Wood Stove Safety
From the time you purchase your wood stove through the duration of its use, certain safety precautions should be taken. Here, you'll find a few general tips to carry you through the purchase, installation and maintenance of your wood stove as well as some guidelines to follow should your prevention measures fail and you're faced with a dangerous situation such as a chimney fire. Keep in mind these are just general guidelines. We recommend you have your wood stove installed by a certified installer, or, at the very least, contact your wood stove retailer, a certified installer, or your building code enforcement officer for more information. You can find certified installers through The National Fireplace Institute.
Because safety is such a broad topic, only a few aspects of it are being covered here. For information on logging or wood sourcing safety, please see the links & resources to the left of this page. Burn safety & air quality concerns have been dealt with on separate pages within CCE's website.
BUYING YOUR STOVE
- Be sure to buy a wood stove that is the correct size for your heating needs. If the stove is too small, you will be tempted to run it hotter than it should be in order to attain the heat you need. This overfiring can overheat and damage the stove itself as well as stovepipe parts and adjacent structures in your house, which could cause a house fire. If the wood stove is too large and you reduce its output by restricting the air supply with the damper, then underfiring occurs. Underfiring reduces your stove's burn efficiency, creates a good deal more smoke and causes creosote to form more rapidly on the stovepipe. Creosote buildup is the main cause of chimney fires: the creosote is combustible, so once it has built up, one hot fire can cause all that creosote to ignite, dangerously raising the temperature in the stovepipe or chimney and potentially igniting adjacent structures as well (see below for more on chimney fires).
Check the wood stove carefully for deterioration or damage (cracks, warped components, etc.)! If you're buying a used stove, avoid buying anything made before 1990. Around 1990, EPA Phase II standards kicked in, requiring wood stoves to meet stricter emissions standards. Most older units are significantly more polluting than those made after 1990, affecting both indoor and outdoor air quality. They are also more inefficient, which will increase your fuel costs. So, make sure the wood stove bears the EPA Phase II-certified sticker. Newer stoves are a little easier to shop for. Underwriters Laboratories or another institution like UL should have given its approval to any new stove you're looking at. This certifies that the stove meets safety standards. Again, always look for the EPA Phase II-certified sticker. (The EPA is working on even stricter emissions standards, which may be in effect as early as 2012.)
- Check your wood stove manual and always follow clearance guidelines specific for your wood stove. If your application requires tighter clearances, talk with your wood stove retailer about factory-made heat shields specific to your stove, or he or she may be able to manufacture an appropriate shield to attach to the adjacent wall(s).
- Make sure the floor under where you intend to set the wood stove is strong enough to support its weight, and then build or buy a hearth to set it on. Non-combustible flooring must extend under the entire stove, continuing for 12" past the sides and 18" in front of any loading doors.
- Technically speaking, stovepipe is single-walled, usually black metal pipe that can only be used to run from the wood stove to a couple of feet before a wall or ceiling. A Class "A" chimney--either double or triple-walled high-temperature stainless steel--must be run the rest of the way (through floors, walls, ceilings, and between floors). Run the stovepipe and chimney in the shortest route possible--this will improve your draft and reduce turbulence in the exhaust gases, making your installation safer. Also, as the length of the pipe increases, it becomes more likely that its joints will deteriorate over time. Limit the number of bends you use and make them curve as gradually as possible. If you're doing the installation yourself, check with your local building inspector and your local wood stove retailer to make sure you are complying with established safety standards.
- If you have an existing chimney that was built for a gas, oil or coal furnace, chances are it will not be suitable for a wood stove, at least not without some modifications. First, most chimneys are over-sized for wood stoves, which will give you a poor draft and increase creosote buildup. Second, proper clearances to combustibles (wooden framing) are often not maintained. Third, if it's a masonry chimney, most are not lined with a proper flue liner. And fourth, many masonry chimneys develop cracks in the mortar over time, which will allow air leaks, reducing draft, allowing smoke to escape, and creating the potential for hot flue gases to contact combustibles. If you'd like to use your existing chimney, have a certified installer take a look to see what you have. If it's metal, your options are somewhat limited. If it's masonry, you will probably have to reline the chimney with stainless steel pipe. Place an appropriately sized cap on top of the chimney. Poisonous gases or sparks may pass from one heating device to another, so don't connect more than one appliance to the same chimney flue.
- When putting the stovepipe and chimney together, mount the female ends of the pipe sections up to prevent creosote from leaking out around the seams and then seal each junction to keep the smoke from escaping. Use black surface cement, which can be purchased from your wood stove retailer, for this purpose.
