There is at least one cold truth about your heating system; it will never die at a convenient time. While it would be nice to have the leisure to thoroughly research all the latest technologies before buying, Murphy’s law of Maine winters suggest your boiler is most likely to be pronounced terminal in late November, just as the last leaf floats to the hardening ground.

That’s why this guide to the most common sorts of heating systems (and a few up and comers) is designed to help you if you have to move fast.

But even if you have more years left in your system, it’s never too soon to start thinking about the next – and greener – means of making it through a Maine winter. (Did you hear the Farmer’s Almanac is predicting a cold, wet one?) This isn’t a statistic we like to boast about at Source, but Maine already lays claim to the highest per capita energy usage in New England, according to the U. S. Energy Information Administration.

Ideally a heating system lasts 20 years, so these aren’t choices one should make lightly, or with the short term in mind. If you’ve had an oil system, the temptation to stick with it might be high from a price perspective. It’s not good for the environment, but it’s familiar, and right now, heating oil costs just a smidge over $2 a gallon, almost half what it was in March of 2014. But will it stay cheap for long? It has already crept up from $1.88 in September.

“That’s not really a bet I’d make,” said Dylan Voorhees, Climate and Clean Energy project director of the Natural Resources Council of Maine. He conceded that cheap oil means “the math gets trickier” when comparing systems.

There’s a caveat though, as Voorhees points out. “Heating systems are a really important part of your heating equation, but it is important to look at the whole house, particularly if you are thinking about making a large investment. Switching from one fuel to another could have important environmental benefits. But it is not a green choice if you are still wasting a lot of it.” In other words, before you bother to upgrade weatherizing with air sealing and insulation is crucial.

Here are some of the pros and cons of the main methods of heating available today. File it away, because you’ll need it one of these days.

FUEL OIL

Renewable? No

1111336_857603 oil.jpgFor decades, Mainers have relied on fuel oil No. 2. As recently as the winter of 2005-2006, 80 percent of us heated with it, making it the old reliable. But slowly, steadily, we’ve started to shift away from it. The latest figures from the U.S. Census Bureau’s American Community Survey have 61.7 percent of Mainers reporting that they use oil to heat their homes. “Where has that 20 percent gone?” said Lisa J. Smith, senior planner with the Governor’s Energy Office. “Not to just one fuel source.” Electric, propane and wood have all seen bumps as a result.

Price has most often been the driver, but heightened environmental awareness – and a desire to get off foreign fossil fuel imports – have certainly had an impact. Sales of oil furnaces in the U.S. dropped radically in a ten-year period ending 2012, to about 30 percent of what they were in 2002. And as climate change continues to affect how we live and consumers seek more sustainable sources, those sales are expected to continue to drop.

PRO: Oil burns well, which is to say, hot. If you shop for a new system, you’ll hear a lot about Btus. That stands for British thermal unit, and it refers to the amount of energy (heat) generated per gallon. The higher the Btu number, the more heat generated per gallon. Heating oil produces 138,500 Btus per gallon. By comparison, propane systems produce 91,333 Btus. Stands to reason that your oil heat is better, right?

CON: Wrong. Oil systems are less efficient than propane, although the newer and better the equipment, the better oil will perform, up to 80 percent efficiency on new systems and even 85 percent on Energy Star. The rating is known as AFUE, an ungainly acronynm for annual fuel utilization efficiency. What does that mean, precisely? It means that 80 percent of the fuel is actually heating the house; the other 20 percent is lost (up the chimney and out into the air for instance).

THE LOCAL INDEX? No oil, or petroleum, is produced in Maine, although the United States is producing more crude oil than in the past and is expected to continue to do so in the next few decades, according to the U.S. Energy Information Administration.

THE MYTH: Many of us reassure ourselves that at least oil doesn’t involve fracking, which is associated with problems all over the United States, including earthquakes in areas like Ohio, not hitherto known for seismic disruptions. But the picture isn’t that clear. “When you talk about the environmental costs of digging oil and natural gas out of the ground, they are also pretty similar,” Voorhees said. “The extraction of oil and gas and propane are really closely bundled together.” These fossil fuels tend to be found close to each other in the ground and thus fracking produces oil as well as natural gas.

GEOTHERMAL HEAT PUMPS

Renewable? Kinda sorta.

