How To Improve Wood Stove Efficiency

Get the most efficiency and benefit from your stove.

Stove fires can occur from improper installation and maintenance. Always respect the necessary clearances from combustibles and ensure that your stovepipes and chimney are in good repair.

Getting the most out of a woodstove means more than simply stoking the fire.

The kind of stove you buy, where you locate it in your house, the wood you choose, where you buy your wood, and burning techniques — these all determine how efficiently your woodstove is working.


Chimney efficiency really means wood heating system efficiency. Components of this system are:

  • The stove

  • Chimney and smoke pipe

  • The house

  • Fuel

  • Weather

  • Stove operator

These components are so interrelated that they're inseparable. For example, a highly skilled stove operator would have great difficulty maintaining a good fire with green or wet wood in a bad stove with a very short, exterior chimney.

On the other hand, an operator with no experience could get into serious trouble with an otherwise excellent system.

An ideal system would include:

  • An interior chimney of sufficient height — 12 feet or more — the top of which is 2 feet taller than anything within 10 feet of it, such as the roof or another building.

  • Less than 7 feet of stove pipe with no more than two elbows so smoke doesn't cool too much before it gets to the chimney.

  • A modern, certified stove well-maintained and sized correctly to the house/room.

  • An experienced operator who likes running the stove and follows the instructions in the owner's manual.

  • A house with an open floor plan so that the stove can be run comfortably at temperatures hot enough for efficient operation.

  • Dry wood — containing 15-20 percent moisture content — split small enough so that several pieces can fit in the stove at once.

  • Cold weather. Draft is a function of the temperature difference between inside and outside. Warmish days do not promote good draft and, worse, if you run your stove when it's 55 degrees out, you'll quickly get too warm and shut down the air inlets to cool off the fire. That's a recipe for creosote formation.


There's more to locating a wood stove in your house than you might suppose. You need to consider these questions:

Where is your chimney? Unless you're prepared to build a newone to accommodate your stove, this can be a limitation as it's unwise to have more than 7 feet of stovepipe connecting the stove to the chimney because of excessive creosote buildup and instability.

How close would the stove be to combustible material, such as walls, doors, and furniture? Most stoves need to be 36 inches away from anything that can burn. Reduce a stove's clearance from 36 to 12 inches by installing a heat shield of 28-gauge sheet metal, mounted off the floor to provide 1 inch of unrestricted air circulation between it and the wall.

Is it your intention to heat your whole house with your stove? If so, then having the stove as near to the center of the house as possible makes obvious sense, because woodstoves are not central heating devices designed to circulate heat to remote corners and rooms. Some houses are not great candidates for being completely heated by a woodstove because they're too large or have many interior partitions. In that situation, consider putting the stove where you spend most of your waking hours.

How big is the room where you want to put the stove? Any model capable of significant heat output will, if run correctly, overheat a small room. If small rooms are all you have or, for whatever reason, a small room is otherwise the only good location for a stove, get a small stove. Your stove dealer or installer should be able to help you assess your options.

Do you care about just the heat, or do you want to enjoy the fire? Some houses, particularly those with many interior partitions and/or are one story, are best heated by a stove in the basement. Bear in mind, though, that sitting in front of a basement stove might not be enjoyable.


Basement installations, particularly in tightly-constructed houses, can be plagued by poor draft. Warm air that rises from the basement creates pressure differences in various levels of your house; pressure in the basement is less than the outside atmospheric pressure, which can create "negative pressure."

Negative pressure can make a substantial difference in a heating stove's venting. Wood-burning stoves located in basements are susceptible to backdrafting problems, in which the stove "puffs," or emits puffs of smoke.

Before you install a stove in your basement, get a chimney sweep or stove installer to help you figure out if negative draft is going to be a problem.


Which types of wood are best for heating? The short answer is seasoned hardwood, but the more useful answer is a little more complex.

In the first place, different parts of the country have different species of trees, so a woodburner's choices are limited by geography. It's a cruel fact that the colder the climate, the less heat value in the commonly available wood. In Alaska, for example, you would likely have to burn some variety of softwood — spruce, fir, pine, and the like — with a heat value per cord equivalent to 115-140 gallons of fuel oil. In the southern United States, you might burn hickory, with nearly twice the heat value.

In the second place, your heating needs will vary considerably over the course of a heating season. In central Vermont, where I live, this season extends from October through April, from 40 degrees above zero to 20 or even 30 degrees below. Clearly, the wood that is perfect for one extreme is not ideal for the other, so having a variety of wood types is your best bet.

My woodpile for the upcoming winter contains both red maple (one cord=190 gallons of oil) and American beech (240 gallons). I even try to guess, when I'm piling, where to put which varieties so that I'll come upon the wood appropriate to the weather. I'm always wrong, but you get the idea.

Generally, very high-heat-value woods (equivalent to more than 220 gallons of oil per cord) which include hickory, apple, white oak, beech, and hornbeam, will give you steady fires of long duration and create deep beds of coals.

The low-heat-value woods (less than 140 gallons of oil per cord), which include most softwoods, poplars, basswood, and butternut, burn fast and make few coals.

Usually, having a variety of wood in your woodpile and in your stove will work best. I've tried filling mine with hickory on very cold nights only to find the stove so full of coals in the morning that there wasn't room to add wood, and the coals weren't throwing enough heat by themselves to keep the chill out of the air. Hickory mixed with less-dense woods, on the other hand, works very well.

A word about softwood: Avoid burning it if you can, except for a modest amount as kindling. It's tricky to burn properly because, although it burns up quickly, it also burns very hot, because of its pitch content. You could damage your stove or start a chimney fire unless you drastically reduce the fire's air supply, and then you have to worry about rapid creosote formation.

