the heating unit.

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% means that 90% of the energy in the fuel becomes heat for the home and the other 10% 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% of the energy for output of the furnace when ducts are routed through an unheated space.

Old, Low-Efficiency Furnaces

• Natural draft creating a flow of combustion gasses
• Continuous pilot light
• Heavy heat exchanger
• 68% - 72% AFUE

Mid-efficiency Furnaces

• Exhaust fan controls the flow of combustion air and combustion gasses more precisely (called induced draft)
• Electronic ignition (no pilot light)
• Compact size and lighter weight to reduce cycling losses
• Small diameter flue pipe
• 80% - 83% AFUE

High-efficiency Furnaces

• Condenses flue gasses in a second heat exchanger for extra efficiency.
• Cooler flue gasses can be vented with plastic vent.
• Sealed combustion
• 90% - 97% AFUE  

Source: Kenton Shepard

A high-efficiency furnace. Two large white PVC pipes are supply and exhaust air. The electrical shut off is located just below the upper pipe. The smaller pipes are condensate drains. the one on the left is an overflow. The fan induces draft, the actual air handler (blower) is in the compartment below. Mid-efficency furnaces will have a single metal vent.

Cooler exhaust

High-efficiency furnaces and boilers extract more heat from the combustion process than a lower-efficiency system by employing a secondary heat exchanger. This process not only provides extra heat for home heating, but also cools exhaust gases to a point at which plastic instead of metal can be used for exhaust vent material. When you see two  PVC pipes terminating at the exterior, chances are good the home has a high-efficiency heating system. High-efficiency vents are allowed to run almost horizontally.

Some high-efficiency furnaces and boilers use concentric plastic vent pipes in which one pipe is inside another. One pipe provides combustion air while the other exhausts the products of combustion.

Source: Kenton Shepard

A common configuration. The furnace supply vent is turned down to keep moisture out. The exhaust vent terminates at a “T” so that moisture is kept out, but natural air movement will help the vent draw adequately.

Condensation

One of the results of increased cooling of exhaust gases is that a larger amount of condensation is produced.  Condensation flows from the furnace to a container which houses a pump, which typically pumps the condensation to a laundry sink or floor drain or to the exterior. Condensation tube discharge locations vary among jurisdictions and it’s a good idea for inspectors to research local requirements.

Larger amounts of condensation increase the chance of moisture finding its way into the furnace cabinet and causing corrosion. Inspectors should look for evidence.

Source: Kenton Shepard

Left: corrosion stains in the cabinet.                           Right, A condensation hose has holes.

Source: Kenton Shepard

Three locations for air filters.

Electronic Air Filters

Electronic air filters have plates which must be cleaned occasionally. The frequency with which they'll need cleaning will depend on the filter manufacturer and indoor air quality. Inspectors hearing cracking or crackling sounds from the filter should write it up as needing maintenance. Filter plates can often be cleaned in the dishwasher.

Source: Kenton Shepard

An electronic air filter between the cold air return on the right and the furnace on the left. They won't all look like this one.