DISCLAIMER: I have to say this upfront because I only have estimated data so far.  I'll try to fill in a clearer picture as time goes on and I have more to go on.

House: 2100 sq ft of conditioned space, 1.5 story, 2 zones. 
Previous System: central a/c, oil-hot water baseboards, cost per month $300 for oil, which included winter heating and all domestic hot water.  Don't know a/c cost to run.
Current System: 4 ton GeoMax 2 (3 heat/2 cool) closed vertical loop with VisionPro 8000 thermostats, setbacks enabled, Adaptive Recovery on, weekdays:60; mornings and evenings: 68. weekends day: 68; all nights 60.  Same settings in both zones.  Desuperheater with AirTap also on 40 gal water heater for domestic.

System was installed during October 2009, during which we had no heat and no a/c, just hot water from the oil burner until the very last minute.  I'm basing the current post on electric usage of $105 for the month, and assuming this is the monthly cost without heating or cooling.  The $105 covers our computers, lighting, appliances, etc.

October          : $105  (pre-geothermal)    KWh: 677      KWh/day: 23.3
November      : $130  (with geothermal)   KWh: 1097    Kwh/day: 35
Not sure how useful, but according to degreedays.net, we had 380 heating degree days during the month of November.
Savings: $300 oil - $25 increased electric = $275 in November.
Cost of Geothermal System (less upcoming rebate!) = $17,000. 
Payback Estimation: 61 months (5.1 years)

I'm sure much of this data will change as I gather more data...cost of oil, cost of electricity, etc.

That's a pretty big energy usage spike, no oil used in October, and $300 worth of oil used in November.  You sure your numbers aren't off?

 

Hey TG....better go read that again after you have some coffee. 

My point is it's doubtful he would have used $300 worth of oil in November if he still was heating with oil.  If he didn't need the heating system in October at all.  The Winter gets colder gradually, it's not 70 degrees in October and -20 in November.... unless your on the moon where it 200 degrees in the sun and -180 in the shade.

 

I see your point.

The $300 oil "estimate" was based on previous billing given to me by the previous owners. Basically, it was an "budget" payment plan, where the total cost of oil for the year is spread out over 12 months, so the oil bill for the year was $3600, divided by 12 for $300 per month. Yes, it would have been much lower in the spring summer and fall, and much higher in winter, but averaged out is $300/month. That's what I would be paying per month for all heat, averaged over the year. I'm using that as my baseline because I knew it was a cost I'd have to deal with if I moved into the house, so I'm translating that into savings per month by not having oil. My parents' house, very similar size, style, oil heat/baseboards, also costs $300/month on the budget plan, so I'm assuming the savings estimate is good.

And no, I no longer have oil bills. They stopped in October, and I gave away all the old oil left over in the tank. I made someone very happy that day.

My energy spike was $30 for November heating.

Ok, I see now.  Unfortuantely it's really difficult to see what the saving are based on someone elses energy usage.  They might have been the type that couldn't stand to be the slightest bit cold, so they would have the thermostat set at 75 degrees + all winter instead of just putting on a sweater.

Also remember to check for leaks / installation problems.  Installation saves far more energy then any type of heating method.  As for budget plans, I'm not a fan.  More often than not they over estimate your energy usage and have you paying a higher than normal amount on there budget plan.  Personally I rather know what I'm using every month and if there is an energy usage cost spike I can take steps to resolve the issue. (Weather it's turn the thermostats lower, adjust setbacks, checking for drafts / air leaks.)
 

True, but I'm assuming because I know my parents house is similar in size/construction/insulation, and that they use $300/mo oil, and that their house is *never* 75 :-) I wish it had been..growing up was cold...that $300 is a good ballpark.

I remember touring the house I'm in several times prior to buying it while the owners still lived in it, during the Winter of 08-09, and it was warm, and comfortable, but not overly warm, probably 70 based on temps now and comfort level. I did patch a six inch hole between an upstairs closet with louvered doors and the outside soffit! I'm sure that helped a bit.

I agree with not having budget billing if at all possible. Some people need the predictability (my mom does) and the oil company refunds/credits the difference if there is any. I was offered budget billing for my electricity but I declined for that very reason you stated. It becomes difficult to estimate any usage/cost/savings at a glance if it's the same price all the time.

We were able to get some historical usage figures for our house from our electric and propane company when we moved in since the information was not of a sensitive nature. Just mentioning this in case you want to try to contact the oil company to try and find out the number of gallons filled on certain dates and the cost. The electric company gave us the information verbally, and the propane company gave us a printout.

You might want to get old electric bills from previous owners....oil furnaces use electricity as well. You also likely have savings on ac and hot water that will improve payback.
Joe

I actually have electric bills (at least, the costs) going back a year for the previous owners, as well as oil gallons and prices. I didn't know how much to factor them in, since we're a whole new family with different electrical uses. I figured $105/month for us, but I'll look back at what they spend spring and fall, also.

In my humble opinion, the cost of the oil is not as meaningful as gallons used. Is it possible for you to get actual gallons of oil used for previous years? I can tell you, the price of oil was never the same for me from year to year. I used a very simple method for my "crunching of numbers."

