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Musings of an Energy Nerd

All About Wood Stoves

It might make sense to heat your home with wood — even though firewood is the least convenient of all common fuels

Yes, the glow of a wood fire is a cheery sight on a chilly day. But heating with wood is a lot of work.
Image Credit: Erica Breetoe

If you’ve been heating your house with wood for years, you probably don’t need to read this article. By now, you know all about the disadvantages and inconveniences that accompany wood heat, and yet you still heat with wood — either because you genuinely love wood heat, or because you love the low cost of the fuel. If you haven’t burned down your house by now, you may even have figured out how to install and operate your stove safely.

This article is addressed to a different audience: those who are thinking about buying their first wood stove.

Forget about the warm glow — and get ready for lots of schlepping

For some homeowners, especially those who haven’t lived with a wood stove, wood heat has romantic associations. Veteran wood burners know better, however. As a document from the Cornell University Cooperative Extension points out, firewood “is one of the least convenient sources of heat, … requiring time and considerable effort to fell and split trees, move wood into dry outdoor storage for at least a year, transport wood indoors, maintain an effective woodstove fire, and keep the system cleaned for safety and efficiency.” I’ll add another disadvantage: if you heat with wood, you’ll be tethered to your house all winter. You won’t be able to go away for the weekend unless your house has a backup heating system to keep your plumbing pipes from freezing.

Wood heat makes the most sense for:

  • Homes in rural rather than suburban or urban locations;
  • Homes equipped with a woodshed or outbuilding where several cords of firewood can be stored;
  • Homes located in areas where firewood is cheap or can be cut for free;
  • Compact two-story homes rather than stretched-out single-story homes;
  • Homes with an open floor plan rather than homes with many small rooms and many closed doors.

Where does a wood stove go?

Don’t install an outdoor wood-fired boiler (sometimes mistakenly referred to as an “outdoor furnace”). These devices are notoriously polluting and inefficient. They require lots of electricity to run and they waste much of the energy value of the firewood they burn. Moreover, they are so smoky that they will drive your neighbors crazy. In many areas of the country, irate neighbors have sued owners of outdoor wood boilers, alleging that the devices represent a neighborhood nuisance.

The best place to install a wood stove is indoors, not outdoors. After all, that’s where you want the heat. Ideally, a stove should be installed in a large room near the center of your house. It needs to be installed on a fireproof hearth. Commercially available hearths are made of steel sandwiched to a thin layer of insulation. Other hearth options include brick, stone, or concrete.

The stove should be located at least 36 inches away from unprotected walls, furniture, or other flammable items. You can reduce the 36-inch-clearance rule (at least for walls) to a minimum of 12 inches by installing a metal heat shield on the wall you need to protect. There must be a 1-inch air gap between the sheet metal and the wall. The sheet metal should be attached to the wall with long screws; one-inch spacers are used to maintain the necessary air gap. (I favor using 1/2 inch by 1 inch brass or steel plumbing nipples to maintain this space; it’s also possible to use ceramic insulators sold for electric fences.) Remember that the sheet metal has to start 1 inch off the floor to allow a gap for air to enter at the bottom.

Adjacent to the hearth, you’ll need a chimney.

All about chimneys

Until the 1970s, all chimneys were made of brick or stone. Since then, however, metal chimneys have become common.

Older brick or stone chimneys were often unlined. Unlined chimneys cannot be safely used to vent a wood stove, however. If the chimney has clay flue tiles in good condition, or a stainless-steel flue, it can be safely used. When in doubt, hire a chimney specialist to inspect your chimney before you hook up a wood stove to the chimney.

If you are building your own brick chimney, don’t make the usual owner/builder errors. These include forgetting to install the clay flue tiles, and forgetting to install a cleanout door at the bottom of the chimney.

Metal chimneys are not the same as stovepipe. You only need about 3 or 4 feet of stovepipe; that’s the pipe that connects the stove with the chimney. Metal chimneys that are rated for wood stoves are double-walled. The inner pipe is stainless steel, while the outer pipe is either stainless steel or galvanized steel. Follow the manufacturer’s installation instructions when installing a metal chimney.

When it comes to elbows — either stovepipe elbows or elbows in metal chimneys — there is just one rule: you want as few of them as possible.

Whether your chimney is made of bricks or metal, it should be located in the interior of your house, not on the exterior. Exterior chimneys are cold, while interior chimneys are warm. Cold flues cause two problems: they don’t draw as well as warm flues, and they encourage the formation of creosote.

Creosote is a tar-like substance that accumulates on the interior surface of a wood-stove flue. It accumulates when flue gas components condense. There are two forms of creosote: liquid creosote and solid creosote. Liquid creosote is newly formed; you sometimes see it leaking through stovepipe joints, especially if the installer mistakenly pointed the male ends of the stovepipe segments toward the chimney thimble rather than toward the stove. Solid creosote is what you are left with when the liquid creosote dries up.

Solid creosote is flammable. If it ignites, you’ll get a roaring fire in your flue. This event is called a chimney fire. If you have a chimney fire, close all the dampers and air intakes on your wood stove, call the fire department, and get out of the house. When you’re standing in the snow looking at the top of your chimney, waiting for the fire trucks to arrive, you’ll see tongues of fire shooting skyward like the flames of a blast furnace.

Take the following steps to prevent chimney fires:

  • Only burn seasoned firewood, not green firewood. Green firewood doesn’t burn as hot as seasoned firewood. Slow, smoldering fires encourage the creosote formation.
  • Don’t overload your stove with large pieces of firewood. A small, hot fire is the best type of fire for your flue.
  • Inspect your flue regularly. You can do this by going to your basement, opening the chimney cleanout door, and sticking a small mirror into the opening. Adjust the mirror so that you see the sky. You want to see a clean flue, along with the sharp, geometrical shape of your flue — usually round or rectangular — without any jagged edges revealing the existence of thick creosote. If your flue looks like it has a reduced diameter, it’s definitely time to clean your chimney.
  • Clean your flue and stovepipe regularly (at least once a year). If you plan to do your own chimney cleaning, you’ll need to buy a chimney brush that matches the size of your flue, along with some fiberglass extension poles that can be screwed together. You’ll need enough fiberglass poles to match the height of your flue. Cleaning a chimney is usually a two-person job. It’s best to have one person on the roof operating the brush, and one person in the basement shoveling out the creosote.

If you don’t feel confident enough to clean your own chimney, you’ll have to hire a chimney sweep to clean your chimney every year. The work is expensive but essential. Include the cost of annual chimney cleaning when you are trying to decide whether firewood is an inexpensive or expensive way to heat your house.

Locate your chimney near the center of the house. Ideally, the chimney will penetrate the roof at the ridge or very near the ridge. The farther the chimney is from the ridge, the more likely it is that wind turbulence associated with airflow over the ridge will cause the flue to downdraft. The top of the chimney should be at least 3 feet higher than the roofing at the chimney penetration, and should be at least 2 feet higher than the ridge.

What kind of stove should you buy?

To cut to the chase: I’m not going to tell you what brand of stove to buy. However, I’ll give you a few pointers.

