Choosing a Wood-Burning Stove for Your Home
By Karen Keb
Woodstove smoke is a welcome sight on a blustery winter day.
If you’ve picked up this magazine, you’re probably the type of person who likes to do things for yourself: You’ve taken steps to become more self-sufficient and rely less on big industry. With the garden in place and the livestock munching grass in the field, it might be time to turn your attention to the farmhouse and its systems, and explore some ways to become more sustainable there.
Never before has the cost of home heating been so high. The price of nonrenewable home-heating fuels such as propane, fuel oil and electricity is surging due to dwindling resources and higher demand. In hard times, we inevitably return to the wisdom of our ancestors. Before having access to electricity and propane, people chopped wood and heated their homes with fire.
There’s nothing quite like the crackle of wood when it catches fire, the smell of smoke rising through the chimney, and the glow of embers on a cold night. A wood fire warms body and soul, the flames provoking thought and providing solace. And if those flames are capturing your imagination inside a woodstove, you’ll hear only their spit and snap — not the whir of your HVAC churning (i.e. money burning) to keep your home comfortable. By choosing to zone heat your main living area with a wood-burning stove, you’ll substantially cut your fuel bills whether you buy wood or grow and harvest it yourself.
Compared to open fireplaces, woodstoves are incredibly efficient at heating a room. Fireplaces create ambience; woodstoves create heat and ambience. The usual home fireplace converts only 10 to 20 percent of the wood burned to heat, whereas wood-burning stoves commonly achieve efficiencies of 50 to 77 percent. A woodstove can heat a single area or an entire home, depending on the size you choose and where you place it. It also has the added benefit of being able to heat your home even during a power outage.
Types of wood-burning stoves
There are three major types of woodstoves: circulating stoves, radiant heaters (“potbellied” stoves), and combustion stoves (“Franklin type”), with circulating stoves typically having the highest efficiencies. Circulating woodstoves are double-walled with an inner combustion chamber, usually made from cast iron. An outer shell of sheet metal promotes airflow over the inner shell, and the room is heated primarily by this heated air, while the outer shell stays relatively cool. The airflow around the inner chamber enables sufficient heat extraction to result in efficiencies of up to 70 to 80 percent. With a circulating stove, you can control draft and heat output with a damper, and some units have a fan that provides even more convective airflow.
If you have an open fireplace and would like to make it more efficient, a woodstove insert can be installed, which will help eliminate drafts, keeping more of the heat out of your chimney and in your home.
Picking installing a wood-burning stove
When choosing a stove, there are a few important things to know. Cast iron is generally accepted as “top of the line” material when it comes to woodstoves because of its ability to warm up slowly and retain heat well. However, cast iron is fairly brittle and subject to cracking if not handled with care. Bear in mind that stove ratings can be fairly useless because there are so many different rating systems, and testing conditions are usually not stated. Select a stove size based on your available space and the required clearances around it. You’ll want the stove to sit in the center of the area to be heated, and be ideally situated so that the heat will be picked up by an existing central heating cold-air-return system and circulated through the house.
Unless you have some experience with both interior and exterior remodeling and local fire code, it’s probably a good idea to get a skilled and certified professional to help make sure your woodstove installation gets done safely and properly. To reduce the possibility of fire, the National Fire Protection Association (NFPA) recommends that woodstoves maintain safe distances from combustible walls and surfaces. This means the stove must be backed by and seated on noncombustible materials such as tile, stone, brick, etc. Prefabricated stove boards also exist if time or budget prohibits a build from scratch.
Before you commit to a woodstove, consider the following:
• Make some phone calls to your homeowners’ insurance company, and to a local building inspector to make sure a woodstove can be installed in your home without major premium increases or cost-prohibitive remodeling.
• Look for a wood-burning stove that is listed by Underwriters Laboratories or another nationally recognized testing agency that uses the same standard.
• With the help of a certified chimney service, determine whether your existing chimney can be used, if you have one, or if an approved chimney can be built for your stove.
• Shop around for stoves; consider the different types discussed above, and examine the quality of workmanship of each stove you consider.
If your home is older and has a fireplace, most likely you have a masonry chimney — constructed from noncombustible masonry materials such as brick, concrete block or stone. Since masonry chimneys are usually the heaviest part of the house, they must be constructed on a concrete footing heavy enough to support the weight without settling. These chimneys are usually lined with smooth, vitrified fire clay tile (flue tile) that is designed to withstand rapid fluctuations in temperature without cracking.
The opening in the chimney through which smoke passes is called the flue. Smoke moves up the flue in a swirling pattern, so round flues perform better than square or rectangular ones because there is little obstruction to the natural flow of smoke. In order for smoke to pass and drafts to develop adequately, flues must be sized in relation to stove capacity and chimney height. As a rule, flue size must be 25 percent larger than the size of the stovepipe, which connects the stove to the chimney. For example, a stove with an 8-inch diameter pipe would require at least a 10-inch flue.
By installing a special chimney liner, you can convert an old masonry fireplace chimney for use with a wood-burning stove, but after the conversion is made, it cannot be used as a fireplace (in general, only one solid-fuel-burning appliance can be connected to a chimney flue). The NFPA recommends that each stove or fireplace be connected to a separate flue; this reduces interference between units and increases the efficiency of each stove.
Maximum burning efficiency is obtained when chimneys are located as close as possible to the stove unit, and when stovepipes are short and straight. The usual recommendation is to limit the length of connecting pipe between stove and chimney to 10 feet and with no more than two 90-degree bends.
