Wood stoves are Hal Richman’s business (he owns The Stoveworks in Chapel Hill) and I used to think his concern with safety was obsessive — until last week, when my friends’ home burned to the ground, probably because of a poorly insulated stovepipe. They lost nearly everything; the same day, when I bought a stove from Hal, I listened to everything he said. If you heat with wood, you should, too.
— Ed.
Heating with wood has become popular as an inexpensive, safe, and personally satisfying way of staying warm. Many people appreciate being able to keep their houses toasty without relying on the utility company or oil industry. Heating with wood brings us down to our roots — taking wood from the earth, gathering and storing it with our family and friends, sitting around a fire on a cold night.
The six great myths of woodstoves is that they are undependable, for one room only, hard to install, unsafe, dirty, ugly. Modern woodburning stoves don’t fit into any of these categories even though the old time, leaky chunk-burners might.
Since there is no thermostat, you are probably wondering how stoves work. The heat given off by a stove or fireplace is primarily radiant; the fire or stove radiates to us, the walls, the dog. Radiant heat is direct; convective heat, which involves heating air which is then used to heat the house, is indirect. Thus, the air in most houses with forced air heating systems seems stuffy and hot.
If your house is not designed for a radiant heat source like wood you can still heat most of it with one or more stoves, especially if you close off hard to heat rooms. Floor fans and vents in the walls can do wonders for moving hot air around the house. New houses can be designed to be adequately heated with one stove.
Since I am in the business of selling woodstoves and fireplaces, people are always asking me questions about wood heat. Here are some of those most frequently asked.
I know that fireplaces are inefficient, but I really like to see the flames. Are there stoves that offer both efficiency as well as a chance to watch the fire?
Conventional fireplaces have a net efficiency rating of around 15%. What many people don’t realize is that fireplaces use warm air from other parts of the house. Though you may be toasty in front of the fireplace, heating bills may possibly increase.
But you can still have the character of a fireplace and the efficiency of a high quality stove with fireplace-heater combinations like those produced by Morso, Efel, Jotul, and Fisher. All of these units allow you to keep the doors open for use as a fireplace or tightly close them up for use as an efficient, baffled stove that will burn unattended for a long time.
Can I put a woodstove in an existing house?
If you have an existing fireplace which is up to code, you are all set. Many heaters are vented low enough so the exhaust pipe can be inserted into the mouth of your fireplace. If you wish to install a stove that vents higher than your fireplace opening, it is possible to break into a masonry chimney at any point with a circular “thimble.”
However, if you do not have an existing fireplace or if you want to use your fireplace occasionally, prefabricated chimneys can be easily installed anywhere in your house. These chimneys also give you the flexibility of putting your stove where you want it.
Simple and low cost modifications in your home, such as fans and grates, can greatly increase the area that a single stove can heat.
Can I heat an entire existing house with wood?
Yes you can, but exactly how much of your house can be heated depends primarily on the size of the unit you purchase, the construction of your house (ducts, natural air flow between rooms), as well as how well insulated your house is.
Woodburning appliances like the Riteway can be hooked up to your existing furnace. However, if you don’t have a duct system and can’t get enough air moving through your house with fans and grates, then you can always install ducts and a wood or multi-fuel furnace (one that automatically switches from wood or coal to oil, gas, or electricity).
Which is better, a cast iron or steel stove?
Heavy duty cast iron and rolled steel are both satisfactory materials for a stove; one is not necessarily better than the other. Both are subject to cracking, warping, and rusting if they are of poor quality or used improperly. You will pay more at first for a durable, high quality stove but it will last, while a cheap stove will have to be replaced within a few years.
Can I buy a stove that can be used for cooking as well as heating?
If you are serious about cooking with wood, you should purchase a separate cookstove. The Autocrat and Preporod cookstoves are great for cooking, but do not have the duration of burning or necessary power to heat a living area.
Unfortunately, many people treat woodstove safety lightly. If a heating contractor came into your home you wouldn’t tell him to install an oil furnace without a chimney since you just wanted to run some stovepipe out the window. Maybe we imagine that things we can do for ourselves, like heating with wood, are second rate or somehow not real, and don’t give it the same respect as heating with a more acceptable fuel source like oil.
What is more unfortunate is that many people are risking their lives with woodstoves because of unsafe installations. If you are interested in learning more about woodstove safety read on. If you are heating with wood and are not interested, drive out I-40 or a back road and truck on at 90 mph and see how it feels. The risks are about the same.
Along with the increase in popularity of wood heat has been a proliferation of chimney fires across the country. Most building fires associated with wood heat are due to unsafe installations and carelessness, not any inherent danger in heating with wood.