Don’t try to heat your home with a traditional brick fireplace. Fireplaces are extremely inefficient; in many cases, if you light a wood fire in your fireplace, the net result is to cool rather than warm your house. (Fireplace chimneys encourage warm interior air to escape skyward; these air leaks rob more heat from your home than the burning wood supplies.)

You may be tempted to buy a pellet stove instead of a wood stove. If you like pellet stoves, go right ahead. But remember that virtually all pellet stoves require electricity to run, so they won’t work during a power outage.

Don’t be tempted to buy a used wood stove that was manufactured before 1990. Older stoves are much less efficient — in other words, they provide less heat per unit of firewood — than stoves that were manufactured in 1990 or later, after the Environmental Protection Agency (EPA) began requiring stove manufacturers to meet stricter efficiency requirements. Compared to a pre-1990 stove, an EPA-certified stove uses one-third less firewood for the same heat output.

EPA-certified stoves are also less polluting than pre-1990 stoves. The smoke emission limit for an EPA-certified stove is 7.5 grams of smoke per hour for non-catalytic stoves and 4.1 grams of smoke per hour for catalytic stoves. Pre-1990 stoves were much dirtier; they released between 15 and 30 grams of smoke per hour.

Buy a simple stove with as few bells and whistles as possible. A wood stove doesn’t need an electric fan. My favorite quote about electric fans on wood stoves comes from John Gulland, a writer for Gulland wrote, “A retailer friend of mine likes to tell customers who ask about efficiency boosts from fans that ‘you’ll get the same effect if you let me tape your $200 to the back of the stove.’”

Catalytic or non-catalytic?

There are two types of wood stoves: catalytic and non-catalytic stoves. I would advise anyone who is buying a new stove to choose a non-catalytic model, because catalytic stoves are fussy to operate. Catalytic stoves have another major disadvantage: their catalytic converters have a limited lifespan and are expensive to replace when they wear out.

A document on an EPA web site notes, “All catalytic stoves have a lever-operated catalyst bypass damper which is opened for starting and reloading. The catalytic honeycomb degrades over time and must be replaced, but its durability is largely in the hands of the stove user. The catalyst can last more than six seasons if the stove is used properly; but if the stove is over-fired, inappropriate fuel (like garbage and treated wood) is burned, and if regular cleaning and maintenance are not done, the catalyst may break down in as little as two years.”

Which brand of stove is most efficient?

There is only one thing to remember about wood stove efficiency: buy an EPA-certified stove. Beyond that, the efficiency depends more on the behavior of the person operating the stove than it does on the equipment.

Again, John Gulland provides good advice. Gulland explains, “All EPA-certified stoves run within the same band of overall efficiency (combustion and heat transfer) — about 70 percent plus or minus 10 percent. … The stove operator has a lot of control over the net efficiency it delivers. For example, wet firewood cuts net delivered efficiency … Also, firewood pieces that are too large don’t burn well at low firing rates and, again, demand large air settings that reduce heat transfer. When I buy a new wood stove (which is way more often than most normal people do), efficiency is not one of my criteria because I know they are all pretty much the same and that I’m the guy in control of net delivered efficiency.”

Buying firewood

Unless you plan to cut your own firewood, you’ll be negotiating with a firewood dealer. Firewood is sold by the cord. A cord is a volume of neatly stacked firewood measuring 128 cubic feet. The traditional way to stack a cord is to make the pile 8 feet long, 4 feet high, and 4 feet deep. If you are ordering 24-inch wood, such a cord is two stacks deep. If you are ordering 16-inch wood, such a cord is three stacks deep.

If you order a cord of wood, and the wood is delivered in an ordinary pickup truck, you’re being taken for a ride. A cord of wood won’t fit in a pickup truck bed. Moreover, a cord of seasoned hardwood weighs 3,700 pounds — more than twice the capacity of a 3/4-ton truck.

Before you order any firewood, ask what species are being offered. You want the densest available local species of firewood. Here in northern new England, that means sugar maple, beech, or yellow birch — definitely not white birch or poplar. Further south, hickory or oak may be available. In Alaska, your choice is probably limited to species that are considered junk elsewhere — species like spruce or aspen.

It’s not a good idea to burn green firewood. Firewood needs to be seasoned for at least one year; two years is better. To dry your firewood, stack it off the ground in a woodshed with a good roof. If you must stack it outdoors, keep it off the ground by stacking it on long poles or scrap pieces of lumber, and cover the top of your piles with old pieces of metal roofing weighted down by rocks.

If you want your wood to dry quickly, don’t restrict air flow through your wood pile. Don’t cover the pile with a tarp. If you are building a woodshed, you don’t necessarily need four walls. The smaller you split your firewood, the faster it will dry.

It’s hard to buy dry firewood. Almost any firewood dealer can claim that their firewood is dry, but it’s hard to verify whether the dealer is telling the truth. The best approach is to assume that you are buying green firewood, and season it yourself. By early September, I like to have two winters’ worth of firewood stacked and under cover. Half of the wood is between 12 and 18 months old, and will be burned soon. The rest of the wood is being seasoned for the following winter.

Be safe

If you are heating with wood, there are lots of ways you can burn down your house. Fortunately, the number of house fires caused by wood stoves and other heating appliances is on the decline. According to FEMA, the number of “heating fires” (defined as fires “caused by functioning or malfunctioning central heating units, fixed or portable local heating units, fireplaces, heating stoves, chimneys, and water heaters”) in the U.S. declined from 200,000 in 1983 to 49,000 in 2004.

A few safety tips:

  • Make sure that your stove is safely installed. It never hurts to call your local building department, fire department, or insurance agent to ask advice or to request an inspection if you have any doubts about the safety of your installation.
  • Keep flammable objects away from your stove, especially clothing, drapes, furniture, newspaper, and kindling.
  • Never put ashes in a cardboard box. Ashes should only be placed in a metal ash bucket. Once you have cleaned the ashes from your stove, the best thing to do with the ashes is to spread them above the snow that covers your vegetable garden. (Wood ashes contain potassium, a plant nutrient; ashes also help neutralize acidic soil. Never put wood ashes near blueberries, since blueberries prefer acidic soil.) If you can’t spread ashes in your garden immediately, place the ash bucket outdoors, away from the house, on a patch of bare ground, on a concrete slab, or in the snow — never on a wooden porch.
  • Don’t turn on your range hood fan while your wood stove is operating unless you’re sure that the exhaust fan won’t make your stove backdraft.
  • Before you go to bed, shut down the air intake dampers on your wood stove to a low setting.

Can you put a wood stove in a Passivhaus?

Passivhaus buildings are very tight — so tight that wood stoves may not operate well. There are two potential problems: in a very tight house, a wood stove might be starved for combustion air; and the heat output of a wood stove might be more than a superinsulated house requires.

Opinions differ on whether it’s possible to install a wood stove in a Passivhaus. At least two European stove manufacturers advertise wood stoves that are touted as appropriate for Passivhaus buildings:

  • Rika, an Austrian stove manufacturer, sells the Vitra Passive House Stove. The stove uses ducted outdoor combustion air.
  • Normatherm-Stahlheizkesselbau GmbH, a German stove manufacturer, sells a $7,100 stove called the Atago Design NK 20 (also known as the Normatherm KKH 20) that is said to be appropriate for a Passivhaus.

