Heat Shields for Clearance Reduction
In addition to using proper materials, adequate clearances are the most important safety feature of any wood stove installation. A properly installed and maintained wood stove can be one of the safest appliances in your home. But cheating on clearances can create a very dangerous situation.
Wood stove clearances cannot be eliminated entirely, but they can be reduced significantly by using a properly constructed heat shield. It's critical that heat shields are designed properly, and that rated clearance reductions for the type of shield are followed.
NFPA-211, the industry standard for wood stove installations, describes three different types of heat shields. (Note: NFPA-302 is the standard for boats, which is a bit different from the rules outlined in NFPA-211 and this article. The rules in NFPA-302 are less detailed than NFPA-211, so we suggest following NFPA-211 standards unless you're installing on a boat.)
Dwarf Stove Clearance Requirements
Distances to Combustibles Without Shielding
- 18” from back of the stove
- 16” from sides of the stove
- 18” from single-wall pipe
- 2" from insulated pipe
Distances to Combustibles With an Air-Cooled Heat Shield on the wall (2/3 reduction)
- 6” from back of stove
- 5.33” from sides of stove
- 6” from single-wall pipe
- Read about building an air-cooled heat shield
Distances to Combustibles with an Air-Cooled Heat Shield Attached to Stove/Pipe (1/2 reduction)
- 9” from back of stove
- 8” from sides of stove
- 9” from single-wall pipe
- Read about building an attached heat shield
Distances to Combustibles with an Insulated Heat Shield (1/2 reduction)
- 9” from back of stove
- 8” from sides of stove
- 9” from single-wall pipe
- Read about building an insulated heat shield
Distance to Combustibles with a Masonry Heat Shield (1/3 reduction)
- 12” from back of stove
- 10.66” from sides of stove
- 12” from single-wall pipe
- Read about building a masonry heat shield
Don't Forget the Pipe!
Both the stove and the stovepipe have their own required clearances that must be observed. In most cases, you'll need to build a heat shield for both your stove and your pipe to safely achieve your desired clearance reduction.
How to Calculate Clearances with a Heat Shield
Clearances are calculated from the heat source to the combustible surface. So an 18" clearance reduced to 6" with a shield that stands 1" away from the wall would be at least 5" from the shield to the heat source.
How Big Should Heat Shields Be?
Clearances are calculated in all directions in a straight line. The easiest way to figure out what surfaces a shield needs to cover is to cut a dowel to the rated clearance you're testing.
For example, from the back of the Dwarf stove, the rated clearance is 18" to combustibles. With an 18" dowel, measure all points on the wall that you can touch with one end of the dowel, while the other end is touching the back of the stove. All those points must be covered by the heat shield.
Do the same for the stovepipe and the sides of the stove at their respective clearances.
You'll note a couple of things on this exercise. First, the heat shields will tend to be significantly larger than the profile of the stove or stovepipe. Second, the further away the stove or stovepipe is from the combustible material, the smaller the heat shield needs to be.
Don't Trust Pictures
We get a lot of questions about photos of stoves that appear to have much closer clearances than allowed. "How are they able to do that?"
Sometimes it can be hard to tell how close a stove is to a wall from a photo. Clearances may be OK, but appear in a photo to be closer than they actually are.
People do frequently violate clearances and post the results online. Just because someone did it doesn't mean it's safe.
In some cases, stoves are "staged" in a way that they could not be installed, and then corrected later. For instance, on Tiny House Nation S5E15, they didn't have time to install the flue system before filming the episode, so the set dressers just put the stove where they thought it looked best. Photos on the episode show the stove way too close to the wall, but if you look closely, you'll see that the stove was not hooked up yet.
Pyrolysis - Why Clearances are So Large
Clearances are important because wood stoves get very hot while in operation. Combustible materials that are too close to the stove can heat up past their autoignition temperature, and catch fire. A spark is not required to start a fire, just heat, fuel, and oxygen.
