How to Improve Oil Furnace Heating Efficiency

Several Factors Could be Causing You to Pay More for Home Heating Costs than You Should

By Mark J. Donovan

Recently I had an HVAC expert come to my new home to assess what to do about my oil fired furnace. Though the home has approximately ten percent more square footage than our previous home, our annual home heating costs are nearly 75% higher. I was at a loss for what could be causing the lower oil furnace heating efficiency and asked the HVAC expert to come out to see about putting in a new and more efficient oil fired furnace.

The first thing the HVAC expert was able to tell me as soon as he saw the oil boiler was that it was old and inefficient. He explained that my oil boiler was a Peerless boiler that was manufactured in the 1980’s and was not that efficient compared to the new ones today.

He stuck a probe into the duct exhaust and confirmed that the oil burner was only operating at 82.5%. That level was considered good for this particular vintage of an oil fired furnace, but not good in comparison to today’s oil burners. Today’s oil burners in comparison operate at 87% to 91% efficiency.

The other thing he pointed out about my oil burner was that it was “oversized” for the home. More specifically it operated at a 1.5 gallons/hour fuel consumption rate, if it were to operate non-stop for an hour. For my home, he suggested that I should be using an oil burner with a fuel consumption rate of 0.9 gallons/hour. He indicated that not only would I save on home heating costs due to the lower fuel consumption rate, but that my house would also have steadier and more consistent home heating. Using a lower burn rate oil burner causes the furnace to run longer and thus provide more continuous heating. On the surface that may sound like a bad idea from a cost of operation standpoint.

However, he explained to me that by having the furnace run for longer periods and then subsequently shut down for longer periods, would overall result in a lower amount of oil consumed in an hour.

He also pointed out that the exhaust temperature from my oil burner was approximately 475o Fahrenheit, or approximately 175o hotter than it should be. That extra heat is all wasted energy going up the chimney. The extra heat was caused by the oversized burner and its associated 1.5 gallons/hour fuel consumption rate. With a lower gallons/hour consumption rate the exhaust temperature would only be around 300o.

Another concern he saw with my boiler was that the burner itself was sucking air directly in from our basement.

Note that a burner needs both fuel and oxygen to cause combustion, thus the air intake on the oil burner. He said that by pulling air into the burner from outside the home, rather than from the basement, we’d also improve the heating efficiency of our furnace and lower our home heating costs. He explained that by having the oil furnace draw air directly in from the basement that a low air pressure was being created in our basement. In turn, that low pressure in the basement was causing warm air in the home itself to be sucked into the basement, to in effect, feed the oil burner.

How to improve oil-fired furnace efficiency.

And subsequently, by creating a lower pressure in the main living area of our house, cold outside air was being drawn into our home through door and window cracks. Thus the main living area of our home was effectively being cooled off by sucking cold air into it while the furnace attempted to heat it.

And another important fact, even when the oil furnace was not running, the residual high chimney temperatures produced by the oil burner when it was on, was causing warm air from the basement to continue to be pulled up the chimney. Thus, even when our furnace was not operating its effects were causing heat to be pulled from the home.

The HVAC expert explained that ductwork, and a smaller motorized fan assembly, should be installed on the oil burner itself. The other end of the ductwork would be fed out the side of the home. This way outside air would be the source of oxygen for the oil burner.

Lastly, the HVAC expert asked to go up into our attic. This is where one of the two hot water to air heat exchangers reside, along with all the duct work to pump air into all the second floor bedrooms. As soon as the HVAC expert walked up into the attic he pointed out a significant problem. He pointed to the R-value numbers on the rigid ductwork associated with the main trunk of the heat exchanger. The R-value was only a 4.3. Similarly, the various lengths of flexible ductwork tubes that flowed to the second floor bedrooms only had an R-4.2 value. He explained that the attic, with its frigid winter temperatures, was sucking out much of the oil furnace’s generated heat along the lengths of the poorly insulated ductwork. He recommended that we spray foam insulation around all of the ductwork so that we improved the insulation R-value to at least an R-12, and preferably higher.

So based upon the recommendations of the HVAC expert we are installing a new and modern oil fired furnace that will operate at greater than 87% efficiency and that has a fuel oil consumption rate of only 0.9 gallons per hour. In addition, ductwork will be installed to draw air from outside the home to feed the oil burner. Lastly, in the very near future I am having all of the attic HVAC ductwork insulated. Hopefully, with these three major changes we’ll improve the heating efficiency of our home and dramatically lower our annual home heating costs.

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