1111336_857603 heatpump.jpgThe Environmental Protection Agency (EPA) loves geothermal heat pumps, which are clean, cost effective and the most energy-efficient means of controlling temperatures, but they can’t run without some electricity.

Ten feet below the surface, temperatures are consistently between 50 and 60 degrees (Siberia, an exception, Fort Kent, not). Geothermal heat pumps transfer that heat into a building. While this is a great technology, geothermal heat pumps, and actually just heat pumps in general, rank high on Ctu scale. That’s the Confusion per thermal unit, meaning how puzzling it is to most of us that transferring soil (or water) temperatures somehow warms up houses. (We made that up, by the way.) It’s challenging to gauge how many Mainers are using geothermal heat pumps since this is not a category surveyed by the Census Bureau. Its 2015 estimates show 11,000 households in the state heating with “other fuels,” with geothermal falling into that catchall category. “It is a tiny slice of the pie right now, but it is growing,” Voorhees said. Notably, “other fuels” included only 2,700 households in 2005, so use of alternative energies is growing in the state.

PRO: They also function as air conditioners in summer. Why don’t we all have them? See below.

CON: The upfront expense is the biggest. You are digging a very large trench in the ground, and putting in some serious infrastructure. You can’t pick this system up at Lowe’s. “It is cost prohibitive unless you are building a new home,” Smith said. Retrofitting a drafty old Maine house to the degree where geothermal makes sense is daunting. “I have been told it just isn’t a feasible thing,” she added. But for new construction, geothermal is the bomb.

THE MYTH: It’s too cold for geothermal in Maine what with the frozen ground and all. Not true. It’s not Siberia, at least not 10 feet down.

AIR SOURCE HEAT PUMPS

Renewable: Mostly.

1111336_857603 airpump.jpgThe principle of an air source heat pump is very similar to a geothermal heat pump, but more electricity is involved in running them (as with air conditioners). The cleaner your electricity source, the better you can feel about your heat pump. “A heat pump is a really good choice,” Voorhees said. “The only thing better than using a heat pump is using a heat pump while running solar on the roof to drive the electricity for your heat pump.”

If your neighbor is jawing on about his heat pump, it’s most likely an air source system, whereby thermal heat from the air (even when it is cold, yes, that’s confusing, but trust) is transferred through a heat exchanger and warms the house.

Heat pumps have been “transformative in Maine’s market,” said Smith of the Governor’s Energy Office. The increase in their efficiency over just a few years has been “phenomenal,” Smith said. Famously, Gov. LePage is a fan, and as he’s demonstrated with solar, he’s not usually one to embrace alternative energies wholeheartedly. But last year, he installed heat pumps in Blaine House.

PRO: “They sell themselves,” Smith said. One person in a neighborhood gets them and then talks them up. “That is how the success of them has moved forward.” They rely on electricity, but “the source of electricity in Maine is very clean,” said Dana Fischer, residential program manager for Efficiency Maine. “It’s one of the cleanest states.”

CON: While there is an almost magical aspect to how they work, extracting heat from the air, heat pumps do require electricity to run. (On the other hand, “everyone has electricity and it’s not like another type of fuel has to be delivered,” Smith said.) Some people complain of a “draft” around the heat pump itself, due to the movement of the air. A backup system, whether it’s a pellet stove or a fossil fuel-run furnace, is generally necessary.

THE MYTH: Cold places aren’t suitable for a technology that depends on air transfer. “That was the general opinion of Mainers,” Smith said, until quite recently. “That was my reaction – ‘What, are you kidding?’ ” Now homeowners all over the state are putting them in. “Even near the Canadian border. As long as it is calibrated correctly, the heat pump takes the load and then the furnace is the backup,” Smith added. Another myth: that heat pumps will freeze and stop working, provoking a terrifying and chilly disaster. Not so, said Fischer, who uses a heat pump in his own home. “It is not like anybody is going to freeze,” Fischer said. “It is just that the house goes down to the mid-60s.” A boost from one of his other heating systems gets it going again.

SOLAR

Renewable? Yes

1111336_857603 solar.jpgThe sun keeps on shining and if someday it doesn’t, we’re all dead anyway. It’s the ultimate renewable energy. How can you use it to heat your house? Mainly, build a Passive House, with super thick walls and the kinds of windows that trap the heat. Then you’d need a supplemental heat source only to get you through the chilly days. Photo voltaic panels on the roof could even generate the electricity to run say, a heat pump. It’s the green dream, really. “Then you get an electric car too and you have enough panels to run it from them and that is the future,” Voorhees said.

