Wood-burning stoves easily reach temperatures over 900°F. Without sufficient distance between the stove and nearby walls, and a heat shield, heat will penetrate the building and increase the risk of fire and structural failure.
Most people stumble on heat shields as a solution to reduce the distance between the stove and nearby walls. Heat shields allow stoves to sit closer to walls, preserving space while meeting fire/temp regulations.
However, whether you need a heat shield depends on the distance between your stove and combustible and exposed materials.
This guide explores what to put behind a wood-burning stove, with advice on clearances, heat shields, and sizing.
Why Clearances are So Important to Get Right
Clearances are essential because they determine the level of heat transfer between the stove and nearby surfaces.
By increasing the clearance, you reduce the temperature at the wall and push the stove out, which requires more space.
Wood-burning stoves reach temperatures that can easily ignite combustible materials – a heat shield protects these materials, much like the heat shield on a shuttlecraft protects it from atmospheric entry (albeit not as extreme).
Even if materials don't ignite, they can break down under prolonged exposure to high temperatures. They can also become susceptible to combustion at lower temperatures due to pyrolysis.
The bottom line - every stove installation requires a safe clearance from combustible materials.
Reducing the clearance without a heat shield substantially increases the fire risk and can be illegal, as set out by National Fire Protection Association (NFPA) codes.
The NFPA notes that reduced clearances are acceptable with the following:
*Such as heat shields. When a heat shield is specified, the clearance can be reduced in line with guidelines set out by regulations.
Benefits of Installing a Heat Shield for a Wood Stove
Benefit # 1 - Safety
While many stoves have insulation blocks in the back and sides to minimize heat loss, an external heat shield substantially increases safety still.
Even a thin metal or enamel heat shield is effective, spreading lots of heat over a large surface area to reduce the surface temperature. An air gap also prevents heat on the shield from transmitting to the wall behind.
Heat shields protect combustible materials and reduce heat transfer into the wall, helping preserve plaster, stone, and brick and mortar.
Benefit #2 – Close the gap
If an 18" gap from the back of the stove to the wall is too much, you can use a heat shield to close the gap significantly.
For example, the NFPA recommends that a stovepipe be at least 18" from the nearest combustible material. However, with an air-cooled heat shield attached to the wall, that distance drops to 6", closing the gap by 12".
Benefit #3 - Compliance
Building codes set out by the NFPA (as well as local codes) stipulate the minimum distances between a stove and its surroundings.
Staying on the right side of compliance is critical to assure the quality and safety of your installation. The last thing you want is an unsafe stove, and additionally, it provides complete peace of mind if your installation requires inspection.
Benefit #4 – Aesthetics
Heat shields come in a wide range of finishes and colors and help to cover up unsightly building work and uneven surfaces.
Vitreous enamel is the most common material with a smooth black or white surface, or you can get brick or stone-effect enamel.
One of our favorite options is crackle glaze enamel in duck egg blue or ochre yellow, which gives any stove a classy, understated appearance.
The Different Types of Heat Shield
Heat shields come in various materials, from thin metal sheeting to thick brick.
Here are the main types of heat shields in use today:
Masonry
Brick and stone are perfect heat shields with a minimum 1" air gap. The materials are cheap, and you can build the shield yourself.
Another option is a cement board separated from the wall by one-inch ceramic spaces – you can then dress the board with ceramic wall tiles.
Sheet metal
Sheet metal works brilliantly as a heat shield with a minimum of 28 gauge. Thicker is better, but you don't need anything over 24 gauge.
As with masonry, you need a 1" gap between the sheet metal and the wall. Ceramic or stainless-steel spaces are your best options.
Vitreous enamel
Vitreous enamel heat shields are decorative items that perform similarly to sheet metal without the industrial, raw looks.
Some enamel heat shields have a convection system that radiates heat back into the room, further reducing temperature penetration.
Note that all heat shields should be affixed to the wall using non-combustible fixings with an air gap of at least 1". If you fix the heat shield directly to the wall, you will only transfer heat between the two elements.
Important Note on Clearances and Materials
There is no material or heat shield on the market without insulation or an air gap that provides approved clearance reduction.
This means that sheet metal, enamel, tiles, or anything else attached directly to the wall with no air gap cannot be classed as heat shields.
Always follow the NFPA-211 guidelines for heat shields. Recommended clearances for specific wood stoves will be detailed in the instructions.
Failure to do so could put you and everyone else in your household in danger.
How Clearances for Wood Stoves Are Calculated
Firstly, clearances are calculated in all directions from a straight line, meaning the stove's top, bottom, and sides are included in calculations (although the flue sorts the top). This ensures the stove is never too close to a combustible surface.
Clearances are calculated based on no heat shield first and adapted to suit when a heat shield is specified. For example, the NFPA recommends an 18" clearance from the back of the stove.
With a heat shield, the 18" back of the stove clearance reduces to 6". If the heat shield stands out by 1" (with an air gap), the clearance is 5".
While it is acceptable to increase the gap, reducing it below recommended clearances is a fire safety risk and should be avoided.
Wood Stove Clearances
The industry standards for wood stove clearances are stipulated in NFPA-211.
For example, it says that unlisted (not listed by the Underwriters Laboratory) stoves "shall be not less than 36 inches above and around all sides, and with adequate legs and floor protection."
The clearances are smaller for stoves that are listed:
Clearances Without Shielding
With Air-Cooled Wall Shielding:
This works out at a 2/3 reduction.
If you put an air-cooled heat shield on the stove/pipe, the figures become:
This works out to a ½ reduction. The same also applies to an insulated heat shield.
Masonry Heat Shields:
This works out to be a 1/3 reduction.
As we can see, the most significant clearance reduction is with air-cooled wall shielding, thanks to greater heat protection.
Important Note on Clearances in Residential Buildings
If you live in a residential building, you are probably subject to building codes.
Your stove manufacturer might provide recommendations for distances, but the UL does not list most tiny stoves, so the local building code comes into play.
Most tiny stoves are unlisted, so they have minimum distances of 36" around all sides.
Unlisted stoves must adhere to clearances specified in NFPA 211, but a heat shield usually allows a 2/3 reduction providing it is air-cooled.
Seek the advice of an expert before buying and committing to installation so that you know what's what.
What Size Does a Heat Shield Need to Be?
The ideal size for a heat shield is relative to your stove. It should be 2-3" larger in all dimensions, although it can be wider and taller to suit the space. It's also good practice to size up the closer the stove is to the wall.
The best heat shields have an air gap. They are effective because air circulating behind the shield whips heat away from it, keeping the material behind at a low temperature. One way to ensure airflow is to leave the shield open or the top and sides open.
If you have a masonry heat shield, size doesn't matter because it will probably eat all the space behind your stove. Most tiny stoves use a sheet metal or enamel heat shield, which is best when it is 2-3" larger than the stove.
Regarding thickness, 28-gauge is the minimum for sheet metal, and 24mm for enamel – you can make this thicker if you want more cooling power.
