I know that every one of you have been questioned about efficiency by your customers, and you do your best to give your description or cite examples on the topic. In many sales presentations your customers will often mention that they want a unit that has the best AFUE rating. They may even mention how they have spent time on their computer trying to find a heating appliance that will give them the highest rating, which in turn will give them the best value for their fuel expense. Of course, as we all know, these ratings will depend on the fuel used and the type of system selected. Examples of fuel values are natural gas = 100,000 Btu’s per therm; LP gas = 91,000 per Btu per gallon; and #2 fuel = 138,000 Btu’s per gallon.
When it comes to selecting the type of unit that will have the highest efficiency rating we often find that the gas units have ratings in the 90% range, while oil units will be at 87% mostly due to the new Department of Energy requirements.
True efficiency often varies due to such factors as stand-by loss, system sizing, duct air leaks, stack loss or jacket loss. But the real issue regarding efficiency goes well beyond the above, because they are related only to the boiler, furnace or water heater. What is considered by an energy auditor is the entire house and that is often referred to as the house envelope. The real energy auditors are not reading the existing equipment label for sizing, which will more often lead to the oversizing of the new replacement equipment.
In preparing for a whole house audit, the consumers is advised how a complete audit is performed, such as the factors that are addressed in Manual J and how the results can help the customer get the most value for their fuel dollars, regardless of the fuel selected.
When I talk efficiency, I think total, which means devices that draw a too much electrical current such as the three-piece circulators, non-set back T Stats, boilers that are always functioning at higher than required water temperature, tank-less coils or the lack of combustion air.
Air leaks around door and windows and how warm the basement is when doing your audit (and where that heat should be going) should also be taken into consideration. I would prefer this 70 degree energy to be going to the living space rather that the basement, and this is should be shared with the home owner. Then there are the newer indoor/ outdoor temperature resetting devices that will balance the boiler water temperature based on either the outside temperatures or the heating cycles of each zone. And they have proven consumer energy savings of 20%.
Another very good energy auditing tool is an electronic thermometer; this device can measure the amount of heat that could be leaking from the outside walls or ceilings due to something as simple as the lack of (or even no) insulation. In closing, let me remind everyone that regardless of what fuel is used, in order for a new piece of high efficiency equipment to maintain its efficiency an annual tune up and accurate combustion test is a must.
Also a reminder, when it comes combustion efficiency testing equipment, make sure that it is calibrated on an annual bases.