Plenty of Mainers have joined the sunshine wave sweeping through Maine, installing solar panels or joining in solar farms. Statistically speaking, they’re probably using solar power for electricity or to heat hot water rather than to heat their homes. Solar can heat ordinary homes (not just Passive Homes); in what is called an active solar heating system, it warms a fluid (water, antifreeze) that circulates through a home – the most common way would be a radiant system. It’s an expensive conversion and again, more suitable for new construction. As of 2015, only 604 households in Maine heated with solar power, according to U.S. Census surveys, up from 451 the year before. It’s a confusing category because it doesn’t distinguish between radiant solar heat and Passive Houses. Smith of the Governor’s Energy Office couldn’t make the distinction, either. Maybe in the future the Census Bureau can add Passive House to your questionnaire.

PRO: Endless.

CON: It’s not cheap – until you factor in your heating costs, or lack thereof. And because the technology is still fairly new to America, only a handful of local architects and builders are working on Passive House models. But those who are, like Ecocor of Searsmont, keep their materials green and local wherever possible (like Maine wood).

MYTH: What about those short days in the winter? “We don’t even have seven hours of daylight in the winter!” Smith said. Doesn’t matter; passive solar construction can work around that.

WOOD

Renewable? Yes

1111336_857603 wood.jpgIn the 1940s, wood was still a major heating source across the country, particularly in the Pacific Northwest and the South, according to the U.S. Census Bureau. More than half of Mainers (53.5 percent) heated their homes with wood then, but by 1950, as fuel oil became more commonplace, that number dropped to just half that, and fuel oil rose to 50 percent.

Wood has made a comeback in recent years, probably due to the advent of high-efficiency wood pellet stoves, and modernized cordwood stoves that use catalytic combustors to reduce emissions. Between 2005 and 2015, the number of Mainers who reported using wood as their heat source nearly doubled, up to 71,000 households.

PRO: It’s home grown, mostly, and if sustainably harvested and burned in efficient equipment, a far greener choice than fossil fuels. And the energy burned in producing cord wood is minimal, even less than the energy used to mill wood pellets.

CON: Although the EPA does publish a list of stoves certified to meet emission limits for particulates, no efficiency standards exist yet, which makes them slightly less user friendly for shoppers who want to go green. Still, “an EPA-certified wood stove is much cleaner than what you could get in your parent’s generation,” Voorhees said. “It can be a good choice.” (He takes issue with some Maine power plants that burn wood; “they are really inefficient.”) Cordwood stoves require chimneys to vent combustion gases, which typically add costs to the systems.

THE MYTH: Trees take a long time to grow, so how can nature possibly keep up with human demand? That argument could hold water somewhere, but not in Maine, which has moved in and out of first place in U.S. Forestry Service surveys of the most wooded states in the union.

WOOD PELLETS

Renewable? Yes

1111336_857603 pellet.jpgYou don’t get much more local than this form of fuel, with four manufacturers producing wood pellets in Maine, using mostly Maine-grown wood. The Energy Information Administration reports sales of pellet stoves grew rapidly between 2005 and 2008, which is when most of Maine’s pellet mills came on line.

PRO: Require much less care and feeding than a cordwood stove and burn with greater efficiency. “You have to fill your fire box three or four times a day” with cordwood, said Matt Bell, the past president of the Maine Pellet Fuels Association, and owner of Northeast Pellets in Ashland, the first pellet mill built in Maine, in 2004. “With pellets, you fill your stove once a day.” Can be vented directly outdoors.

CON: Supply and demand issues can be even more pronounced than with other fuels. Mainers often have multiple heating systems. “As I say, they run their own little hedge funds,” Lisa Smith said. They go back and forth among several different types of heating systems, burning whatever is cheaper at the moment. “They look at the prices and they say, ‘I’m going to buy more oil this year’ to try to minimize their heating costs.” When that happens, the pellet industry takes a hit. The state’s pellet manufacturers have seen their fortunes rise and wane on the backs of oil prices. Case in point, Corinth Pellets in Corinth, which let nine workers go last January and cut shifts to three days a week from seven.

“Wood heat is in the renewable basket,” Voorhees said. “Although unlike solar, it does have important emission effects.”

