Air sealing/tightness + Good insulation. Then use Air Source Heat Pumps for heating and cooling.

In addition to the well insulated house Mark mentions, good windows and doors, of course. We have found that a well insulated basement (unfinished) and a tall, well insulated attic create an envelope that buffers our house from extremes in winter or summer. Our power was out for 10 hours yesterday beginning at 3 a.m. due to an ice storm. We lost two degrees in the house during that time. The floor in the basement was actually warmer than the air in the house from the steady temp of the earth. But not everyone lives where basements are possible.

+1 to all of above and reiterate air sealing. Insulation can't perform at rated capacity if air is leaking around it. The good thing about air sealing is it's easier to measure than insulation. Insist on code minimum or better blower door test results.

Well...don't you think it depends on:

--Average winter temperatures and heating degree days

--Length of "winter"

--Locally available fuels and rates

The ideal heating fuel and source in Atlanta is hardly the first and best choice in Bangor.

Right location matters. But OP specifically asked for an alternative to gas or solid. That leaves oil which, no one would recommend outside of a deserted area with no grid, or electricity.

Electricity would mean heatpump nearly anywhere.

I am counting Propane as a gas (and generally not recommended too many places either).

Wood? Electricity? Solar/air? Solar/hydronic? Cow dung? . . .

I agree that location makes a big difference in recommendations, so I'll assume you are somewhere in between Alaska and Florida :D. Depending upon how cold your climate is in the winter, I would suggest looking into a air source regular heat pump (mild winter) or air source cold climate heat pump (colder winter). I am in central PA and built a house last year with a cold climate heat pump (Mitsubishi). I have been living in the house for almost two full electric bill cycles, and am extremely pleased with the heat pump's performance. If you do decide to go this route, you may need to do a lot of research and educate yourself, because many salesmen do not know much about the cold climate HP's. Of course, time will tell if issues arise with it, but, at this point, I highly recommend a Mitsubishi!!

A wood stove heats twice. Once when you're chopping, and once when you're burning.

Most people choose natural gas if it's available. But it's not available everywhere. When I lived in Maine, most people closed off as much of their house as possible in the winter. They lived in two rooms plus bathrooms. There was often a wood stove in the main living/cooking area. Of course, as Green Designs says, this means "heat" when you spend the entire summer chopping wood for the winter. Some used oil heat as well; electric baseboard heat is often used in bathrooms. Bedrooms are often not heated at all, except by a really good big down comforter and sometimes a heating pad to warm it up before climbing in at night.

My son had 3 different houses in CT - no natural gas. They had propane so they could have a gas stove. They used oil and some electric baseboard heaters. It was very costly.

It's 2019 and new construction built to current international energy codes performs significantly better than homes of yore. Blower door proven airtightness, prescriptive insulation minimums and better windows has a significant impact on the amount of heat needed for a home.

Heat pump technology has also been revolutionized. It's very possible the right choice for Atlanta will work in Boston, maybe even Bangor.

The biggest financial argument against gas for new construction is the added infrastructure costs. The monthly, minimum service fees from the gas utility also hurt it's comparison to electric appliances. All-electric appliances are cost competitive and often cheaper to operate than gas.

Burning things inside will always be risky for indoor air quality and when prominent canadian building scientists write burning wood indoors requires opening a window or yet another make-up air system, it's time to question combustion.

If you want a real alternative, how about compost?

"...Heat pump technology has also been revolutionized. It's very possible the right choice for Atlanta will work in Boston, maybe even Bangor..."

"...air source cold climate heat pump..."

Can someone comment a bit more specifically about the performance of heat pumps (air or ground source) and colder climates?

Check out NEEP for more info on cold climate air source heat pumps (ccASHP)
https://neep.org/initiatives/high-efficiency-products/emerging-technologies/ashp/cold-climate-air-source-heat-pump

Greenbuildingadvisor has lots of info on them, this article covers a bunch of bases: https://www.greenbuildingadvisor.com/article/bruce-harleys-minisplit-tips

I live in central PA and am just a homeowner, but I do have an air source cold climate heat pump. Last year with a new build, I bought the following for heating/cooling:

• Mitsubishi - MPV AA36AA 7 36,000 BTU multi position indoor air handler
• Mitsubishi - MPUZHA36NHA5 (3 ton) Hyper-Heat technology variable speed outdoor heat pump
• Mitsubishi - MEHI0MPL (two stage) I0kw electric heat package

House is two story, little over 1900 sq. ft., full glass French doors, 13 windows, two half glass exterior doors, standard insulation, unconditioned basement, and hybrid heat pump hot water heater.

My first full month (electricity bill wise) living in the house was from about November 17-December 17. This period was colder than our normal temps for that time of the year, and I did a TON of laundry (electric dryer, of course -- I had stored a bunch of clothes, and washed everything when moving in). The bill was $141 (I think the electricity was around 11.5 cents, which was down from earlier in the year).

Weather became milder (more average temps) I am now 28 days into the electricity bill, and the balance is $101.07.

I was extremely hesitant to buy a heat pump, because I only ever knew "traditional" HP's in this area which are only used for AC and a tiny bit of heating during very mild weather. On paper, the cold climate HP's looked great, and I decided to take the leap. So far, I am VERY HAPPY with the decision! The Mitsubishi unit I have is still able to product 80% capacity at -13. Last year, I did my own figuring with current oil/electricity prices, and guessed that, in my situation, I would be:

• Any temps down to low 20's, saving money with HP over oil.
• Between low 20's and mid teens, HP and oil about the same.
• Low teens and below, HP costs more than oil.

Of course, this varies incredibly based on oil and electricity prices, but it was one of the pros/cons lists I did.

The company that installed the system said they would never expect the heat strips to ever have to kick on, but they are there, just in case.

The problem with geothermal (ground source heat pump/GSHP) is its cost. Now that cold climate air source heat pump's have improving efficiencies, and are capable of heating in sub-zero temps, it becomes hard to justify the cost of drilling a well.
There's a coalition of geothermal companies here in the north east that all are committing to a ~$23,000 installed and commissioned GSHP HVAC system cost.
A ccASHP would come in about half of that.

The GSHP will heat better below 0, but how often does that happen, and much will that save you?
I did the calculations for myself last year and came up with around $300 a year savings over air source. A 30+ year payback.

A ground source heat pump is a good solution for a commercial application. It is too costly in most cases for a well insulated residential house.