According to Mark Sidall, a Passivhaus consultant and designer in Newcastle Upon Tyne, England, Dr. Wolfang Feist advises against the installation of a wood stove in a Passivhaus. Sidall explained that in 2005, Feist wrote a technical paper on the topic: “Feist reported that there were no suitable wood burners for Passivhaus projects.”

A Swedish document (“Passive Houses in Sweden”) answers the question with a “maybe”: “Standard solutions for the integration of wood stoves into passive houses do not yet exist and need to be carefully planned in each project. Heat radiated and convected from the stove can quickly exceed the heating demand of the room where it is located, causing overheating. The heating power in the stove needs to be low (i.e. 1 – 3 kW) so as not to cause too high indoor temperatures. Only a few stoves with this required low heating power are available on the market. If a wood stove is desired, it is important to balance the ventilation system correctly to avoid the case of an underpressure in the room drawing out flue gases. The wood stove must have a separate air supply and the heat should be extracted from the stove via a heat exchanger. The heat can be used for heating other rooms or for heating domestic hot water.”

A British web site answers the question in the affirmative: “You can install a very small wood burner in a Passivhaus; however, using it in all but the coldest winter days could risk overheating unless one was very careful about how much wood was added.”

I know of at least five Passivhaus residences that include a wood stove:

  • A Passivhaus built in Reims, France, in 2007 is equipped with “a very efficient wood stove.”
  • Glenn Haupt, a certified Passive House Consultant in Bend, Oregon, installed a wood stove in a Passivhaus in Walla Walla, Washington. Haupt wrote, “I used a simple, small Vermont Castings wood stove 7,000 BTU min output ($800 retail) … They burn a few scraps of wood on a cold morning and it carries them through to the next morning, most of the time. … Combustion air is coming directly into the box from outside, no smoke or drafting issues.”
  • The primary heat source for a Passivhaus in Lancaster, New Hampshire (built by Garland Mill Timberframes) includes an “EPA-certified wood stove with dedicated combustion oxygen.”
  • The heating system for a Passivhaus in Shelburne, Vermont (designed by Carol Stenberg and built by Tom Moore) is described this way: “The house has a wood stove as well as solar hot water panels and resistance electrical hot water for heating.”
  • The space heat for a Passivhaus in Nova Scotia (the Solterre Concept Cottage) is “supplied by solar energy, both passive and active, and a small, high-efficiency wood fireplace.”

Rachel Wagner, an architect at Wagner Zaun Architecture in Duluth, Minnesota, has designed several tight superinsulated homes that include wood stoves. One of these homes (the home of Gail Olson and Erik Peterson in Esko, Minnesota) includes a Hearthstone Tribute wood stove. “I have had no difficulties putting a wood stove in such a tight house,” said Wagner. “I’ve done it more than half a dozen times, all in houses testing at less than 1 ach50. In the houses that also have a range hood, we caution the homeowner to pay attention before turning on the fan. Two homeowners report having to sometimes crack a window when the wood stove is used at the same time as an exhaust appliance like the range hood or the clothes dryer. We’ve provided dedicated combustion air routes in a couple of the houses, but not all.”

Another example of a Wagner Zaun house with a wood stove is a Duluth home that tested out at 0.7 ach50. The home includes an EPA-certified wood stove with ducted outdoor combustion air.

In spite of these examples of (apparently) successful wood stove installations in Passivhaus buildings, a few builders have reported problems. Jesper Kruse, a Passivhaus consultant in Greenwood, Maine, helped design a Passivhaus building for Ken Hotopp and Robin Gorrell in Newry, Maine. Kruse reported, “The house was designed to be heated by a small wood stove. We chose the Morso 3142 stove, since its heat output is a close match to the design heat load, and since the stove has a ducted outdoor air kit. We ran the outdoor air duct under the slab. When it came time to hook up the stove, however, we learned that experts have mixed thoughts on ducted outdoor air for wood stoves. We decided to hook up the stove without the ducted outdoor air supply and see what happened. (First, though, we had a discussion with the owners on the importance of being extremely vigilant while the stove was burning, to watch for back-puffing). … They had to crack a window to get the fire going, there was the smell of smoke at one point. I think the fact that their firewood wasn’t fully seasoned made the problem worse, but regardless of the cause, the stove just wasn’t working right. So we decided to hook up the air supply. It turned that the duct is not directly connected to the firebox; it’s just kind of close. … Although the wood stove is not a success so far, the owners really like the idea of being able to heat the house when there is no power, and so we’ll keep working on it.”

Another example of a Passivhaus project that encountered wood stove problems is the Jung Haus in Oakland County, Michigan. According to an author who identifies himself as G. Kragler, “The Jung Haus is … designed and certified to the German ‘passive house’ standard … The Jungs had originally insisted on a small wood stove in the first floor living room. After much deliberation, it was eliminated since we could not figure out a way to meet the air tightness and thermal insulation standards required for Passive House certification with a leaky stove damper.”

Wood heat resources

Here are links to two valuable online resources for anyone seeking more information on heating with wood:

Martin Holladay’s previous blog: “Weatherization Funding Has Been Slashed.”

Click here to follow Martin Holladay on Twitter.


  1. Eric Peterson | | #1

    Any experience with Masonry heaters?
    I am considering installing a small modular masonry heater/ bake oven in the home I am planning, probably one from Eco-firebox in Maine. ( It seems like way they work would be better for a super tight building than a traditional woodstove. A small hot fire in a huge pile of masonry that very slowly releases its heat for hours after the burn. I know they are not cheap, it's definitely an aesthetic thing, but I was also thinking that all that masonry will function as thermal mass from a passive solar perspective as well, as long as I place it in direct sunlight. Are you aware of any use of these in high efficiency homes?

  2. User avater GBA Editor
    Martin Holladay | | #2

    Response to Eric Peterson
    Some of the issues surrounding your question were discussed in a GBA article, Are Masonry Heaters a Good Match for Superinsulated Houses?

    Here are my comments: a masonry heater is a good way to heat a leaky, poorly insulated building. Masonry heaters have at least three big drawbacks: They cost an arm and a leg. They take up a lot of room. And during cold weather, they require the homeowner to kindle a fire from scratch twice a day.

    There is a standard piece of advice that I give to anyone who is contemplating the purchase of any expensive heating equipment: why not take the money that you would have spent on the expensive masonry heater, and spend it instead on air sealing details, better insulation, and better windows?

    If you improve your thermal envelope, you won't need such a big heating system.

  3. Skip Harris | | #3

    You may still be able to
    You may still be able to leave for the weekend if the house temp won't drop too low with no fire. Perhaps it is built well enough that the plumbing will not drop below freezing, ever, and the stove is used for comfort rather than freeze prevention.

    I would like to emphasize the importance of hot fires. I used to clean my chimney yearly, but after the first few years learned that starting a fire fast and hot, using nice dry wood, and never restricting air before only coals remain leaves me with a pristine chimney. I still check it though...

    I agree, though: it is better to build well and not to need to burn the stuff at all, for lots of reasons.

