Blog Post

What's the Greenest Option for Home Heating?

Heating with wood pellets, such as with this freestanding Quadrafire Mt. Vernon pellet stove at our own house, can be the greenest option, since wood pellets are a renewable heating fuel. Photo: Alex Wilson. Click on image to enlarge.

I've always gotten a lot of questions from friends, neighbors, and casual acquaintances about energy issues, and those questions picked up dramatically when I started writing this column two-and-a-half years ago. Beginning with this week, I'm going to devote an occasional column to answering some of these questions. (Feel free to e-mail questions to me:

What's the greenest option for heating my home?

This is actually a surprisingly complex question. My first answer is that the greenest heating option is that which uses the least. In other words, reduce the amount of heating that's required by carrying out energy conservation improvements. Less is better no matter what the type of heat. I tend to include passive solar features with energy conservation--by introducing solar heat through south-facing windows, we reduce the need for other heat sources.

But that answer is a bit of a cop-out. In our climate (cold!), we almost always need to provide supplemental heat to keep our houses comfortable. That's especially the case during very cold weather, which we're experiencing this week. Nighttime temperatures have dropped well into the minus-double-digits (Fahrenheit) in Vermont over the past week. Electric heat?

With an extremely energy-efficient house (R-40 or more in the walls, triple-glazed windows with two low-e coatings, and very tight construction), electric heat can be the greenest option. Electricity? Yes, electricity...but only if the heating loads are very small. With a very low heating load, it's possible to generate the electricity needed using photovoltaic (solar electric) modules either mounted on the roof or ground-mounted.


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If I were building a new house today, it would be superinsulated and heated with a high-efficiency, mini-split, air-source heat pump that I could power with electricity generated on the roof. Even if I couldn't afford the PV panels right away, I might opt for electric heat anyway to avoid the need for combustion in the house (an indoor air quality and safety concern) and to enable easy conversion to solar-generated heat down-the-road.

Wood pellet heating systems

From an environmental standpoint, avoiding fossil fuels is a great goal. If we can't heat with solar-electricity (or if our heating loads are too large to make that practical--which will be the case with most existing homes), then I'd recommend wood pellets.

Wood pellets are clean-burning and renewable. Yes, they emit carbon dioxide (a greenhouse gas that causes climate change), but trees sequester carbon dioxide out of the air as they grow--converting it into above- and below-ground biomass. So, as long as trees are grown sustainably--meaning that trees are harvested only as quickly as replacement trees are grown--wood pellets (and cordwood) are "carbon-neutral."

A downside to heating with wood pellets is that electric blowers are used. One of these blowers introduces air into the combustion chamber and another delivers warm air to the room. The result of fan-assisted air supply is very clean combustion--emitting significantly less air pollution than wood stoves that burn cordwood. But those blowers are noisy and we should consider how that electricity is made. Solar-electricity is great; coal-generated electricity isn't.

For central heating, a pellet boiler should be considered. Burning pellets heats water that is circulated through baseboard radiators just like oil- and gas-fired hydronic heating systems. Be aware that advanced pellet boilers (most of which are made in Europe) are expensive. With a pellet boiler, pellets can be bought in bulk, avoiding the plastic bags that most wood pellets are sold in. One of the biggest frustrations I have with my pellet stove is the large number of plastic bags that accumulate.

If central heating is not required, a pellet stove makes a good heating option. Pellet stoves, though, require filling by hand, while most pellet boilers are more automated. This limits the practicality of pellet stoves for homeowners who are away for more than a couple days at a time during the winter. Be aware that pellet stoves are noisy (from the fans) and they deliver their heat by forced convection rather than radiation. It just isn't as pleasant to sit in front of a pellet stove as it is in front of a wood stove (where I am as I write this).

In rural areas and for homeowners with their own woodlots, wood stoves are an okay option, as long as a modern, relatively clean-burning woodstove is used. Use only dry wood to minimize pollution from wood burning.

Next week, we'll dig into heating options a little deeper, covering systems that use natural gas, propane, and fuel oil.

In addition to this Energy Solutions blog, Alex contributes to the weekly blog BuildingGreen's Product of the Week, which profiles an interesting new green building product each week. You can sign up to receive notices of these blogs by e-mail--enter your e-mail address in the upper right corner of any blog page.

Alex is founder of BuildingGreen, Inc. and executive editor of Environmental Building News. To keep up with his latest articles and musings, you can sign up for his Twitter feed.

Published January 25, 2011

(2011, January 25). What's the Greenest Option for Home Heating?. Retrieved from

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January 25, 2011 - 2:30 pm

Theoretically, wouldn't a solar or wind powered geothermal heat pump be the most green heating system? (Free heat/cooling source (earth), only need electricity to run heat pump)
My question is can solar or wind provide enough energy to run the heat pump, and two is it economically practical?