You should comply with the standards set down by the National Fire Protection Association and all local fire, building and heating codes. They are usually reasonable. Read and follow the manufacturer’s recommendations for proper installation and use of the appliance you purchase. There are a number of good books on the market dealing with wood heat. The StoveWorks carries three excellent books: The Woodburner’s Encyclopedia, Wood Heat, and Modern and Classic Woodburning Stoves; we also have numerous pamphlets and articles on wood heat. This is an attempt to summarize some of the more important safety considerations involved in heating with wood and coal. These are only recommendations and suggestions; your local codes, NFPA standards, and manufacturer’s recommendations are what you should follow to the letter.
The protective wall covering you choose should be large enough and so placed that no unprotected part of the wall is within 36 inches of a radiant stove, 12 inches of a purely convective stove, and 18 inches of plain stovepipe. And this means any part of the stove and stovepipe. Some stoves, like the Efel, are not fully jacketed so you need to place them 36 inches away from any combustible surface.
Use non-combustible and non-conductive spacers for placing asbestos millboard away from the wall. Put an extra piece of millboard against the wall for added protection. This air space between the wall and the millboard is important since asbestos is fireproof but conducts heat easily. It is important not to place the millboard to the very top or bottom of a wall in order to allow for air flow from bottom to top.
I have heard of some manufacturers or importers recommending less clearance for their stoves. Unless this has been approved by Underwriters Laboratory disregard them and shop elsewhere. NFPA standards and local codes are what you should follow.
These standards may seem very conservative but they are not; the kindling temperature of wood drops from 750 F to 250 F when it gets dry.
Floor Protection
You need to protect the floor from radiant ignition as well as falling embers. The hearth (floor protection) should extend at least 18 inches in front of any part of the stove with openings or potential openings (including the back). Use 36 inches for the front of fireplace-heater combinations. The hearth should probably extend at least 12 inches beyond other sides of the stove.
No stove should be mounted on a bare floor, even if it has 18-inch legs. A stove with at least 4-inch legs can be mounted on a hearth consisting of sheet metal and a properly sized stoveboard filled with asbestos or gypsum. If there is carpet underneath, you had better put down a layer or two of bricks, although it is not necessary to sit the stove legs on top of the bricks if you are worried about venting the stove into an existing fireplace.
A stove with less than 4-inch legs should have a more substantial hearth than the one described above. It would be best in this case that the hearth be 18 inches above the floor, as it would have to be for a stove with no legs.
If your hearth is all masonry, it is important to seal all the cracks so no embers can fall through. Most people do not have adequate hearths because they are trying to vent the stove into the front of an existing fireplace. Do yourself a favor and have a thimble installed.
Chimney Connectors
Usually a few feet of stovepipe are used to connect the stove to the chimney and in such cases this section of the venting system is called the chimney connector.
You should use 24 or heavier gauge pipe; do not use galvanized pipe since it is possible that your stove will get hot enough to burn off the coating, which is toxic. The StoveWorks carries two brands of non-galvanized 24 gauge pipe.
Each stovepipe joint must be secured by three sheet metal screws placed on a triangular pattern around the pipe. If there is any way you can rivet or pop rivet the sections of pipe together, do it. Outside mechanical supports must be used if your chimney connector is longer than six feet but it doesn’t hurt to do it if it is shorter. The stovepipe should be accessible to inspection, cleaning, and possible replacement.
If you are venting your stovepipe into the thimble of an existing chimney, the pipe should be flush with the inner surface but not extend into the flue itself. This connection should be made secure with stove cement.
Again, any part of the chimney connector (composed of single wall stovepipe) must be 18 inches away from any combustible surface. Also, remember that a wall or surface with any combustible material in any part of it is considered to be combustible. Studs behind masonry or brick have been known to ignite.
A chimney connector cannot pass through a ceiling even if you maintain the 18 inch clearance; a fire can spread too easily through such a big hole. If you are passing Metalbestos pipe through a ceiling, you need to use a joist shield as a fire break. If the chimney connector is to pass through a wall it must be protected by maintaining the 18 inch clearance all around or by using a metal ventilated thimble whose diameter is at last 12 inches larger than the stovepipe diameter. Unfortunately, it is next to impossible to find such a thimble. A burnt fireclay thimble can also be used but must be surrounded by at least 8 inches of non-combustible material such as brick or asbestos millboard. If your present thimble does not meet these requirements, better get out your tool box.
Make your chimney connector as short as possible. Exposing more stovepipe will put more heat into your room, but it will do it very quickly as well as reduce your draft and collect more creosote. Don’t use any more than six feet of stovepipe in your chimney connector; a little more might be OK in a well-insulated house which will be kept warm all the time by a back-up heating system.