  4. Eric Peterson | | #4

    I like masonry..
    Thanks for the reminder about that article. It's worth re-reading.

    I'm aware of the cost and I wouldn't be exchanging a good envelope for a masonry heater. I'm a carpenter by trade and a half decent mason, so I could and in fact want to, do a lot of the finishing myself. One of the alternatives that is mentioned a couple of times in that article, the Vermont Bun Baker, approaches $7k if you go for the version with the most soapstone, so that's hardly a budget choice either.
    I took Marc Rosenbaum's net zero class this spring and he mentioned that he would be using both a wood stove and mini-splits in his next project, with the idea that the mini-splits operate less efficiently at really cold temps, and the woodstove is a hassle during the shoulder seasons, so the two systems would complement each other well.

    Like I said, a big part of this is the aesthetic and the desire to do the work. I am prepared to accept that I may be bull-headedly pursuing an irrational and purely aesthetic goal, but I am curious if anyone else has done a similar thing and what their experience was.

  5. User avater GBA Editor
    Martin Holladay | | #5

    Response to Dustin Harris
    If you are lucky enough to live in a very tight, superinsulated house -- or a mild climate -- you're quite right about leaving the house unheated for a few days, even in January.

    Alas, my house doesn't fall into that category. If I leave the house in January, when the temperature can drop to -30°F, my house is neither tight enough nor well enough insulated to keep my pipes from freezing. So I have to light a propane space heater when I leave in the winter.

    You're also correct that hot fires and much better than smoldering fires. Hot fires keep your flue clean -- just as a vegetarian diet keeps your arteries clean. It's still a good idea to inspect your flue annually, however.

  6. Lucas Durand - 7A | | #6

    Though I don't consider myself an expert on this subject, I do have some experience and I found your article to be very comprehensive.

    A couple of minor things I thought of while reading:
    Old pallets make a great surface to stack your firewood on.

    Where I live, a person will save the most money by buying cordwood in 8' logs.
    Last year, birch (the best common firewood in this area) in 8' logs went for $100/cord and when split went for $300/cord.

    When shopping for firewood, try to buy from someone who hasn't skidded the logs through a swamp or mucky clay - firewood that is excessively caked in dirt and mud sucks.

  7. User avater GBA Editor
    Martin Holladay | | #7

    Response to Lucas Durand
    I haven't heard of 8-foot firewood logs. Here, the people who want to save money buy "tree-length" logs right off the logging truck. The logging truck comes straight from the woods to your dooryard.

    Muddy logs will dull your chainsaw quickly. So buy your tree-length logs in mid-winter, when the logs have been skidded on snow.

  8. User avater GBA Editor
    Martin Holladay | | #8

    Response to Kevin
    At least once a year, it seems, there is an article in a local Vermont newspaper about a rental house fire. The newspaper stories usually include this sentence or one very much like it: "Fire investigators determined that the fire started when the tenants removed ashes from the wood stove, put the ashes in a cardboard box, and placed the box on the porch."

  9. Kevin Dickson, MSME | | #9

    Bad Experience in Montezuma, CO
    Woodstoves are ubiquitous in the mountains of Colorado. One particular landlord in the area has had three homes burn down because his renters were ignorant of the maintenance and safety issues in regard to wood stoves.

  10. Malcolm Taylor | | #10

    Excellent Advice
    Great blog as usual. One regional difference out here in the PNW: Firewood suppliers don't worry about the load capacity of their pickup trucks. They wedge a small log into the leaf springs and hope for the best. I know as I follow them from the cut blocks around me hoping they make it to their clients in one piece while spilling rounds on the way.

  11. Dick Russell | | #11

    My house is superinsulated
    My house is superinsulated and very tight (last blower door test gave 0.8 ACH/50). It has a small woodstove on the lower level, with a firing range of 11-28,000 BTU/hr, according to the tag that was on it. The heat loss model for the house showed a design heat loss of 22,000 BTU/hr. The house is big enough that for the 4-6 hours we sometimes use the stove, starting around supper time, we don't get what you'd call overheating. The house seems to absorb the heat easily for that duration.

    I like to burn a medium sized but hot fire, with no noticeable smoke from the chimney. The stove has a ducted outside air source connected directly to the back of the stove. I have to be careful when lighting off the fire, making sure that neither the clothes dryer nor range hood is operating then, or I get downdrafting, with smoke leakage past the stove door gasket. Once the stove is burning well and drawing smoothly from the outside air duct, the clothes dryer or range hood can be used. However, using the range hood on the highest setting without opening a window nearby can be problematic.

  12. Greg Smith | | #12

    burning soft wood

    Thank you, great read as always.

    However on one point I am going to disagree and that is on burning soft woods and resins and creosote build up. That one is a very (very) common myth.

    Creosote build up is a moisture issue - burn wet wood or burn cold and you get creosote build up - burn dry wood and burn hot and you don't get creosote build up - apples to apples comparison between hard woods and soft and there is little to no difference between one or the other pertaining to creosote build up.

    Keeping in mind the other points that you mentioned such as warm chimney, etc. which potentially do have a significant effect on creosote build up - much more so than wood choice.

  13. Jason Crawford | | #13

    But why?
    Hi All,
    I've read many times that fire places draw heat from the house, but I've never gotten an explanation for WHY that's more true for a fire place than a wood stove. Certainly the same forces must be at play. What's the difference? Is it absolute or is it also a matter of how one adjusts something?

  14. Dick Russell | | #14

    Fireplace vs woodstove
    While a fireplace may heat the area immediately around it, by radiation, an open hearth and wide open flue draw a huge amount of excess room air and send it up the chimney. That air must come in through the myriad leakage points throughout the house, making chilling the rooms away from where the fireplace is located. Further, if the thermostat for the heating system is in the vicinity of the fireplace, the thermostat may remain satisfied while the rest of the house is much too cool for comfort.

    A woodstove, with its door latched, draws just enough air for efficient combustion. For a small woodstove, this may be only 40-50 cfm, well within the potential leakage rate of even a very tight house. That's why a woodstove actually can work in a tight house without an outside air source. Still, I would advocate having the outside air duct, to nearly eliminate draw of inside air up the chimney at times when the stove is not in use, and particularly when the fire has burned out for the night. Of course, if the firebox is loaded for an overnight burn, this is not an issue.

  15. User avater GBA Editor
    Martin Holladay | | #15

    Response to Greg Smith
    Thanks for your comment. I am always willing to learn and acknowledge my mistakes. Do you have any references to published documents backing up your statement about softwood fuel and creosote?

  16. User avater GBA Editor
    Martin Holladay | | #16

    Response to Jason Crawford (Comment #13)
    Dick Russell's explanation is correct. Here's another factor: while a fireplace fire heats nearby objects and people by radiation, the fire mostly heats air that is in the fireplace -- air that is on its way up the flue. A stove fire, on the other hand, heats the steel or cast iron which surrounds it -- and that steel or cast iron is located in the room, not in a flue. So the hot steel helps heat the house.

  17. Greg Smith | | #17

    Martin,I suspect that there

    I suspect that there has to be some sort of definitive document hidden somewhere in cyber-land, but if there is, I couldn't find it.