THE MYTH: When it comes to heating with wood, a lot of Mainers have been stuck in a 1970s and ’80s mentality, namely that the emissions contribute heavily to air pollution. “Acid rain is actually the result of coal burning in the Midwest and that coming our way, versus burning wood,” Smith said. Moreover, the increased efficiency of pellet stoves means far fewer emissions. But this is still a relatively new technology. “When we started in 2004, it seemed as if I spent more time educating people on what wood pellets are and how they worked than I did actually making them,” Matt Bell said. “We have made a lot of progress there, but there is still a lot of ground to cover.”

PROPANE

Renewable? No

1111336_857603 propane.jpgThe percentage of Mainers using propane, which is extracted from natural gas or refinery gas streams, has increased in recent years but is still relatively low, 9.3 percent, according to Smith of the Governor’s Energy Office. “It has gone up a little as heating oil has gone down a little.” Put it this way, about 17,000 more Maine households were using propane as a heating source in 2015 than there were in 2005.

PRO: Propane is a cleaner fuel than heating oil, emitting lower units of carbon per unit of heat. It can also reach people in rural areas the way natural gas can’t.

CON: In terms of Btu, propane doesn’t have the oomph of fuel oil. “The thing about propane is that it fluctuates at least as much as the rest of the commodities and tends to be more expensive because it doesn’t have as many Btus,” Efficiency Maine’s Fischer said. And Smith recommends “a little more due diligence with propane,” because the price is not regulated. “The market price is the market price. It pays to shop around.”

THE MYTH: The tanks. They’re not pretty and they make a lot of people nervous. Like that they’re-going-to-go-boom nervous. “Do you see propane explosions in Maine?” Smith asked. “No you don’t.” Here’s the thing, Fischer said: Heating oil is a carcinogen, yet people regularly keep 275 gallons of toxic liquid in their basement. “It is a little bit of pick-your-poison.”

ELECTRICAL

Renewable? It’s complicated

From a sustainability perspective, this category is hard to parse for two reasons. The New England grid includes distinctly non-sustainably run power plants (like coal and natural gas). Also at this point, heat source surveys don’t reflect what proportion of households use electricity to run heat pumps, base board or even space heaters. Mainers heating with electricity represent a small slice of the overall population according to the latest Census figures, but it’s on the rise, up more than a percentage point to 6.4 percent in 2015. (That bump could be directly attributable to the new users of heat pumps, like LePage.)

PRO: Generally speaking, what Maine contributes to the New England power grid is fairly green, although we operate as a region, with all states feeding into it. (If you’d like to support green electric power production in Maine, you can request the Maine Green Power option when ordering electricity. Visit the Maine Public Utilities Commission’s website for more information.)

CON: The price. Efficiency Maine estimates that the annual heating cost for a home warmed by electric baseboards is more than twice that of oil and, at current prices, about $1,000 more annually than the next most expensive heating source (a propane furnace).

NATURAL GAS

Renewable: No

In most cold parts of the country, natural gas is the dominant heating fuel. Not in Maine. While it might seem as though half the people you know made the switch to natural gas in recent years, when it was relatively cheap and oil was expensive, that’s not true. According to the most recent census surveys, about 38,000 Maine households out of 545,000 use natural gas.

The difference between burning oil and gas is something Voorhees gets asked all the time. “We are not in the position to tell people that switching to gas is a greener choice,” he said. Nonetheless, “The direct emissions from your boiler or furnace are going to be lower from gas.” He’s lumping propane into this equation as it too is a gas, albeit a wet one. “The emissions from propane and natural gas are really similar.”

PRO: It does burn cleaner. “It has a lower carbon footprint when you burn it, compared to oil,” Dana Fischer of Efficiency Maine said. “But some people are concerned about fracking, so they don’t want to go with natural gas.” As Voorhees pointed out, oil and propane are also often associated with fracking.

CON: “It’s all dirty, and it is all contributing to a warming climate, and we need to move off those fuels,” Voorhees said. “If you are looking to move toward sustainability, then picking between dirty fossil fuels is the wrong question to ask.”

THE MYTH: Haven’t we all heard that natural gas pipelines are mere blocks away from us and will soon be available to us? Not so. For the majority of Mainers who live in rural areas, natural gas is never going to be an option because it doesn’t make economic sense for the natural gas companies to lay pipelines to rural areas.