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I just purchased my house a few months ago. The house has both a 2 zone natural gas burner with baseboards for heat and 6 Mitsubishi Mr. Slim units that I can use for either A/C or heat. I am not sure which would be more efficient and less costly to use for heating my house this winter.

I started out using the Mr. Slims, but when it got colder I decided to shut them all down and use the gas burner. I just got my first bill since then and it was much higher than I was expecting. So I am now second guessing my decision. Any insight that anyone could provide would be greatly appreciated.

EDIT: Thank you for your comment Tester101. That partially answers my question. An HVAC professional that inspected my system told me that it would ALWAYS be better to use the Mr. Slims, and I found that hard to believe. So I was wondering if others would say the same on here.

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You'll need to provide much more information to get a useful answer Gas cost, electric cost, size of house, model numbers of both units, average outside temperature, target inside temperature, etc., just to name a few. –  Tester101 Dec 9 '13 at 15:08
    
Sounds like your best option is to run the experiment, except do it carefully using either a billing cycle or a self-read of the meters involved. Online temperature graphs can help you determine which measurement intervals are relevant. Post back with results! –  Bryce Dec 9 '13 at 21:31
    
Before we go too far down this road, a second thought occurs - depending on the construction and especially insulation of your house, if you don't use the gas heat at all (you say baseboards so I assume hot water boiler and baseboards) you could freeze the heating circuits - and THAT would cost a lot more to fix than the fuel price differential... –  Ecnerwal Dec 10 '13 at 4:38
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You'd need to do some math. Namely the cost of the energy source * the amount of energy needed for each method. The amount of energy needed will depend on the efficiency of each heating method.

It's not an easy calculation by any means, but it's definitely not answerable without those details.

In general, Heat Pumps tend to be one of the more efficient option these days.

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And to make it more difficult, the answer probably changes with temperature as well as price per therm and price per KWh - most heat pump units have a lower efficiency as the temperature drops, and a point beyond which they are useless (where the gas obviously wins.) If your climate never gets that cold, it won't happen - if it does, it will. In the meantime, you do have the pragmatic option available - try each for a billing cycle, though you need to keep track of at least the average temperature over each billing cycle for a good comparison. –  Ecnerwal Dec 10 '13 at 1:15
    
@Ecnerwal ya know, there's probably a product idea out there...a thermostat that can be programmed with current energy prices and can then switch between devices based on a formula that combines that with the outside temperature...free idea for the taking! –  DA01 Dec 10 '13 at 3:28
    
The capital cost of many modes of heating (both in direct money and in more money involved in the space they occupy) makes this an idea that's not very likely to fly - though among the home-automation smart-house crowd it should be an easy software tweak. Air-source-heat-pumps in cold climates are really the only common example - in warm climates there usually isn't "other fuel" backup heat (just electric resistance, at 3-4X worse efficiency.) As a computer guy, I want my house systems pretty dumb, all told; I don't want hackers and/or glitches controlling my house! –  Ecnerwal Dec 10 '13 at 3:41
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