I had 4 years worth of oil use data (but if you have one year, just use that one year). For my specific case, I found the heating degree days for each year and the gallons of oil used each year. I divided gallons of oil by HDD so I came up with an average rate of ~0.15 gallons/HDD.

So, to calculate my savings over the heating season, let's say the 2008/2009 heating season, I find out how many heating degree days there were, I multiply that number by 0.15 and find out approx how many gallons of oil I would have used. I then find out how much oil cost for that heating season and estimate what I would have paid in oil.

I then compare that to the KWhrs used and multiply by the cost of electricity and that tells me what I paid extra in electricity. Since the cost per KWh increases annually for me I could not just compare last years cost with this years.

Just some food for thought...

For deducing the overall electric bill I highly recommend Compact Fluorescent lighting.  I replaced pretty much every light bulb I could in the house, with the exception of the bathroom vanity.  Just keep careful track of when you buy them, I initally had a 10% failure rate with them, I was planning on returning them for replacements, but my wife was cleaning the house and thrown them away one day.  I've been keeping careful track of my electric usage every month, and I deem it my personal challenge to use less KWH each month then the same month last year.

Ok, here's some more data. The previous owners (an elderly couple) spend $932 for electricity last year (2008), or about $77/month. I'm not sure how relevant this is for us. We have a mix of CFL and low wattage incandescent bulbs. We do have a couple computers that are on all the time. Not sure what they had. Their peak electricity bill was for July and was $127. I'm assuming this included a/c. March/April/May, and September/October were all about $70, so perhaps it's safe to call that their base rate, and assume that their a/c "increase" was $57 for July.

For oil, they used 900 gallons of heating oil in 2008, and cost an average of $3.43 per gallon, for a total cost of $3087.

There was a total of 5336 heating degree days in 2008, which after dividing the fuel (900) by HDD (5336) gives me 0.169. So basically, 0.169 gallons of oil needed per heating degree day.

I should be able to then multiply the "coefficient" of 0.169 by the HDD of any month to find the amount of oil I would have used, then find the price of oil for the month, multiply, and compare to electrical increase over my base assumption of $105/mo.

Let's try it for November:
380 HDD * 0.169 = 64 gallons of oil (saved) * current price ($2.80) = $180.
Electrical cost for geothermal heat in November was $25, so a savings of 180-25=$155.

Was that right???

Don't confuse me with facts.

Your logic is irrefutable.

My only concern is mixing thermostat setbacks with geo.  Unless you are careful, that electric heating element is going to come on.  I personally feel that using the electric resistance defeats the purpose of going with geo in the first place.  My electric resistance coils are on their own circuit.  They can't come on unless I want them to.  I've been in my house for a year now and have NEVER turned them on.  A neighbor of mine learned this lesson the hard way.  It's better to take steps now than to find out when you get an out of whack electric bill.

Good luck,
Ed
Check out my house at:  www.GouinGreen.com   

Once again, running a 4 COP heat pump 4 times as long as a 1 COP aux coil
costs the same. Blanket statements where auxilliary coils are concerned really aggravate me as it has a lot ot do with system design.
If 2 stages are good, why won't folks accept that 3 are better?
joe

Somehow we need to communicate that oversizing geo is bad, and that north of I-10 a little bit of aux is OK, even desireable, and that north of I-40 a moderate amount of aux is part of the program, no ifs ands or buts.

I generally agree with both of you guys, but I 've got to say something here. Let me start by saying that undersizing the heat pump and designing with Aux heat is certainly an accepted practice and gives you the best bang for the buck in many if not most cases. But Joe, obviously running the COP 4 heat pump 4 times as long as the aux coil uses the same amount of electricity, but you get 4 times the heat! If you do use the same amount of power you'll either be very hot running the heat pump or very cold running the Aux! I'm sure this isn't what you were trying to say, but that's how it sounded.

Engineer - I think you're making a "blanket statement" here - There are plenty of cases north of I-40 (or even I-90) where it makes sense to size to the full design load. Again, I'm not disagreeing that most designs can benefit from aux heat as a way to reduce up front costs, but it really comes down to the individual situation and the preferences of the designer and homeowner.

I don't mean to pick a fight - I realize that it can be frustrating when trying to explain that using some resistance heat is perfectly acceptable - just don't swing too far the other way - there are a lot of reputable designers and contractors that design to 100% of load in cold climates for certain situations. And while you should certainly use caution in terms of "over-stressing" the ground loop, if a system can handle a load without using resistance heat, then it should.

How can I tell if the system is oversized? We had 32 F weather all last night and the system was cycling on and off maintaining at 70 quite easily. And the aux strips are OFF on the breakers still. All my setbacks are with aux off at the moment, just for testing/learning. Setbacks on an intelligent thermo should never cause aux to go on.

When it comes down to it...
1. am I comfortable? Yes!
2. is this costing a lot less money that if I had oil? Yes!
3. does it really matter (to me) whether my heating electric bill is $25 or $30 because strips came on a couple times during the month? Nope.

The aux is off permanently now just so I can see how the system performs. It's having absolutely no trouble maintaining 70 while it's 32 outside, and in fact, is probably spending just as much time off and on.