If your home doesn’t already have a masonry chimney, you can have one built, or have a prefabricated metal chimney unit installed for a woodstove. Prefab chimneys are easier to erect than masonry, and will generally cost less than retrofitting a masonry chimney. Prefab units are relatively lightweight so no heavy footing is required, and they can often be installed through a room corner. According to the University of Missouri Extension, tests by the National Bureau of Standards indicate similar performance for prefabricated and masonry chimneys when used under similar circumstances. In addition, prefab chimneys used for wood-burning stoves must bear the Underwriters Laboratory (UL) listed label and be designated as “all fuel” chimney units. UL-listed “vent” type units are not satisfactory for use with woodstoves.
There are two types of prefab chimneys available today: the insulated unit and the triple-walled unit. Insulated units consist of an inner and outer layer of metal (usually stainless steel) with the space between filled with one or more inches of noncombustible insulation. Triple-walled units have three layers of metal and are designed so that air circulates between the outer two layers and removes excess heat — insulation is sandwiched between the inner two layers. Check local codes and consult with a professional to determine the right prefab chimney for your situation.
Enjoy the warmth
No matter what kind of wood-burning stove you choose, you’ll be warmed by the knowledge that your home is being pleasantly and efficiently heated in the same wonderful way as those of your forebears — fueling with inexpensive, sustainable wood.
Karen Keb is the editor of Heirloom Gardener magazine and blogs at My Home Farm.
Our farmhouse chimney
As the third owners of a 106-year-old four-square farmhouse in Kansas, my husband and I assumed there wouldn’t be too many layers to peel back to restore it to its former glory. Wrong! At some point in our house’s history, its old cookstove chimney was filled in with concrete and covered up by a large, built-in, unsightly cabinet — from the looks of it, it was probably in the 1970s. Wanting to get off the propane truck and utilize some of our free renewable wood for heating, we embarked on our own chimney-woodstove project.
We began by ripping out the cabinet and exposing the old chimney. Next, a firefighter/certified chimney sweep inspected the chimney and determined it was safe to use with the proper amendments. A 10-inch diameter hole was made in the chimney to accept the stovepipe, and a stainless steel insulated liner was run up the length of the two-story chimney. Some repairs were made around the exterior of the exposed chimney, and a new chimney cap was installed.
The next and most lengthy step was deciding upon and building the hearth. We originally wanted to use the limestone found in the fields all over our farm, but after realizing how this would require additional shoring up of the footing due to the weight, we opted for manufactured stone in order to cut our costs. Once we selected the stone, our contractor crafted a lovely hearth and travertine floorboard for the stove to sit on. One unique feature our contractor, Mark Schafer, engineered was the travertine floor to sit flush with the existing hardwood floor, eliminating stubbed toes and traffic problems of elevated stove boards or hearths. He carved out the wood floor and subfloor in a beautiful curved shape, installed two layers of cement board underneath, and placed travertine on top (to satisfy code), cut in the same pattern.
The complexity of codes that dictate fire-safe distances from combustible walls and surfaces was mind boggling. No matter how many times we thought we had the measurements correctly figured, we’d come up wrong. Your county will have building codes, the National Fire Protection Association has recommended minimum clearances, and your homeowners’ insurance company will definitely have requirements that will need to be met if you expect to be insured for fire. When it comes to fire, it’s always better to be safe than sorry, so measure five times and cut once! Always use a conscientious contractor in conjunction with a certified chimney sweep to get this kind of job done.
We purchased a used cast-iron Hampton woodstove that had been completely refurbished by a certified chimney sweep, who installed it and guaranteed it for life. We expect to recover the cost for the entire project in less than three years based on a propane cost of about $2 per gallon, but the joy of growing our own heat and the beautiful wood fire it produces is truly priceless.
Best wood for burning
If you live on a farm, you’ll undoubtedly have access to firewood year-round. Whether you have thick hedgerows to harvest from or you have fallen limbs from the last big storm, wood is usually plentiful and free. But some wood is better than others when it comes to burning in a stove. Here are some guidelines:
The type of wood is not as important as whether it has been properly dried, or seasoned. All wood — from pine to oak — should be set to dry and season for at least one full year before burning. Properly seasoned wood produces the hottest and cleanest fire with the least amount of creosote buildup.
Green (unseasoned) wood contains high levels of moisture that make it frustrating to use. It will be harder to light and may smolder, and it won’t put out as much usable heat. Lower temperature fires can lead to creosote buildup in your chimney. (Creosote buildup is dangerous and can cause a chimney fire if left unchecked, which is why a professional chimney sweep inspection is recommended once per year.) If you burn considerable unseasoned wood, you will want to allow for periodic hot burns to help avoid dangerous creosote buildup.
Cut and split your wood this year for next winter — wood that hasn’t been split will be slow to dry.
Covering your firewood with a tarp is not ideal. It will hold moisture and prohibit evaporation. Stack wood in a shed or a sheltered wood crib.
Wood deteriorates after 4 to 5 years, with the best burning wood being 2 to 3 years seasoned. Keep in mind that if you must buy firewood, most wood for sale is “this year’s” wood; to be on the safe side, buy wood this year and season it for next year. When you get serious about heating with wood, you’ll need to think one full year ahead.
There is so much to say about hardwoods versus softwoods, but for the sake of space, just know that hardwoods are usually denser, meaning they provide more available fuel in the same space and burn longer. Properly seasoned hardwoods burn very hot, and this fuel enables wood-burning stoves to sustain high temperatures for longer periods of time. As a rule, airtight stoves or stove inserts perform best with dry hardwoods.
However, because hardwood is difficult to start, always have an ample supply of good kindling — fatwood, black-and-white (not glossy) newspaper, and dry fir splits all make excellent kindling.
Learn more about firewood options in our Find the Best Firewood for You BTU comparison chart.