    I did find a fair bit of anecdotal information on various chat sites and a few articles addressing the issue. Nothing conclusive from a recognized authority though.

    This is about the best I could find:

  18. User avater GBA Editor
    Martin Holladay | | #18

    Response to Greg Smith
    Thanks for those links. I appreciate the information, and I have edited my article.

  19. George S | | #19

    why I do it
    I’ve been heating with wood since 1984, so I fall into the class of people who “ may even have figured out how to install and operate your stove safely.” I agree with you cutting and splitting wood is time consuming, and I realized early on that if I wanted to heat with wood, I’d have to buy it cut and split, which I do ( I work for a living and had to compromise)

    My house meets two of the qualities listed for homes where wood heat makes sense
    • Compact two-story homes rather than stretched-out single-story homes;
    • Homes with an open floor plan rather than homes with many small rooms and many closed doors.
    The reason why I first used wood, besides early poverty of the ex grad student, was that the electric in my area was not reliable. It was necessary to have a source of heat that would last through the mid winter storms. This is now not as big a problem as it used to be.

    I recently upgraded to a wood stock progress hybrid soapstone stove, a beautiful device to look at as well as to use(1). It’s hybrid because it uses both a catalytic device, and secondary heated air combustion. The particulate emission rate is 1.33 gm /hr (2). Measured efficiency is 81%. The progress hybrid even has an outside air intake, for sealed combustion use in a motor home, though in my opinion, you’d need a pretty big motor home. The biggest quality is that a soapstone stove heats up slowly, and releases the heat over several hours compared to a cast iron or steel stove (which heat up quickly and go cold quickly). Hearthstone site has a good graphic on this quality(3).

    For the weekend problem , when I’m not there to stoke it, I now use a Fujitsu RLS2 split duct heat pump, before the heat pump I used a propane wall heater back up. FWIIW, I have solar panels on the roof and am a net energy generator, which I intend to someday burn up in the heat pump, but not just yet because I like wood heat. I use microinverter grid tied solar panels because there are no moving parts. The SREC credits more than pay for the wood

    As to Martin’s question ” why not take the money that you would have spent on the expensive masonry heater, and spend it instead on air sealing details, better insulation, and better windows?” my answer is that because it is boring and dull. That , and I really do not want to tear apart my house, I want to live in it. I want to live in a house full of light and heat and fresh air. Sometimes I leave the windows open in dead of January so that I toast myself on the wood stove side, and cool on the window side. It’s fun, even though das ist verbotten to the air leak fearing heat calorie counting passiv haus aesthetes.

    There is an aesthetic element, present company excluded, that the passive haus devotees seems to miss. At the limit, it seems this crowd, again present company excluded, want folks to live in a windowless foam box, with a double sealed air lock suitable for immersion to 30 m depth, with only a heat exchanging snorkel to allow fresh air to enter, preferably heated with the glow of a 2 watt led bulb

    A wood stove is a thing of beauty, and the winter rhythms of tending to it are a joy.

    That’s why I do it

    (2) (3)

  20. Tyler Forbes | | #20

    Fireplace Boiler Combos
    There are three factors that are required to achieve successful fire in a low ACH house.
    -A sealed OAK (outdoor air kit) to the manifold, and by sealed not a just a duct to the general area
    -Keeping the dryer and range vent off when the door is open to prevent backdraft
    -Minimizing wood stove fire output. Unfortunately the days of McMansions has lead to a lot of the attractive units with outputs of 40-80k btu, which is way to much output. There are number of new companies integrating water jackets above fireboxes which will allow for a 30%/70% split storing additional thermal energy in water for use in hydro air setups or DHW.

  21. Greg Smith | | #21

    Response to Martin Holladay
    You are more than welcome.

  22. Mark Klein | | #22

    Masonry Heaters and softwood
    I agree with Martin that good design, air sealing and insulation trump expensive heating systems. Masonry Heaters are expensive compared to a nice EPA certified Phase 2 Parlor stove. Generally speaking fuel efficiency and emissions are somewhat better for Masonry Heaters but not enough to justify the added cost. Masonry Heaters do have some qualities which distinguish them from steel or iron parlor stoves. They allow high temperature combustion fires (including softwood) without causing overheating of the house because the structure of a Masonry Heater is a thermal battery with relatively low output radiant panels, typical heater output is around 20,000 BTUs an Hour. This actually is a reasonable output for an efficient home many freestanding stoves are rated at 40-60,000 BTUs an hour which can cause homeowners to choose a strategy of small restricted burns in an effort to avoid overheating. This can lead to high emissions, and creosote condensing in the chimney. The footprint of a masonry heater is actually pretty similar to the footprint of many other wood burning devices if the clearance to combustibles required for steel or iron stoves is accounted for. Finally if a homeowner is willing to pay for a classic masonry hearth Masonry Heaters allow that with performance as good or better then almost any other cordwood (or pellet) burning device.

  23. George S | | #23

    masonry heater emission and efficiency
    I was curious about the emission rates of masonry heaters. Particulate emissions for Masonry heaters are listed in gm/kg, and wood stoves in gm/hr
    Turns out, it’s hard to compare because they operate differently:

    “Moreover, the very different operating profiles for masonry heaters compared to woodstoves present difficult issues when attempting to make "equivalency" findings. The fuel load in a masonry heater is fully-consumed in a short period of time. This heats a large mass of refractory, which in turn discharges the stored heat over many hours. Woodstoves are also batch loaded, but the heat is delivered as the fuel load is consumed. The length of the burn depends on how the operator sets the air controls. When comparing emissions performance on a gram/hr basis, the masonry heater emissions must be averaged over the period of time that useful heat is being provided to the home in order to compare them with woodstoves on an "apples to apples" basis.

    Fig 4 on p 18 of this document comes closest to a comparison.. the grundofen beats out the phase 2 epa wood stove on a gm/hr basis

    The other issue is efficiency : masonry heaters are in the 60% category, and best EPA wood stoves in the 80% range.. this is reasonably important if you are hauling wood

    But.. the best way to improve the system efficiency is to lower the heat loss through the walls.. which I believe is Martin’s main point

  24. Malcolm Taylor | | #24

    Another consideration for those living in the PNW or other active seismic zones when choosing to install either a masonry heater or chimney is their performance in an earthquake. I have seen a Finnish heater reduced to a pile of soapstone by rock blasting on a neighbour's lot.

  25. User avater
    Dana Dorsett | | #25

    Combustion air volumes (reponse to Dick Russell, in post #14)
    Dick Russell writes:

    "For a small woodstove, this may be only 40-50 cfm, well within the potential leakage rate of even a very tight house."

    Combustion air flows of 40-50cfm not a small wood stove, that's a MONSTER woodstove (or a small open hearth fireplace.) At the small end the max combustion air flow rates for a sub-30,000BTU/hr stove will be ~10cfm, and throttled back it'll be 3-5cfm. A 150,000BTU/hr behemoth might draw as much as 25cfm or even a bit more at max-fire, but not more than 10-15cfm average.

