I own a vacation property in northern Minnesota. Over the past 2 years, I have renovated it, almost completely... including a re-wiring of the kitchen and the bathroom. I installed electric heaters (a combination of base-board and wall heaters). Everything worked fine through October 2016, at which time I winterized the place... and it has largely sat unheated and unused since then.

Our electric bills at this place, when it is in use (May-October) are typically anywhere from $30 per month to as much as $70 per month. The high bills are when it's hot and we run the air conditioner. In the winter, the electric bill is typically about $20 per month. About half of that bill are various fees that are straight fees. I run an exhaust fan in the basement all winter because the basement is humid. This fan pulls (according to its specifications) 0.75 amps, which equates to about 65 kW-hours per month.

Last month, my electric bill was $100. We "used" 842 kW-hours of energy. I immediately assumed that I had left something on, whether it was a heater, the stove, or something. When I visited yesterday, there was no evidence of anyone entering the premises and no item (other than the exhaust fan) was running or on.

Does anyone have any ideas as to what could be causing the large electric bill?

Ideas that I have had/heard:
1. A mistake by the power company. I spoke to the power company and they confirmed that the bill is correct. They reported huge differences in power usage on a day by day basis. They have promised to mail me this information (but they couldn't email it, apparently).
2. Someone is stealing electricity from me using one of the exterior outlets. I didn't see any evidence of this (it's Minnesota... there were no tracks in the snow).
3. A co-worker mentioned that something could have a short, which could draw a lot of power. I don't have an explanation for that.

The one curious thing... is that I looked at the electric sub-panel in the detached garage. It contained a 30-amp, double-pole breaker that I don't recall being there before. I can't think of a single item in the garage that would require 240 volts of electricity either.

If someone is stealing electricity then that would be the obvious choice as to why the bill is higher. But also you didn't mention if you have a water heater that is electric? Sometimes they can cause unusual electric consumption. If you don't remember there being a breaker then turn it off and put tape over it.

Pull the cover off the panel and see where the 240 circuit goes. Garage heater? Should be a 240 outlet somewhere. Do you know what a standard 240 looks like?

Might help this mystery if you tell us
did you hire an electrician during renos
does someone plow in winter
do you leave your garage unlocked

I would purchase an Amprobe type Current Meter. Clamp around a wire, and it will tell how much of a load in amps it is drawing. If you can safely clamp around Drip Loop if Ariel, with Panels Off and you see a load, someone may have Tapped onto your Power. See how much the unknown 30 Amp Breaker is Drawing. Take Note, Turn off and leave off. If your Dryer, AC, or something stops working, turn it back on, you now know what that is. The current meter will measure the Total Load, or Individual Loads, of where you place the Amprobe. You can Measure the Load of Line 1, Line 2(main Hots), and the Neutral. Subtract Load 1 from Load 2, or vice versa, which ever is greater, it should equal the Load of the Neutral. If not, Something is running to ground. Turn Breakers off 1 by 1 till all adds up, the breaker that is off when all adds up is the culprit. If you have ground wires, clamp around each and look for any load. When I have outside recepticles, I Install the GFI on the Inside. Keeps The GFI away from the elements, and when leaving to go back Home, you can Trip the GFI on the inside, no one can use the outside. Any signs of someone staying there?

But also you didn't mention if you have a water heater that is electric? Sometimes they can cause unusual electric consumption. If you don't remember there being a breaker then turn it off and put tape over it.

The water heater is electric, but it was drained/winterized and electrically disconnected.

I turned off the mystery breaker but didn't put tape over it. I turned off virtually all of the breakers.

Pull the cover off the panel and see where the 240 circuit goes. Garage heater? Should be a 240 outlet somewhere. Do you know what a standard 240 looks like?

Yes, I need to do what you suggest and follow where the wire leads. There is a heater in the garage, but it fueled by LP so I doubt that it is powered by a 240-volt circuit. It's possible, though. (additional information: I have never used the garage heater... and I never plan to use it... my plan has been to remove it this year and to sell it).

I have a good deal of wiring experience for a non-professional electrician. I re-wired the entire kitchen myself. (so, yes, I know what a 240-volt receptacle looks like).

I would purchase an Amprobe type Current Meter...

This is a helpful suggestion. Thanks.

Any signs of someone staying there?

There were no signs of anyone staying there. Nothing looked like it had been touched, either in the house or in the garage. There were no footprints in the snow, either, which makes me suspicious of the power companies' claim that the meter had been manually read as well.

I asked about a 240 outlet because inexperienced people say, Oh you mean my range outlet? No, that is 120/240. I just rewired a 120/240 to a straight 240 and the person asked why I was putting in a "house outlet". When I showed them the front, it was, "I've never seen one like that before".

I asked about a 240 outlet because inexperienced people say, Oh you mean my range outlet? No, that is 120/240. I just rewired a 120/240 to a straight 240 and the person asked why I was putting in a "house outlet". When I showed them the front, it was, "I've never seen one like that before".

I thought it was a fair question. Maybe I don't what a 240 outlet looks like... but I have wired an electric dryer, the electric stove/range, and the wall & baseboard heaters (all 240 V).

To phrase it more correctly, there are no receptacles or other fixtures in the garage that would be 240V (that I can think of). It's a pretty simple garage without much happening. It has a bunch of receptacles on the walls, two garage door openers, and that's it. There's nothing fancy or interesting in it.

Here is an Amprobe, bid ends in 1 day, is $5 currently, shipping $22($27), shows others at bottom of page. You don't need to pay more than about $40. If you have the Money, then you might as well get an AC/DC Amprobe. Excellent for Cars, Boats, Motorcycles, any DC volt stuff. You can see drains, Battery Charging, more, Very Useful.

I thought that I would post a follow-up to this, since I figured out the problem.

The power use was actually one of the wall heaters. It's a 1000-Watt heater (1 kW x 24 hours x 31 days = 744 kW-hours) that (I've since learned) does not really ever turn off. That is, if you turn the dial all of the way to the left, it doesn't turn it off, but rather it sets the thermostat at the lowest possible temperature (~25 degrees F?). My guess is that it was not running while I was visiting last week (Jan 23) because it was a relatively warm day. When I returned (Jan 29) and turned all of the circuits on, it started running right away. My solution was to turn all of the heating circuits off for the winter.

The mysterious 30-amp, 240V circuit in the garage leads to an outdoor receptacle that I had never noticed before. Although the circuit is clearly not original, it was definitely not very recent either (the receptacle had two different wasp nests in it). My guess is the former owner installed it at some point after the garage was built in 2006. I have this circuit off now as well.

Good Deal. Also You can change breaker and receptacle to a 120 volt outlet if needed where it is(outdoor). Turn breaker off when you leave. Good you found it.

Thank you for returning with a followup. It helps us a lot in answering future questions from other users with your feedback.