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ARTICLES - - Wood Stove Wall Clearances - Primer

Written by Ken Rajesky, Hearth Industry Expert.

After the difficult decision of what stove to buy has been made, you’ll need to install the stove safely. However good the stove is, it’s still not safe unless installed to manufacturers specifications.

First, review the owners guide that came with the stove. Discuss the installation with your retailer. If you have further questions, contact the technical service department of the manufacturer. The Hearth.com Forums (on this site) can also help you get answers about stove clearances.

What is a Clearance?

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Firebrands and test booth wall
w/temperature probe wires

A clearance is the safe distance from the stove to a combustible surface. Examples of combustible materials include paneling, wood, sheet rock (even fire rated), and plaster (lathe). Safe clearances for your model were determined using a very specific and detailed U.L. protocol test procedure. The stove was placed into a wooden booth where the walls are on tracks allowing them to move back and forth. Heat sensing thermocouples are attached to the walls in specific locations. These thermocouples relay temperatures to a computer, which tracks temperatures during the test. As the stove operates, temperatures are tracked. The stove is fired as hot as possible using oven dried softwood strips which are stapled together to create a “firebrand” which burns much hotter and faster than cord wood.

The benchmark temperature, which determines safe clearances, is typically 115 degrees F over the ambient room temperature. In other words, if the ambient room temperature is 70F, the benchmark wall temperature cannot exceed 185F. If temperatures exceed 185F, the stove must be located further away from the wall. That is why movable walls on tracks are used. If the temperatures exceed 185F, the walls are moved back until the temperatures recorded are less than 185F. In a nutshell, the stove is run through the complete test, the temperatures are recorded, and safe clearances are established.

How to Measure

If the listed clearance to a bare, unprotected wall is 36”, then you would measure in a straight line from the stove to the wall. The same goes for corner installations—-straight line to the wall. What part of the stove you begin your measurement depends on the brand stove. Some require that you measure from the top plate, some from the body of the stove. Check your owners guide for this information.

THE GOOD NEWS is that most current stove models are tested with reduced clearances…sometimes as close as 8”. Other models have optional read heat shields which reduce the wall clearance without requiring protection of the wall surface.

How To Protect the Wall

Ahh, the big question. First and foremost, check your owners guide to see what that manufacturer considers to be a protected or unprotected wall. To many, a protected wall is one where a non-combustible shield is placed a minimum of 1” away from the wall, and allows air to flow unimpeded from the bottom to the top. Non-combustible spacers are used to attach the shield to the wall. The most commonly used spacers are made of ceramic, sold at most retail shops and hardware stores.

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    Spacer Example (NFPA)

The shield can be constructed of sheet metal, copper, Wonderboard, cement board with tile attached, or masonry such as brick. The true key is to allow air to flow. This keeps the house wall cool, as the shield is a barrier to heat. The airflow behind the shield keeps the backside of the shield and the wall cool. The size of the shield required will depend on the stove.

Skeptical?  Think about why a car parked under a tree on a hot sunny day is much cooler than a car in the direct sun. The tree acts as a barrier, and the breeze pushes hot air away from the car. Or why folks put those cool looking window shades on the windshield of their car, and keep the windows cracked open——-the shade provides a barrier against straight line infrared heat, and the breeze flowing through the car keeps the inside of the car cool. Same set of physics when compared to a stove installation.

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   Wall Shield Top View (NFPA)

Some homes have an existing hearth area, where the brick is installed directly against a combustible wall. This is common for new homeowners who have recently moved in and found an existing hearth set up. While this looks nice, it may not satisfy the manufacturer of the stove you have or recently purchased. The National Fire Protection Agency (NFPA) states that this would give you a 33% clearance reduction. However, this is a general clearance and does not take into account the different design of the stove you have. Every stove is different. Go with what the manufacturer specifies because some believe that too much heat is transferred from the brick to the wall behind. The danger here is the inability to inspect the wall for heat damage. Unchecked heat over time will lower the materials ignition temperature to a point where potentially it becomes a real fire hazard. When in doubt, check it out! This may even mean removing the existing brick wall to thoroughly inspect.

Some products offer the ability to obtain dedicated rear stove shields to further reduce clearances. Some products actually have these shields as standard equipment. Check your owners guide to see if this option is available because in some cases, the stoves rear heat shield may be enough to protect the wall and give you the clearances you desire.

Chimney Connector (stove pipe)

Don’t forget to check the pipe clearances! Just because the stoves clearances can be reduced using a rear heat shield does not mean that the pipes clearances automatically fall into place. Check the clearance chart. Sometimes you can either shield the single wall chimney connector, or use a double-wall chimney connector for reduced clearances. Check the clearance chart for specific details.

What About Installing Older Stoves?

Accredited independent laboratories using the aforementioned test protocol did not test older stoves. For this reason, the NFPA (National Fire Protection Association) has provided generic clearances for these Non-UL stoves in their NFPA 211 Handbook. Most retail shops, chimney sweeps, and installer have this information. NFPA has their stove and fireplace standard 211, available at this link.
(see pages 211-39 and 211-40)

Here is one example of an NFPA wall reduction chart. Notice that stoves which were originally 36” form the wall can often be reduced to 12” (66% reduction).

What About Fireplace Installations?

Most stoves today have been tested specifically for a fireplace installation. The areas to focus are the mantel, top trim (under the mantel), and side trim. First, when it comes to this installation, check the specs. Review if theres a specific measurement of maximum mantel depth. Why? If the maximum depth is 10”, and your mantel is 13”, then the mantel could trap heat underneath. If the mantel traps heat, it will become hot itself and possibly overheat. The same goes for the top and side trim. If the depth exceeds the maximums quoted, you may need to shield those areas. Hopefully, that flexibility exists with your product.

My Wall or Mantel is Hot——Should I Be Concerned?

If you’ve installed the stove to the requirements, yet when you touch the wall or fireplace mantel, its hot to the touch. This does not mean that its unsafe. The human touch can safely handle temperatures of up to 135F. During the stove testing, if you remember that the threshold was roughly 185F——-thats a difference of 50F. If the stove is installed to requirements, you have nothing to worry about. If your fears persist, then you can shield the surface using a ventilated shield.

Summary:

While there are many more complex details involved in installing stoves because each installation is different, hopefully this article has given you an overview of whats involved, what to review, what to avoid, and what you should do.

Please install your stove safely, and don’t cut corners. Do exactly whats required, let your insurance company know whats going on, and have the installation inspected by a professional prior to starting the stove.

Follow these tips, and you won’t have to sleep with one eye open!


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