    But the basic point is correct- an open hearth fireplace pulls orders of magnitude more infiltration air than a wood stove, and even a fairly tight house has enough air leakage to supply combustion air for small woodstoves, as long as there isn't active exhaust venting in progress. A house that tests at a fairly low 500cfm/50 has the leakage equivalent of a 3.5" diameter hole in the wall, which is bigger than the dedicated combustion air duct for a substantial sized woodstove, but smaller than a clothes dryer duct.

    And the rationale behind dedicated combustion air piped directly to the woodstove is the backdrafting potential under active exhaust venting in tight houses. A combustion air duct that only comes NEAR the woodstove rather than directly hooked up to it in a nearly air-tight manner needs to be able to handle more than just the 10-25cfm the wood stove needs, but also the homes combined exhaust venting volume to reliably achieve that end. Even then, wind pressures can sometimes reverse the flow in the flue, but as long as the combustion air is ducted directly to the woodstove and not the house, the flue gas (and potential embers) go out the combustion air duct rather than into the house. (Combustion air ducts need clearances to combustibles for exactly this reason.) It's difficult to make the wood stove, combustion air duct, & flue all completely air-tight, but in tighter homes it's definitely worth given it some attention when installing wood burning stoves.

  26. Don Fugler | | #26

    Outdoor air supplies and woodstoves

    CMHC undertook several studies on woodstoves and spillage. They are probably archived now but I can dig them up if you want the specifics. What we do know is this:
    - Outdoor air supplies will reduce the amount of indoor air used by the woodstove (but they may affect the woodstove efficiency in cold weather - I do not have data on this tradeoff)
    - The ducting for outdoor air supplies must be designed to tolerate backdrafting, because they likely will. Think of your outdoor air supply as a horizontal flue pipe in terms of clearance to combustibles.
    - Your woodstove will rarely if ever backdraft or spill during the main burn. At that time the chimney is developing so much draft, or woodstove depressurization, that it is far beyond whatever depressurization you create in your house. We have measured up to 50 Pa of draft. At the fire die-down stage (often in the middle of the night), there is little heat left to create draft but there is still good CO production. Spillage is possible then. Protect yourself with CO and smoke alarms.
    - An outdoor air supply does not eliminate spillage. The pressures in the house and stove can still create a positive pressure to the house. We have measured this. When spillage happens, the relative tightness of the door closure or air openings are what will determine how much spills into the house. In an open fireplace, this could be all the combustion gases. In a tight woodstove, or a fireplace with tight doors, the spillage will be reduced but not eliminated.
    - In tight houses with relatively neutral pressures (e.g. no large exhaust appliances), a small woodstove should be able to operate fine without an outdoor air supply.

    I agree that the website is full of good information. Many of the research projects CMHC undertook had John Gulland as a contractor or advisor.


  27. Stephen Martinson | | #27

    One other thing to consider when selecting a wood stove is what your insurance company will allow.

  28. Josh Wimpey | | #28

    Firewood seasoning --- a couple of points
    1) Drying takes place almost exclusively through the end-grain so splitting logs does not make them dry faster
    2) Moisture content is close to minimized after only 4 months. No need to season for 1 to 2 years

    There are a couple of very good and very technical papers on the subject but it is worth noting that the information posted in this blog may be misleading.

  29. User avater GBA Editor
    Martin Holladay | | #29

    Reply to Josh Wimpey
    The speed that firewood dries is highly dependent on your climate. While green firewood may dry in 4 months in Arizona, it certainly won't in the rainier parts of Oregon, Alaska, or Vermont.

    There's also the question of "which 4 months?" You'll see more drying during June through September than December through March.

  30. Charles CAMPBELL | | #30

    Martin, thanks for a very
    Martin, thanks for a very timely article. I've been researching woodstoves for a few weeks, hoping to buy one soon. In addition to the lists at and , you might want to share with readers the attached sortable spreadsheet my brother got from Larry Brockman at EPA.

    2 questions:

    1. Under what circumstances would you choose triple wall rather than double wall chimney pipe?

    2. Are there any stove brands that are considered the "Honda" or "Toyota" of stoves? That is, high value brands that combine quality (efficiency, reliability and durability) with low prices?

  31. User avater
    Dana Dorsett | | #31

    In a solar wood kiln...
    ... it doesn't much matter- any four months will do, as long as you're far enough south of the arctic circle.

    Stacked in the field and buried in the snow from December-March is a bit less optimal... ;-)

    Even stacked in an open shed (still out of the rain) there's no way freshly cut green wood becomes wood-stove-ready in any four months in New England. Cut down dead trees or deadfall, maybe. Drying rates are a function of the wood temperature, and the relative humidity & air velocity of the proximate air. A reasonably designed passive-solar wood kiln improves all three.

    Species also matters. (Cottonwood, anyone? :-) )

  32. User avater GBA Editor
    Martin Holladay | | #32

    Another reply to Josh Wimpey
    I also disagree with you claim that "splitting logs does not make them dry faster." Try this experiment: cut down a 16-inch-diameter yellow birch tree. Cut two 24-inch-long pieces of firewood from the trunk. Split one chunk of yellow birch into 16 pieces, and leave the other one unsplit, with its tight green bark. After three months of drying, tell me whether your 16-inch-diameter round piece is as dry as my 16-inch split pieces.

  33. Charles CAMPBELL | | #33

    George wrote, "The other
    George wrote, "The other issue is efficiency : masonry heaters are in the 60% category, and best EPA wood stoves in the 80% range.. this is reasonably important if you are hauling wood." I'm told that evaluating both masonry heater and stove efficiency is a slippery subject. Where are you getting these numbers, and why do you trust them?

  34. Eric Peterson | | #34

    Masonry Heater efficiency...
    Masonry heater manufactures and advocates claim 80% as well, I've not seen the 60% number before.

  35. Charles CAMPBELL | | #35

    Martin wrote, "Never put wood ashes near blueberries, since blueberries prefer acidic soil." Here in Georgia that advice also applies to azaleas and sometimes hydrangeas.

  36. Brian Godfrey | | #36

    One thing I can agree with is
    One thing I can agree with is the assertion that city people probably shouldn't own wood stoves. All this malarkey about inconvenience and having to cut the fuel and so on is about what I'd expect from them. They are about as clueless about such things as I am about why anyone would live amongst so many people that you can smell them as you come into town.

    But an old fashioned wood stove isn't what a self-described "energy nerd" should be wasting his time on, anyway. Why not do an actual, real-life evaluation of a rocket stove? Those fascinate me and I'm thinking of building one into an attached "porch" and circulating that heat into my house through some probably non-approved through-wall vents - one high and one low to allow gravity to do the work for me.

  37. User avater GBA Editor
    Martin Holladay | | #37

    Response to Brian Godfrey
    Once you've built your contraption and lived with it for a few months, please write a blog about your experience. We'll publish it.

  38. User avater
    Dana Dorsett | | #38

    I live in the city...
    ... I own a woodstove, and operate it regularly.

    Worcester MA is a veritable urban forest. One of my neighbors makes his living as an urban logger, dealing with all sorts of removal & tree maintenance issues. "Free" wood abounds for those with the means of picking it up, and wood dealers are happy to deliver. At least 3 homes on my block are heated at least partly with wood, and friend across town hasn't run his gas-fired steam boiler in the dozen odd years he has lived there, heating his 2-1/2 story + basement antique exclusively with an airtight wood burning insert.