- Building a "crud trap" into your system allows you easy access for cleaning out your stovepipe. Usually, this is built into the longest run of stovepipe. Also, if your stovepipe exits your stove out the back (rather than the top), instead of placing an elbow where the pipe leaves the stove, put a tee fitting there. If you put a removable cap on the lower end of the tee (be sure to fasten it with sheet metal screws) then cleaning the stovepipe is much simpler.
- Keeping your stovepipe running through your house and out the roof is better than running it outside through a wall. Cool outdoor air causes outside chimneys to experience a cooling effect which makes the chimney about 20% less efficient & encourages rapid creosote formation.
- Stovepipe thermometers are a cheap and easy way to monitor flue temperatures. They give you an easy way to make sure you are not firing your wood stove too hot (which may cause stove or stovepipe damage and could ignite adjacent structures) or too cold (increasing smoke levels and allowing creosote to build up). Check with the manufacturer or your wood stove dealer for best placement (most are screwed into the stovepipe or attach magnetically about two feet above the stove's top).
- It's always a good idea to install a gate or small fence around your wood stove, especially if you have small children or you are going to have small children in your house.
Have your chimney and wood stove inspected by a certified chimney specialist once a year, well before the heating season. If you would like, there are a few simple checks of your chimney and stovepipe you can do yourself (see our Proper Maintenance pages for more on maintenance of your wood stove):
- Stovepipe can deteriorate over time, so you should test the soundness of your pipe on a regular basis after the first year or two of use. You can do this by simply squeezing the pipe: the walls should not be crushable; if you can crush the walls then the creosote has eaten away too much metal for the installation to be safe.
- To test the soundness of a chimney, plug the top of the flue then start a small smoky fire below. The smoke will puff out of any leaks that the chimney liner contains. This technique is known as puffing.
- Before firing up the stove, check the amount of creosote accumulation. More than 1/4 inch of creosote is considered hazardous and should be cleaned out before your next burn. Perform the check for creosote every two weeks until you have become accustomed to the stove's behavior. You can do this by peering into the system or by tapping on pipe sections with a metal object. Once you're used to the ringing sound that a clean pipe makes, you should be able to distinguish the dull thud of a dirty one.
Chimney fires are caused by an accumulation of creosote on the stovepipe or chimney. Creosote is made up of condensed volatile gases created by incomplete combustion of the wood. As these gases rise in the chimney, they cool, mix with water vapor, and form a tar-like substance that clings to the chimney walls. When sufficiently heated, through normal wood stove operation, the creosote can ignite, causing a chimney fire.
Chimney fires can start quickly and be very powerful, shooting flames many feet above the chimney cap and producing a loud rumble like a freight train going by. They can also be less dramatic: slow-burning chimney fires don't get enough air to become "ragers". But they can still reach excessively high temperatures and can cause as much damage to the chimney structure and nearby combustible parts of the house as their more spectacular cousins. With proper installation and chimney care, chimney fires are entirely preventable, but if you are faced with one, here is some basic information about them.
- Chimney fire signs
- The chimney is emitting sparks
- The stovepipe is exceedingly hot, maybe even glowing
- Air is rushing through the draft in the stove
- Loud cracking or popping noises can be heard or you hear a rumbling like that caused by a low-flying plane or a freight train
- If you have a chimney fire
- Call 911 and get yourself and your family out of the house.
- If the fire has just kicked in and only if it is safe to do so, before leaving the house you should close up the stove to starve the fire of oxygen.
- Never pour water into the stove! The rapid cooling of the stove's body can cause it to crack, which will only aid oxygen flow to the blaze.
- If oxygen is leaking up to the fire through a crack or other imperfection in the stove then flashing can occur (brief, very hot ignitions caused by the influx of oxygen). Repeated flashing can tear apart masonry chimneys and stovepipes. If you suspect that flashing is occurring, the best line of defense is to leave the dampers open.
- Retreat a safe distance from your home and wait for the fire department to arrive. Even if it looks like the fire has burned itself out, don't return until they have done a thorough check of your house. Spray your roof--not directly on the chimney--with a garden hose to help limit the possible spread of fire. Even if flames have stopped shooting out of the top of the chimney and the rumbling noise has stopped, there may still be enough heat on or near combustible parts of your house to ignite them.
- After a chimney fire, have a certified installer or chimney sweep do an extensive cleaning and check of your system for soundness. The blaze likely transformed any creosote within your chimney into a thicker, crustier layer which will cause extremely rapid creosote accumulation during your next burn if left in the chimney. The stovepipe and chimney may also have become damaged by the fire.