This is a complicated question with no easy answer.

In order to answer it, you would need to research the price of propane per gallon vs the cost per killowatt hour plus taxes by your electric utility.

And while propane typically will cost less to provide the same amount of heating energy, that is not the whole story.

Price per gallon of propane is market driven and can fluctuate wildly during the season and from year to year. If you buy it in the off-season, you can save, but when you need it in winter, you must pay whatever the market will bear.

Electric rates, on the other hand are largely fixed and regulated by public utility commissions.

Electric suppliers will also give price breaks to those who construct (insulate) their homes to EnergyStar standards and you can set up budget payments with your electric utility whereby you pay a fixed monthly rate all year and don't have large heating bills in winter or large cooling costs in summer.

With propane, you will still need to pay a separate electric bill at non-discounted rates.

So do your homework. Call your electric utility and ask them to tell you about their EnergyStar programs. Call you propane supplier for current prices then research the historic price of propane over the years.

Luck.

In our area, Maryland, The energy star program is about insulating the home, Good windows and doors. There is a summer rate and a winter rate.
We installed a Trane system that is an electric heat pump that provides heat however when the temp. get down to 39 degrees, it switches over to the propane furance. It is all one neat little unit and it is 15 seer. We put in a 500 gallon propane tank and buy in the summer. It is almost half the price as it is in the winter. Propane is warm and being from New England, you'll get a warmer heat with propane when the temp drops! Our house is almost 3600 sq feet and a full tank lasts from October to April and we have our hot water, stove/oven, grill and heat all on one tank. Good luck with your choice!

We installed a Trane dual unit as well. I believe this is the best of both worlds because you don't have to totally rely upon propane but you have it available when the temp drops. Our house will be finished in a few weeks so we will be able to test it out this winter.

It's not a simple "A" or "B" answer. YOu're going to have to do some homework.

You'll need to know the price per gallon of propane and price per kilowatt for electricity. Then, you'll need to compare different furnace packages and their efficiencies. The more efficient a furnace is, the costlier it is, so there comes a point when gaining in that department becomes too long of a payback period. You'll also need to figure out how well you're going to insulate, and if possible, insulate beyond the "required" level. Insulation is the cheapest heat/cooling that you can buy, because it keeps that warm/cool air that you've paid for inside your dwelling. In MI, I'd think you'd be 2x6 construction, and if not, it's worth it to upgrade to it.

I know oil is more efficient than propane comparing btus. Meaning, even though propane seems cheaper it isn't because each gallon of propane delivers less heat than a gallon of oil. Electric is WAY more expensive than propane or oil here, but your rates may not be what ours are.

I would contact a energy auditor to help your analyze the options. Also remember that some systems cost more to purchase and install so you need to factor in the extra cost of the system to determine the payback period. This is way too complicated for amateurs to do on their own.

Propane is so expensive it is NOT used to generate electricity.

That might be a clue.

Propane - 92k btu gallon. Typical rate is $2.50. So 100k btus costs $2.70 or so. Assuming a 95% efficient furnace and you are just under $3.

Electricity - 3.3k btu/kwh. Typical rate $.10. So 100k btu costs $3.30 or so. All electric heating strips are 100% efficient.

So at average rates, they are pretty close - maybe electric is 15% higher. With electric you can add a heat pump - but that costs $$ since you probably don't need a/c. If you need a/c, then the extra cost for a heat pump is minimal.

If you can get propane for much less than $2.50 or your electric rate is much less than $.10, it can really change the situation.

Either way, I am going to do the impossible and guess - $500 a month. It is an insanely wild guess. Build you house tight and with good solar gain and it might be $200.

There are other options. Geothermal has a 30% tax credit and uses electricity. It would probably be $50 a month with a tight house. There is oil, wood, pellets etc. - none of which are recommended (oil) or maintenance free - other options.

Jfelen - 39 degree is way high. I believe MD has higher than average electric rates but you would definitely save money going lower. With propane, 25 is common. Your electric rates may change that to 30 but no way is 39 the best economic answer. Now - you might like the warm air and that is a different issue. I would try inching down a few degrees and see if you don't mind it. I'm at 35 (with NG) and I've never noticed unacceptably cool air (but that's me and my wife).