Avoid horizontal runs of pipe and keep the number of runs down to a minimum. Running your pipe uphill at about a 30 degree angle is best and running it downhill to the fireplace or a low thimble usually causes smoking. You can flange your pipes male to female coming out of the stove to guard against smoking or you can flange them female to male to guard against creosote leaking out. Choose your poison. But whichever way you choose, seal the joints with furnace cement and you shouldn’t have any problems.
The diameter of the connector pipe should be no smaller than the diameter of the flue collar of your stove; this means that you should not reduce an 8-inch pipe to 6 inches. Before expanding your thimble to 8 inches make sure your chimney is large enough to handle it.
Chimneys
Masonry chimneys should have flue liners, preferably fireclay (not terracotta) and preferably circular (not square or rectangular). The masonry should be structurally sound with no cracks — a very small smoke fire can help you detect any cracks. Even on an inside chimney it is helpful to insulate between the flue liner and masonry with vermiculite; it is imperative to do this with a chimney where one or more walls are exposed to the outside. But remember to leave some room for expansion and contraction of the flue liner if you are insulating or using cinder block holders.
If your chimney does not have a liner, put one in. The easiest, although most expensive route, is to fit Metalbestos prefabricated pipe down the chimney. If the masonry is large enough and there are no bends, an experienced mason can fit flue liners down an unlined chimney. You can also fit a heavy gauge steel liner down the chimney, it should be welded at the seams, not galvanized, and riveted at the joints. If at all possible insulate the space between the chimney and steel liner with vermiculite and make sure to put a waterproof seal and full protection cap (rain, wind, sparks) on the top. I have looked for heavy duty stainless steel pipe for this task but can’t locate any. The big problem with retrofitting a chimney with a steel liner is corrosion. My best guess is to paint the pipe inside and out with heat resistant, rust-proof paint like De-Rusto engine paint. Sherwin Williams markets a similar paint in gallon containers for use with a sprayer.
Combustible materials should be no closer than 6 inches from the outside of a masonry chimney. Exterior chimneys may be placed against a building’s sheathing.
If you are going to vent your stove from an existing fireplace opening you can’t use it as a fireplace. You can seal off the fireplace opening with sheet metal or asbestos millboard and insert a small amount of pipe into a circular hole in this covering. Use fiber rope for tight seals along the perimeter and where the pipe is inserted.
An alternative method, which I especially recommend when your fireplace has a metal liner, is to seal off the fireplace opening as described above and run stovepipe as far as you can to the flue liner. It is important to “flash” or seal off the pipe as close as possible to where it terminates to prevent against downdrafts. Furnace or refractory cement is a good sealant.
The first method of sealing your fireplace will leave creosote on the fireplace floor, the second method will collect creosote in your pipes. Whichever method your choose, make sure to inspect and clean the stovepipe and fireplace regularly.
If you are going to put a thimble in your flue, the space below the thimble should be filled with sand or gravel, leaving enough room for creosote and soot to collect without blocking your pipe. Clean this space below the thimble with an industrial vacuum before filling it up.
Don’t connect two appliances to the same chimney: 1) a number of chimneys can’t handle the volume of gases from two appliances; 2) the danger of sparks crossing over and your inability to control a chimney fire are quite serious; 3) older fossil fuel appliances may put out emissions which could combust with stove gases. If you do decide to do this, consult the NFPA standards and your local inspectors.
Chimneys must terminate three feet above the roof where they penetrate and must be at least two feet higher than the closest point on the roof within ten feet.
The only type of factory built chimney I consider acceptable for stoves is insulated pipe like Metalbestos or Metalvent. Triple wall or air cooled pipe was designed for free standing fireplaces and Franklins with high stack temperatures. Too much heat is lost from this type of pipe when using an efficient stove, resulting in a poor draw and higher creosote deposits.
Make sure to install your Metalbestos pipe according to the manufacturer’s directions and follow the necessary clearances from combustibles. This type of pipe is very efficient and usually much cheaper than a masonry chimney. On the negative side it is not a heat sink like masonry and is not designed to withstand the stress of a long term chimney fire, so keep it clean.
Any chimney will work better if it has no sides facing the outdoors. This also goes for Metalbestos, so keep as much of the chimney in the house as possible. If you visit New England you will see few chimneys exposed to the outside. Also, you should have some type of spark arresting screen on top of your chimney. The trick is to use rat wire or a screen which is large enough to allow free flow of the stack gases and small enough to deflect larger sparks. Many rain cap tops also deflect sparks back into the chimney. If you use a screen, inspect and clean it as often as you need to. What you really want is a cap and top arrangement which will protect against rain, wind, and sparks. The manufacturers of prefabricated chimney pipe make such caps, so ask for them.
