Periodically the Federal government sets new standards for equipment minimum fuel efficiencies. As a result the furnace manufacturing industry is pushing the envelope on improving the efficiency of their equipment.
While oil furnaces often have a design service life exceeding 26 years, a unit that age has operational inefficiencies that would justify replacement with more efficient equipment.
Annual Fuel Utilization Efficiency
A furnace's efficiency is measured by annual fuel utilization efficiency (AFUE). AFUE is a measure of how efficient the appliance is in converting the energy in its fuel to heat over the course of a typical year. Specifically, AFUE is the ratio of annual heat output of the furnace or boiler compared to the total annual fossil fuel 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 flue and elsewhere.
- AFUE does not include the heat losses of the duct system, which may reach 35% of the energy for output of the furnace when ducts are located in unconditioned spaces.
Old, low efficiency furnaces with natural draft flue gas, continuous pilot light, thick walled heat exchangers may provide efficiencies ranging from 56% to 70%. New, high efficiency furnaces with condensing heat exchangers, fan-assisted exhaust and electronic pilot light may provide efficiencies ranging from 93% - 99%.
Generally the more efficient a furnace is, the more expensive up front (purchase price). Depending on the cost of fuel (oil), the initial cost difference for a highly efficient model can be recovered over the first few years of operation.
Choosing a high efficiency furnace
The Federal Trade Commission requires new furnaces to display their AFUE so consumers can compare heating efficiencies of various models.
Adams Manufacturinghas developed a condensing oil-fired furnace with an AFUE of 99; hard to improve on that.
By comparison, the minimum allowed AFUE rating for non-condensing, non-weatherized oil furnaces is 83 (weatherized is 81 and mobile home furnaces 75). So you can see there is a wide range of efficiency.
Williamsonis a well respected manufacturer of oil furnaces (in my neck of the woods). While not as efficient as the Adams line of condensing oil furnaces they are highly reliable and cost effective.
Also, consider this
Other important considerations during furnace replacement include:
- proper equipment sizing,
- modulating output,
- bio fuel compatibility and
- duct leakage.
The heating industry has long had a habit of over sizing HVAC systems. Over sizing causes high operational costs, comfort problems, and a higher rate of breakdowns (or early replacement requirements). The contractor you hire should perform heat-loss calculations on your home based on room x room inputs. Modulating outputs allow for equipment to run at lower burner and fan rates so you ramp up the operational size based on ambient temperatures.
These features cost more upfront but will reduce annual operating costs. With high fuel oil costs they should be given serious consideration.
For more information:
Read "Which oil furnace is the best to buy in 2012?" a Q&A answered by Elizabeth DiSalvo.
For more information on oil-fired furnace from a credible third-party source check out this Department of Energy article.