    It takes bit of yard (or a ventilated garage/woodshed) for storage space to heat with wood, and some neighborhoods are too dense for that. But the notion that it's not a viable option for urban dwellers is bunk- it depends on the urb and the nature of the 'hood. But it's clearly not for everyone (rural or urban).

  39. User avater GBA Editor
    Martin Holladay | | #39

    Response to Dana Dorsett
    Urban residents who want to heat with wood have to consider at least three issues. You have addressed two of them: fuel availability and firewood storage.

    The third issue -- the one you didn't address -- is a question of etiquette or ethics: does wood burning in an urban area unfairly burden neighbors who have to breathe the particulates emitted by the wood stove? There is no clear answer to the question, but the question must not be ignored. For more on the issue, see Should Green Homes Burn Wood?

  40. Yuri Kinakin | | #40

    Outdoor Wood Burning Stove
    Hi Martin,

    Thanks very much for your interesting post. I've been planning the construction of an airtight home and have spent time considering this topic. One solution that had been proposed to me was going the outdoor boiler route (place in a detached garage), with hot water being plumbed into the house. While I agree that typical wood boilers are generally quite nasty, do you have any opinions to offer on the newer, gasification units? For example, the Empyre Elite XT is rated to burn at 0.071g carbon/MJ. Thanks very much,

  41. User avater GBA Editor
    Martin Holladay | | #41

    Response to Yuri Kinakin
    For those who insist on installing an outdoor wood-fired boiler, it's important to choose a model that has received the EPA "white tag" certification. It looks like the Empyre Elite has a white tag, so that's good.

    I have no experience or knowledge of this boiler, so I can't tell you whether it's sensible to buy one. It costs at least $7,000 plus installation, many times the price of a good wood stove. It requires a lot of electricity to run. I still think it makes sense to spend less on your heating equipment, and more on your thermal envelope. If it costs you $10,000 for your boiler (once it is installed), you might consider instead buying a $2,000 or $3,000 wood stove, and spending the extra $7,000 or $8,000 on more insulation or better windows.

    Finally, a fairly high number of purchasers of outdoor wood-fired boilers have complained that many models don't last very long. I have heard reports of rust and leakage. It doesn't take many problems with these boilers before the unit has to be scrapped, and it's time to buy a new one. That's expensive.

  42. Yuri Kinakin | | #42

    Response to Martin Holladay
    Hi Martin,

    Thanks for the considered response. One quick point is that placing it in a garage should reduce some of the wear and tear on the unit.

    The idea of getting a regular wood stove and spending the difference on improved windows is well taken. Our idea with the house is that we're willing to pay a higher up-front cost for a house that will have a low cost to operate. Running an extra water pump for this unit is probably much more expensive that getting a good water heater, a decent wood stove and some high efficiency windows. Thanks for the reality check.

  43. Tom Bator | | #43

    Great article!
    You forgot to list one more challenge posed by wood stoves: SNAKES! I have to store my wood in the back yard, and every once in a while, a copperhead snake decides my nice, dry wood is a great place to spend some cold fall evening. That said, it is still worth the risk to me.
    People don’t really consider the efficiency and practicality of wood burning stoves anymore. Obviously the E.P.A cares nothing about how much coal is NOT burned when people use wood stoves efficiently. The reality is that they are quite efficient and when really used properly quite enough to heat many areas.

  44. John F Cross | | #44

    Masonry Chimneys - Supaflu
    I have had good experience with 3 Supaflu liners, since the '80's. One, on a 1920's built, 2 story, lined with (broken) clay tile. Ceramic wall tiles in my bathroom were 'pushed' askew, when the liner was installed - indicating how bad the existing chimney was.
    The other two, were in a new construction, one was 2-story, the other, 1-story - lining the brick 'hole'. Two years ago, the 'above the roof' part was repaired - new brick, and a liner made with 1/3 Poraver as aggregate in the mix. Supaflu was not used because of the expense, for a small job, in a water access location. I am very pleased. The liner is quite solid (knocking it down) and has a R value (insulation).
    I am surprised that I don't see many references to Supaflu. I did not want a metal chimney, that I thought would have to be replaced (by my successors).

  45. User avater GBA Editor
    Martin Holladay | | #45

    Response to John Cross
    Thanks for sharing your experiences with Supaflu.

    For GBA readers who are unfamiliar with the Supaflu system, it is a cast-in-place chimney lining product used to repair existing masonry chimneys.

  46. Ruth Von Goeler | | #46

    Stove air sealing metrics and pressure warning device
    Thanks for the comprehensive article. I have read that in an airtight house in addition to combustion air, it's important to have a an air tight stove. I've never seen these statistics published. Is there a good metric for the airtightness of the fire box? Are there brands of stove you can recommend that have better air sealing.

    Also,in a very air tight (less than 1 ACH50) house that we built, we installed a small wood stove (with dedicated combustion). The house also has a range hood fan (max 350 cfm at high speed) with a dedicated make up air vent. The owners have periodically smelled smoke (presumably from backdrafting) and we want to find a pressure warning device that could alert the owner when the house is depressurized. Can you recommend one for this purpose?

  47. Trent Hardy | | #47

    Question about installing ducting
    I have a woodstove installed in the basement of my home with a brick chimney that is located outside of the house. This is doubtlessly not a very efficient set up, and I have been looking for ways to improve the heating ability of this stove. However, both the chimney and the roof of our house is quite new (<5 years), and financially it doesn't make sense for us to install a new chimney up through the first floor. in addition,our space requirments don't really allow relocation of stove that level.
    Recently I have attempted to increase the heating efficiency by surrounding the woodstove with a "box" of metal sheeting, then tying some ducting into this box which then leads to the first floor of the house. I have had some pretty good success with this. Without use of any type of fan, abundant heat empties out of the ducting, and it seems to have helped "balance" the temperatures between the two levels. For example all winter, to get the heat to 22oC on the first floor, it would pretty much be 34oC in the basement, while now the ratio is more like 22oC : 25oC
    However, I am a little concerned that there may be safety issues or building code violations inherent in to this method. I have tried searching for information on the web, but have so far been unsuccessful. Has anyone heard of this method/any issues with using it? Any info would be much appreciated.

  48. User avater GBA Editor
    Martin Holladay | | #48

    Response to Trent Hardy
    Indeed, your modifications of your wood stove undoubtedly violate the stove manufacturer's recommendations and may pose a fire safety hazard.

    What you are trying to do, evidently, is build a home-made wood furnace. Here's my advice: if you want a wood furnace, buy a wood furnace. (A wood furnace is designed to be hooked up to ductwork.)

  49. Trent Hardy | | #49

    Sounds good. Thanks very
    Sounds good. Thanks very much for the advice :-)

  50. Bill Daugherty | | #50

    Burning soft wood
    We burn Southern Pine. As long as the wood is properly dried, and a stovepipe thermostat is used to keep the stove operating in a proper heat range, I've found that burning pine creates very little creosote buildup.