Learn from our errors; don’t tighten the screw on the Metalbestos cap. It will never come off so you can clean the pipe. And while we are on the subject it is very, very important to clean your chimney. Check with us at StoveWorks about the best way to do it. I clean my chimney three times during a heating season. If you are new to wood heat or have a new chimney or appliance, I would check the chimney often, especially at the beginning of the season.
Chimney cleaning chemicals are not recommended. A good chimney brush, chain, and bag filled with chicken wire or pine cones will usually do the trick. Once you get the system down you can clean your chimney in no time. You will need to clean your chimney less if you collect less creosote in it. To reduce creosote:
Use dry, seasoned hardwoods; softwoods and minus woods are OK added to a hot fire as long as you don’t add too much.
Don’t “low burn” your stove too much.
Don’t fill your firebox all the way.
Use an insulated chimney or Metalbestos and as little chimney connector as possible (with as few bends as possible).
A few more points to remember:
If you are using a combination fireplace heater, treat it as a fireplace when using it open: watch out for sparks; do not leave the fire unattended without a screen; clean the ashes; open the main damper. When you shut your unit up, make sure it is tight.
Using two fireplaces on the same flue is a no-no. Block one up with sheet metal.
Set aside a special shovel and galvanized bucket (with a tight cover which should always be used) to collect your ashes. Even if you have an ash pan in the stove, you need to watch out for hot embers when disposing of the ashes or composting them.
Don’t “low burn” your stove all the time. This is when you have an airtight and close down the air inlet. If you use the stove this way, you won’t get as much energy out of the wood and will collect a lot of creosote. An efficient, airtight stove can reduce creosote deposits but when used in this way actually produces more creosote than your old chunk-burners. Burn your stove at a moderate rate most of the time.
Make sure all doors, etc. are closed tightly. Use special fireproof gloves whenever necessary.
If you have children, teach them about the stove and the possible dangers. A circulator like the Shenandoah or Autocrat are safest, the outer jacket doesn’t get all that hot. A heavy cast iron stove will have a lower surface temperature than most well made sheet steel stoves, and thin walled stoves get quite hot.
Don’t use any fluid or contraption to start the fire.
Don’t use the stove as a trash burner. You’ll get a lot of creosote and ash as well as plastic residues in the ash.
Keep all combustibles, including wet wood, a good distance away.
Keep ABC fire extinguishers at crucial places around the house. Provide for fire escapes (like rope ladders) and make sure all windows in the house can be easily opened; if necessary keep a hatchet nearby.
Check your stove for cracks, faulty doors, etc. Furnace cement does crack so re-check periodically.
Double check your stove before you leave the house. Make sure all the doors are tightly closed, all combustibles are away from the stove, the damper and air intake are set properly, etc.
Consider a smoke detector. Check with your local fire department for more details.
Above all, don’t be careless or complacent even if you have the safest installation going. And stay warm!
Stove Clearances
Radiation from large hot surfaces can be hot enough to start a fire. The following table, which appears on page 69 of the Woodburner’s Encyclopedia, is adapted from the NFPA standards mentioned above:
| TYPE OF PROTECTION3 | STOVES4 | STOVEPIPE5 | |
| Radiant6 | Circulating6 | ||
| Unprotected | 36” | 12” | 18” |
| 4” asbestos millboard | 36” | 12” | 18” |
| 1/4” asbestos millboard spaced out 1” | 18” | 6” | 12” |
| 28 ga. sheet metal on 1/4” asbestos millboard | 18” | 6” | 12” |
| 28 ga. sheet metal spaced out 1” | 12” | 4” | 9” |
| 28 ga. sheet metal on 1/8” asbestos millboard spaced out 1” | 12” | 4” | 9” |
TABLE 9-1. NFPA Recommended Minimum Clearances From Combustible1 Walls and Ceilings2
1Combustible materials include wood, cloth, vinyl, paper, etc. Wood covered by plaster is also considered combustible. Thus, of the most common wall and ceiling constructions, only masonry walls are excluded.
2Adapted from National Fire Protection Association Standard No. 89M, “Heat Producing Appliance Clearances” (1971).
3Protection should extend over enough of the wall or ceiling that no uncovered part of the surface is closer than the “unprotected” clearance.
4These are clearances from the sides and rear of a stove. Slightly different standards exist for the tops and fronts of stoves, but they are almost always met in practice (stoves are rarely placed close to ceilings and the space needed in front for loading is normally more than ample for safety). See NFPA 89M for details.
5These are clearances from a parallel wall or ceiling. See text for case where stove pipe passes through a wall or ceiling.
6Most stoves are classified as “radiant.” “Circulating” stoves have outer jackets all around the stove with openings, usually grilled, to allow air to circulate. An example is the Shenandoah R-76 console model.
