which uses more oil for heating?

[frugalmum]

We have been trying to figure out which would use more oil-- we live in a very large house (about 3700 sq ft). 

1) Keep thermostat on 50F during the day (7AM-10PM) raising it to 65F at night (10PM-7AM).

or

2) Keep thermostat at 65F 24 hours and let it maintain that temperature.

In other words, will it use as much oil to jump from 50F to 65F in night as it would to maintain the temp during the day?

The house heats unevenly and typically is about 4-5 degrees colder than the thermostat.  We can supplement during the day with space heaters in common areas but won't leave them running at night for safety reasons.  65 is the coldest we can go at night (which realistically is about 60) because of 2 children with severe asthma.

tia!

[mich]

I am always skeptical of information that says it's cheaper to maintain the temp that to heat up a house. We set our heat at 62-65 during the day and drop it to 50 around 8pm. it stays there until around 10am the next day. It takes about an hour to heat the house up in the morning. But for the 14 hours it is down it does not run once. It would be very hard to convince me it would be cheaper to have it running on and off all night. But I hate sleeping in a warm room, so even if it was cheaper I don't think I would do it.

I understand your settings are opposite. You could try both methods for a month and compare. You are trying to see if using your primary heat is cheaper than the secondary heat + heat up (at night) costs?

[yeahwhat]

Unless you have a geothermal system (and then depending on how your system works), you save money turning the temperature down for several hours at a time, day or night.  The other possible exception would be using electric heat sources if you were on time of day billing. 

[frugalmum]

Yes exactly, I'm trying to figure out if the primary heat maintained at a steady temp is cheaper than the lower setting + back up + heat up.  It does take about an hour to get the 10-15 degree jump where as maintaining at 65 with it being 50 out (and it will get much colder soon) the heat is running every 3-4 hours for 15-20 minutes.

I am very nervous about running the space heaters so much, but electricity is a fraction the cost of what oil is, plus we can heat the house selectively, 4-5 rooms instead of all 17 rooms.

[SleeplessMommy]

First a quick answer to your stated question. If your choices are "constant temperature for the house at 65 degrees" versus "setback thermostat to 60 degrees at night, 65 during daytime", and both heat sources are the same with no smart metering on electricity, then the setback thermostat will always be more cost effective. The short "reason" is that the higher the temperature inside, the more heat energy is lost to the outside.  Lower temperature inside at night = less heat lost = less oil needed to replace it.

You have a more complicated situation, though. You have a choice of electric heat (part of the house) vs. oil heat (all of the house). And you don't want the pipes to freeze.  There are 3 things to consider: efficiency of your heating systems,  insulation of the house, and government programs.

heating system efficiency: if you have an older oil fired furnace or boiler, it may have a combustion efficiency of 50-80%. (plus addition energy losses in the ductwork) When you get the system serviced (every year) you can ask them to tell you the combustion efficiency. The sensor they use to test the system will be able to give a printout. If you are at 50-60%, system replacement can have a good payback. If you have forced air ducts, inspect them where visible to make sure they are all connected. Disconnected ducts are pretty common and can cause uneven heating.

With the electric heaters, you can find out exactly what each heater is costing with a kill-a-watt meter (about $25 at Amazon). If you want to use electric heat on the sleeping areas in the long term, consider a "ductless mini split" heat pump. They are very efficient. http://www.energysavers.gov/your_home/space_heating_cooling/index.cfm/mytopic=12630

Insulation. this website explains lots:

http://oee.nrcan.gc.ca/residential/personal/new-home-improvement/choosing/insulation-sealing/materials/khi-intro.cfm?attr=4

Even if you are a renter, a little weatherstripping can go a long way, at a cost of a few dollars per window. Same with insulating blinds, made from supplies at the JoAnne fabrics.

Government/utillity programs:

If you are low income, apply for liheap and weatherization (even if you are renting). Weatherization is spending thousands per home, and in some cases will replace the furnace, broken windows, or an ancient fridge. Call your electric utility and ask about free or reduced price energy audits. There are many programs and tax incentives depending on where you live. They are all listed here:

http://www.dsireusa.org/