DEAR SUN SPOTS: I hope you have the answer to this one. Two oil burner services say there should be no more than a 5-degree difference between the high and low thermostat settings; furniture and walls are reheated each time the temperature goes back up and the furnace runs for shorter periods.

An Efficiency Maine series on WMTW said money could be saved for each degree a thermostat is turned down regardless of range; the boiler runs more efficiently over a longer period even though it runs longer to reheat more than 5 degrees.

Is there a way you can determine which theory has proven correct? Perhaps one is old information, but which one? Thanks for any help. — No Name via email

ANSWER: As with the March 8 question on electric heat (http://tinyurl.com/7cptvqg), your individual situation and the wide variety of heating system options available mean Sun Spots cannot give you a precise answer. But she will offer up some facts for your consideration.

When Sun Spots showed your question to Mr. Sun Spots, he thought you were asking about something called “hysteresis.” (Sun Spots thought your question was about the manual adjustment of a thermostat, such as turning it down at night or when away, and she will address that as well.)

The dictionary.com definition of hysteresis is very technical (it partly reads “the lagging of an effect behind its cause”), so Sun Spots will skip that and go right to an explanation relating to home heating that she got from Wikipedia.

For a thermostat, hysteresis can be thought of as the range of temperature. Say you have your thermostat set at 70 degrees. For the furnace to maintain that exact temperature, it would constantly be clicking on and off, so it is set to cover a range. So it might be set to click on when the temperature drops to 67 degrees and go off when it hits 72 degrees.

That range is the thermostat’s hysteresis (“lag”) and can be adjusted by an expert. The wider the range, the less your furnace will go on and off, but the less comfortable you will be in your home.

(Mr. Sun Spots does not feel this explanation is thorough enough and launched into an explanation of “anticipation” and other factors, all of which are way too complicated for this column.)

As to whether you can save by turning your heat down more than the 5 degrees, Mr. Sun Spots agrees with Efficiency Maine and said: “You will always save by turning down your thermostat.” There are inefficiencies in starting and stopping a heating system. In one place the Sun Spots and her husband rented, a repairman provided the statistics on the amount of electricity the forced-air floor furnace used on startup, and it was astonishing.

However, there are limits to how much you SHOULD turn it down, as there are other factors to consider besides the thermostat setting, such as:

* Heat loss: How well insulated is your home? How quickly does the temperature drop? How much cold can you stand?

* What kind of heating system do you have, convective or radiative? Radiatives (for example, wood stoves) heat the objects while convectives (forced air furnaces) warm the air? (Startup inefficiencies may vary depending on the system.)

* Will a wide range of temperatures hurt objects in your home? (Sun Spots’ mother lives in a very old home with real plaster walls and was told that it would damage the plaster to let unused rooms get too cold.)

The question of whether to heat overnight or not bugged Mr. Sun Spots, who has his office in a separate building. In the depth of a Maine winter, letting the wood stove go out overnight meant the building was often quite cold (as low as 20 degrees) when he returned in the morning, but his experiments showed that feeding the wood stove for the night clearly used more wood.

At first he felt guilty about the extra wood, but then decided that the temperature extremes were too hard on his computers and other equipment. He now lets it drop into the 40s and 50s but tries not to let it get down near freezing.

You might want to contact Efficiency Maine and have them address your specific situation. You can find them at www.efficiencymaine.org, 151 Capitol St., Suite 1, Augusta, ME 04330-6262, 1-866-376-2463.

This column is for you, our readers. It is for your questions and comments. There are only two rules: You must write to the column and sign your name (we won’t use it if you ask us not to). Please include your phone number. Letters will not be returned or answered by mail, and telephone calls will not be accepted. Your letters will appear as quickly as space allows. Address them to Sun Spots, P.O. Box 4400, Lewiston, ME 04243-4400. Inquiries can also be e-mailed to sunspots@sunjournal.com.

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