January 25, 2011 - 1:34 pm

For me the equation has shifted to this: In the (past) era of cheap affordable energy we could afford to rely on mechanical equipment (machines) to provide comfort. As we transition to an era (and a realization of) damaging and expensive energy we should rely on the building itself to assure comfort.

Thus we seek a "net gain" equation with our glazing and a miserly "thermos" effect from our building envelope.

The challenge is in converting our now obsolete housing stock to this new formulation.

January 25, 2011 - 1:06 pm

Thank you for your blog. Where is the masonry stove? Cheers Mike

January 25, 2011 - 12:48 pm

The sun's energy is the best way to heat a home. Passive energy efficient design comes first. Since additional heat is often needed stick with the sun's free energy. A simple solar thermal evacuated tube system with a few low temp radiators will be the perfect suplement for a home with a low Btu load. If you need more heat consider a radiant system or low temp baseboard. A backup boiler may still be needed but most of the day the heat load can be met with solar. We are in Maine and are experiencing the same cold weather as VT. Our clients will tell you how solar heating is saving them money and cutting their enviromental impact.

January 25, 2011 - 12:38 pm

Hi Alex,
I always look forward to reading your blog, because everything you write is so informative. I do have a question though -- I'm not familiar with pellet boilers, but if they are like pellet stoves then I would assume they need to be tended to on a regular basis. How long can a pellet boiler be left unattended? From a practical perspective, anything that involves my having to look after it on a regular basis is unrealistic. I have enough to do around the house -- not to mention what happens at night? Do you wake up to a freezing cold house? -- Just curious, because I think the idea is intriguing.

January 26, 2011 - 4:26 am

If starting a fire twice a day at minus 40 is a chore; perhaps you are not ready for a sustainable building or lifestyle. Passive solar heating and cooling is job one of design in ANY climate. This DOES NOT include an expensive geothermal HVAC system. "less is better" may work on an existing structure, but is just silly when designing a new house.
Here are a few tips when building.
Is there a basement? These are gold mines for builders, while having little value for the owner.
Use natural wood frame windows and doors and wooden doors...and NEVER paint them. Linseed oil and wax is how you preserve wood.
Does it face south.
Is there enough thermal mass to actually produce a passive solar home. Most passive solar homes I see designed don't come within a country mile of enough thermal mass.
Is there a septic tank or sewer connection. If there is, your designer did not go the sustainable route

Find a designer or architect who has rejected modern energy guzzling building paradigms and opted for a pre-fossil fuel starting point. One who understands life cycles in natural building; and one who can speak eloquently on the positive lifestyle changes required to either build or live sustainably.

January 25, 2011 - 3:34 pm

A few quick responses to some of these comments:

Cathy, most of the advanced pellet boilers (like Froling and Tarm) are operated with augers that automatically feed pellets from large bins or hoppers. These storage units are filled by bulk pellet delivery trucks. The infrastructure isn't available everywhere, but I think this will become more common as we move forward.

Matt, I'd love to see active solar space heating become widespread. Do you think these systems are trouble-free enough to expect widespread installation? (I suppose they aren't much more complex than those Froling and Tarm pellet boilers!)

Mike, I like masonry stoves and think they have a role to play. Friends of mine with masonry heaters, though, get tired of starting all the fires--since a small fire is burned intensely then goes out. But for the right situation, this is a great option.

Jamie, I agree with you. My top priority is getting heating loads down so that with some passive solar gain, very little heat has to be provided by mechanical systems. In those situations, the reliability of mechanical systems becomes less important. If the oil boilers in our New England Victorian homes fail in weather like we're having and they can't be fixed quickly, people have to move out or face hypothermia. If a mechanical system fails in a superinsulated house, the temperature will drop, but probably not to dangerous levels. I agree that we have a huge challenge with existing houses.

Chris, ground-source (geothermal) heat pumps are a little more efficient than the mini-split air-source heat pumps I touted, but not much. Long-term testing of ground-source heat pumps is showing that the performance drops (as the ground temperatures change), and these systems are very expensive (and ecologically disruptive) to install. In my book, a ground-source heat pump, today, is a hard sell over a mini-split air-source heat pump. I'd go for the less expensive air-source product.

Great comments all! -Alex

January 31, 2011 - 6:31 am

Is there any idea what capacity of production of wood pellets could be maintained in a sustainable manner? I mean, if this idea took off and all new houses were built with wood pellet stoves/furnaces, how soon until production could not meet demand? Just curious. BTW, love the series.