    A masonry chimney on an exterior wall will always produce much more creosote than an insulated metal chimney, especially an interior insulated metal chimney.


  51. Bill Daugherty | | #51

    Links on burning pine
    I've attached some links below on the topic of burning pine and other softwoods below.

    When you read through the info below, you'll notice that the importance of burning dry wood is stressed a number of times. Also, there are a number of mentions of burning the pine during the day, and using the hardwoods for an overnight burn.



    Burning pine wood ? | Forums Home

    This question has been beat to death here ,but it keeps popping up. Pine is fine as long as its dry period. Any wood burned wet or green will cause trouble. I burn mostly pine in 3 different brands of EPA non cat stoves,cuz i have so much of it. Only difference is you have to load the stove a little more often.


    Southern Yellow Pine easily burns at varying heat levels and is easy to split. It emits some smoke and sparks but makes a relatively good firewood.

    Read more:


    Back in the early 1980's, tests were conducted to discover which kind of wood created the most creosote in a regular "open" fireplace. The results were surprising. Contrary to popular opinion, the hardwood's, like oak and madrone, created MORE creosote than the softwoods, like fir and pine. The reason for this, is that if the softwoods are dry, they create a hotter, more intense fire. The draft created by the hotter fire moves the air up the chimney faster! Because it is moving faster, the flue gas does not have as much time to condense as creosote inside the chimney. Also, because the flue gas is hotter: it does not cool down to the condensation point as quickly. On the contrary, the dense hardwood's tend to smolder more, so their flue gas temperature is cooler. Thus, more creosote is able to condense on the surface of the flue. So, saying that "fir builds up more creosote than oak" just isn't true! It is a misunderstanding to think that it's the pitch in wood which causes creosote. It's not the pitch that is the problem, it's the water IN the pitch. Once the water in the wood has evaporated, that pitch becomes high octane fuel! When dry, softwoods burn extremely hot!

    Which kind of wood is better? That depends on what you want. If you are a first time fire-burner, or if you only want to burn a couple dozen fires a year: definitely go with a DRY softwood, like fir. Your odds for being happy are infinitely higher with fir, especially if you are just now buying wood for this year. The fresh aroma of fir creates a lovely holiday ambiance! Fir seasons quickly, and when it is dry it is truly delightful, trouble free wood! It's easy to get going. It smells great. It's easy to split for kindling. It creates BIG, friendly, luxurious fires! But, it doesn't last as long as oak or madrone! You must feed a stove more frequently to keep it going with fir, and there is no guarantee that there will still be live hot coals in the morning. Cord for cord the hardwood's may be a better deal.

    Hardwood's, like madrone, live oak, eucalyptus, walnut, black oak etc., are the choice of the serious fire burner. You may pay $300 for a cord of oak, and only $250 for a cord of fir. BUT, because the oak is more dense, it weighs much more than the fir. So you actually get more for your money with hardwood. In fact, you may get almost twice the fire for the money! Because hardwoods are denser, they provide more available fuel in the same space. So, hardwoods burn longer. If hardwoods are properly seasoned, they do burn very hot. (Look for oak mixed with madrone.) The fuel available in hardwood enables stoves or inserts to sustain high temperatures for significantly longer periods. Also, unless the stove is shut down tight, hardwoods may keep a hot live coal bed for days. So as a rule, airtight stoves, or inserts, perform best with dry hardwoods. It is, however, always important to have a large supply of really good kindling - because hardwood is difficult to start. Having a quantity of fir on hand is great source of good kindling.

    When buying firewood, remember that first and foremost, it must be properly seasoned. The best way to get seasoned wood is to buy THIS years wood for NEXT year! For a scrupulous first time wood buyer, a moisture tester may be a good investment. Wood sellers will often tell you that even though this wood was split this year, it will be just fine. Except in the cases of fir or pine, that is not true. Look for gray, or darkened, brittle wood that has a lot of cracks in the inner rings. Seasoned wood looks gray, or dark and dingy because it has been sitting sitting in the sun, drying, and collecting dust for a while. But, if you split it: it's dry and very WHITE inside! Unseasoned wood has the fresh clean look of new lumber at a building supply store. Unseasoned wood has that same fresh look on the INSIDE when it's split. Though seasoned wood is darker on the outside, it's bone white on the inside.

    Southern yellow pine: General rating good, heat produced good.

    Southern yellow pine rated as "good" firewood.

  52. Andrew Robinson | | #52

    Wood Stove water heaters?
    We are planning to heat a well insulated, air tight house with a wood stove - we live in Yellowknife, Canada where the design temperature is minus 45C. Energy modelling shows that we'll need ~32,000 BTU/hr at that temperature.

    The article mentions that in Sweden they recommend using a heat exchanger to capture excess heat and Tyler Forbes mentioned in a comment that wood stoves are being made with water jackets.

    I have not been able to find a single EPA approved wood stove (not a boiler/furnace) that has a water jacket or any way of heating water. There are lots to find in Austria & Italy, but no-one is selling them here?

    Anyone know why? Are EPA emissions regulations too strict for European wood stoves?

  53. User avater GBA Editor
    Martin Holladay | | #53

    Response to Andrew Robinson
    Cold water flowing through a coil in a firebox can change combustion characteristics, making it harder for a wood stove manufacturer to show compliance with EPA requirements.

    That said, it's possible to drill two holes in some models of stoves -- as far as I know, it's easier to drill holes in steel than cast iron -- and to install a stainless-steel coil in the firebox. This coil is connected (via a thermosyphon loop) to an elevated tank. Before you buy your stove, make sure that the firebox is big enough for this conversion, and that there aren't any firebricks in the way.

    Here are two suppliers of stainless-steel coils for this conversion:



  54. Andrew Robinson | | #54

    Wood Stove water heaters? I found one?
    Thanks for the links Martin,

    As you mentioned, adding a cold water loop to an existing stove would cool down the combustion gases with undesirable results. A large part of the improvements made to wood stoves in recent years focuses on increasing temperatures in the firebox by adding pre-heated secondary air. The results have been great reductions in particulate and creosote as well as increased efficiency.

    Cooling the combustion gases with a water loop would likely have the opposite effect - increased particulates, increased creosote and decreased efficiency. These loops would likely also void your warranty and potentially void your home insurance policy as well.

    But there are stoves out there that are designed with water heating in mind - sometimes they are called "Architectural Wood Boilers" - meaning they are a boiler that looks nice enough to have in your living room.

    In Italy: Lanordica ExtraFlame

    USA: Hydro to Heat Convertor - claims to have a model for Pasiv Haus - the Nano. Although the website says "coming in 2011"

    I tried to post links to the websites for the above sources, but the spam filter rejected the post :-(

    If anyone has experience with one of these, I would love to hear about it.

  55. User avater
    TIM MCCARTHY | | #55

    Any tips on punching a "zero" clearance chimney thorough a high performance roof. Roof has mentos at the top...intello at the bottom. Do we tape these layers to the chimney/roof adapter kit?

    1. Malcolm Taylor | | #56


      Depending on the adaptor there may still be a clearance to the combustable construction of the framing which might have to be bridged with flashing. Either the flashing or the air-sealing layer gets taped or caulked to the adaptor.

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