If you know nothing about which woods in your area are best for burning, it's worth taking the time to talk to experienced woodburners and/or state foresters to get an overview. As you gain experience, you'll develop your own likes and dislikes.


In purchasing wood, two issues are primary: Quantity and quality.

Quantity. Wood is generally sold by the cord, which is 128 cubic feet or, more properly, a closely piled stack which measures 128 cubic feet, commonly a 4x4x8 tier. In some areas, dealers sell "face cords" which are usually less than a full cord. Be clear about what you are paying for. Also, familiarize yourself with what a cord looks like when it isn't stacked, because firewood is often delivered dumped in a pile.

Ask potential dealers how they determine the quantity of wood that they're delivering. If they tell you that their truck bed measures 128 cubic feet, beware; if they stack the wood on the truck, it will be a cord. But if they toss it on or dump it on with a loader, it's apt to be two-thirds or three-fourths of a cord.

Quality. Quality has two components: variety and degree of seasoning.

You should reasonably expect a mix of your area's predominant wood species. You need to ask, though. Firewood dealers can sell only what they happen to be cutting.

I strongly advise you to buy green (unseasoned) wood, and buy it enough in advance of the heating season so that it will be dry when you need it. In my experience, very little of the wood sold as seasoned really is, and it costs much more than green.

I'm not accusing firewood dealers of dishonesty, by the way. There's a good deal of misunderstanding about what constitutes seasoned wood.

The difference between green wood and seasoned wood is water, nothing else. Green wood is 50 percent water, and dry wood is 15-20 percent. Wood doesn't lose much water until it is cut to length, split, and stacked under cover. The clock doesn't start ticking the minute the tree is cut or, if it does, it's ticking slowly. Many firewood dealers, not knowing exactly how much of each length of wood will be ordered, don't buck and split it until it is ordered, so it will take quite some time after delivery for it to dry.

Before ordering, make sure the wood will fit your stove's specs.

"United States Stove Company states its maximum log length in all of our descriptive literature," says Rodger Castleberry, the company's VP of Sales and Marketing. "We don't want someone to assume that they can burn a 30-inch log in an appliance that can take a log only 24 inches long."

If you don't have that literature, simply measure the firebox to determine wood length, he says.


A proper fire is an active fire. Smoldering, slow fires should be avoided because they can cause heavy creosote buildup, which creates a fire hazard.

Roaring fires are also a bad idea, because they can damage the stove and chimney, start a chimney fire, and waste wood, since they send most of their heat up the chimney instead of into the house.

"A roaring fire will diminish life expectancy of the stove or furnace," notes Rodger Castleberry, VP of Sales and Marketing for United State Stove Company. "A roaring fire should occur only during the brief time when starting or re-starting a fire."

In an active fire, there will be some flame and little or no smoke in the firebox of the stove. A magnetic surface thermometer, which you should have, should read somewhere between 250 and 475 degrees once the fire is established. Note that the surface reading is a little more than half the temperature in the stove.

You maintain a good temperature by regulating the air supply and the wood supply. Generally, adding small amounts of wood at fairly frequent intervals will better maintain a clean, active fire than will loading the firebox, burning it down to coals, and loading it again.

Stoking a stove for an all-night or all-day burn is a compromise between the two loading techniques. Load the stove for the extended burn with multiple stokings during the hour or so before you leave the stove. Note that an "overnight burn" probably won't mean that you have an active fire eight hours after you shut it down, but you should have a good bed of coals and little difficulty getting an active fire going again.

These are general guidelines, and because stoves behave differently, you should refer to your owner's manual for advice specific to your stove.


That heat stove you've had your eye on may be much more affordable than you realize.

You can claim a 30 percent federal tax credit — capped at $1,500 — on the purchase and installation of an approved 75 percent efficient biomass-burning appliance under the American Recovery and Reinvestment Act of 2009.

"That means you could spend $5,000 on the entire thing — stove, installation — and get $1,500 back in a tax credit," says Rodger Castleberry, VP of Sales and Marketing for United States Stove in South Pittsburg, Tenn.

Under the guidelines, if you spend $3,000 to buy a stove and have it installed, you can claim a $900 tax credit; if you spend $4,000, you can claim a $1,200 tax credit.

Homeowners should consult their tax adviser to properly receive this tax credit, Castleberry says.

For a list of United States Stove's products that meet or exceed the guidelines established by the IRS, visit

For details of this tax credit go to


High heat value

1 cord = 200-250 gallons of fuel oil or 250-300 cubic feet of natural gas

  • Hickory

  • Oak

  • Ash

  • Sugar Maple

  • Beech

  • Yellow Birch

  • Hornbeam

  • Apple

Medium heat value

1 cord = 150-200 gallons of fuel oil or 200-250 cubic feet of natural gas

  • White Birch

  • Red Maple

  • Big Leaf Maple

  • Douglas Fir

  • Eastern Larch

  • Elm

Low heat value

1 cord = 100-150 gallons of fuel oil or 150-200 cubic feet of natural gas

  • Aspen

  • White Pine

  • Hemlock — Western and Eastern

  • Western Red Cedar

  • Red Alder

  • Redwood

  • Sitka Spruce

  • Cottonwood

  • Lodgepole Pine

Source: The Harrowsmith Country Life Guide to Wood Heat by Dirk Thomas

Story by Dirk Thomas

Illustration by Tom Milner

#wood #firewood #woodstove #heating #fireplace

20 views0 comments

Recent Posts

See All

The Big List of Wood Heat Tips For peak efficiency and convenience Ensure safety first, then higher efficiency is possible To operate your wood heating system efficiently, you must have confidence tha

Can Firewood Be Too Dry? Yes, although it is not a common problem Properly seasoned firewood still has a fair amount of water in it, say 15 to 20 percent of its weight. That water regulates the combus