Heating Equipment

Energy Efficiency
Calculating the cost of your existing heating equipment compared to the savings possible with more efficient equipment is a little different than guides for heat loss. In fact, the heat loss from surfaces that need insulation, leakage, and windows is the basis for cost to run heating equipment. It has to supply the amount of heat being lost or else the indoor temperature will fall.

For starters, let’s notice the vertical line (on the graph below) that is identified as AFUE80 (Annual Fuel Utilization Efficiency represents the delivered heat divided by the heating value of gas provided to equipment. This line represents the minimum efficiency that a new furnace or boiler must have in the US. Until 2007 furnaces could be AFUE78. The change from 78% efficiency to 80%, a change of 2% above the base of 78%, represents a 2.5% decrease in heating cost for this change. Cycling, losses from the appliance enclosure, and other factors that waste heat are figured into AFUE to make it a realistic measure of in-home performance.

Check the right side of the graph, where we see AFUE98 equipment. This is quite high, though Energy Star complying furnaces, AFUE95, are available from all major manufacturers. If you had to replace a furnace and selected 95% rather than minimum allowable 80%, the 15% improvement, over a base of 80%, you could expect about 19% lower heating costs.

Energy Savings
What does this mean in dollars? You can probably get a good idea by taking the percentage improvement on your estimate of heating cost from utility bills. The guide shows heating cost for your type of house or apartment*, and tracing the energy cost line from the AFUE80 intersection left should provide a “ball park” estimate of your cost. Next, tracing the energy cost line from the AFUE95 unit, and observing cost to the left will be your estimate of cost using this equipment. Subtract from the cost of minimum efficiency equipment to figure savings.

AFUE80 is just the minimum code complying efficiency for combustion heating equipment (furnaces and boilers). Actually, steam boilers are allowed to be a little less efficient. To the left of the AFUE80 line lie efficiencies below the current standard. As we have “best” equipment at AFUE ratings 18 points higher than the minimum allowed, we also have older equipment 18 points lower – AFUE62. Some poorly performing equipment is probably worse than AFUE62, though we wanted to draw the cost border of the guide graph somewhere.

More on Energy Efficiency
How do you know the efficiency of your heater? The yellow DOE Energy Guide is present at time of purchase on an attached sticker or tag. Check if this guide remains stuck to the equipment cabinet. Most energy audit and heating service technicians will be able to test equipment combustion efficiency. This “steady state” efficiency is 10 to 15 points higher than AFUE for older equipment, though about 5 points higher than newer equipment. Installers may offer an opinion that the efficiency of present equipment is lower than actual, hoping to “make the case” for sale of a new item. See the table describing efficiency on the graph which identifies the likely AFUE of your equipment with age, type and features.

Be sure to ask your service firm whether equipment has efficiency defects that can be corrected. Note that a vent damper may raise the efficiency of older equipment by 10 points. When it is time to buy new equipment, proper sizing is important to for several reasons 1) new equipment that is too big may not achieve its rated efficiency, 2) comfort is often compromised by equipment that is too big, 3) equipment that is too big cycles off/on frequently and will not last as long, 4) an air conditioner that is too big may leave house air too humid. On average, heating equipment in the US is twice as big as needed.

*House types represented in the graphs are: apartment, bungalow, four-square, three flat.