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# Fuel savings versus thermostat setting

Member Posts: 708
I am coaching a family that is on assistance that has to pay for their oil for the first time. We know that the lower the thermostat, the lower the oil usage, but what is the actual relationship?

Is it a 4% savings for every degree reduction? For instance, assuming 1000 gallons a season at 70*, would 69* be (1000 x .96) and then 68* would be that number x .96 again and so on?

This is not for set-back, just steady temp.
Steve from Denver, CO

• Member Posts: 589
Do a Manual J

Change the interior temp on a somewhat accurate Manual J calc and you can show them.
• Member Posts: 708

What is a manual J calc?
Steve from Denver, CO
• Member Posts: 175
Savings

Most literature I've read, and I was reading some on Friday, says you save approx 3% for every degree you reduce it for a 24 hour period. If you reduce from 70 to 68, over the course of the heating season, you should save about 6%. With a nigttime setback, you'd save 3% if you setback the temp 3 degrees if the setback period is eight hours. Wallie's may disagree with this general information, but that is what the ordinary citizen is told by govt and energy conservation types.
• Member Posts: 29

Savings would have to be based on the differential between the indoor and outdoor temperatures.. If it is 68 degrees outside, and you setback from 69 to 68 degrees, your savings is 100 percent. It would change by according to the daily temperature ranges.
• Member Posts: 589
Manual J

That's a heatloss calculation that takes into consideration all of the insulation, infiltration, fenestration etc factors for a house and then tells you on a room by room and also overall basis, how much heat that room/house will lose at design day conditions. Design day is a particularly cold but repeatable wintert temperature. The manual J will be overstated since it includes a healthy oversize or recovery function but by changing the interior temperature at several typical outdoor winter temperatures you would be able to gauge the difference.

SlantFin has a nice heatloss calculation available on their web site.
• Member Posts: 9,546
Variable rate of savings

With outside temps.I have to agree with Foghorn.

If, and only IF this were a straight foreword drop in setting, and not a battle of set back.

3 or 4% for a 3000.00 heating season is not much, and thats a hefty bill for an average home say 2500 Sqft. Divided by the 5 months 1/2 of Oct thru the 1/2 of Mar of the season depending on your location. But if that kind of savings keeps a family on budget so be it.

Gordy

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