In most cases, clearance violations will not cause a fire immediately. As material is repeatedly heated, it deteriorates on a molecular level and its autoignition temperature begins to drop in a process is called pyrolysis. After months or years of repeated heating, a surface that "hadn't had a problem yet" can spontaneously burst into flames.
To be safe, exposed combustible materials around the stove should never exceed 117 degrees F over ambient temperature, and unexposed areas (under the hearth, for example) should never exceed 90 degrees F over ambient. If you observe potentially combustible materials around a stove discoloring, that can be an indication that pyrolysis is occurring. But you won't always be able to see it.
What Happens When you Cheat
Clearance violations are an especially dangerous problem because they often don't cause a fire immediately. Sometimes pyrolysis is visible as discoloration or charring on the surface of combustibles, but sometimes the pyrolysis can occur inside a wall. You could use your wood stove with no problems for months or years until one day, your wall catches fire from the inside without warning.
Cheating clearances can also be caused by using improper materials. For instance, if you use pellet pipe instead of proper Class A chimney pipe to penetrate your roof, and you follow the manufacturer's suggested clearance to combustibles, you'll create a dangerous clearance violation. Pellet pipe is rated for much lower temperatures that wood stoves produce, so the clearances are calculated assuming those lower temperatures. Connect pellet pipe to a wood stove, and the manufacturer's rated clearances are no longer adequate. Not to mention pellet pipe is very toxic when heated to wood stove temperatures.
Note for Residential Spaces
Spaces that are subject to building codes generally have specific requirements for clearances. If a stove is UL listed for residential spaces, you need to follow the manufacturer's instructions in the manual. However, most tiny stoves are not UL listed, so you may need to follow the local building code's guidelines for unlisted stoves, which typically require 36" clearances to combustibles in all directions.
If you are using a heat shield to reduce clearances in a project subject to building codes, the shield cannot reduce clearances from the appliance to the wall less than 12" with an air-cooled shield or less than 18" with an insulated shield unless the shield and stove are specifically tested and listed for that purpose. Connector clearance can be reduced to no less than 6" with an air-cooled shield or 9" with an insulated shield.
How to Construct Air-Cooled Heat Shields
By far the most effective heat shields are the air-cooled type. These shields are constructed with a sheet of 24 gauge or thicker sheet metal, or 1/2" or thicker cement board, with 1" of air space behind the shield and around the perimeter to allow free airflow. 1" heat shield spacers are available for this purpose.
Try to avoid placing a spacer directly between the center of the stove and the wall, since spacers can conduct heat through the shield to the combustible wall. It's usually best to place the spacers around the perimeter of the shield.
The airflow behind the shield is critical for its success. As the shield is heated, the natural convection of air passing behind the shield will keep the shield and the material behind it cool. Enough of the perimeter of the shield must be left open to allow air to enter the bottom of the shield and exit the top. Acceptable airflow strategies are:
- Leave all four sides of the shield fully open.
- Close out the left and right sides of a shield, but leave the entire top and bottom open to allow air to enter the bottom and exit the top.
- If the shield is installed on a flat wall (i.e. not around a corner), you can close out the bottom of the shield if you leave both sides and the top fully open. Air will enter the bottom at the sides and exit the top and sides. This design can't be used if the shield goes around a corner.
A proper air-cooled heat shield reduces single wall pipe clearances by up to 2/3 (18" becomes 6") when used as a wall protector, or up to 1/2 (18" becomes 9") when used as a ceiling protector.
Air Cooled Shields Attached to the Stove or Stovepipe
The industry standard NFPA-211 guidelines for wall and ceiling shields does not cover attaching shields directly to the stove or pipe, but it is often possible to reduce clearances with attached shields in some situations.
Attaching air-cooled heat shields directly to the body of Dwarf stoves using our factory heat shield kit cuts required clearances in half, so 16" from the sides becomes 8", and 18" from the back becomes 9". Similarly, attaching air-cooled heat shields to our single-wall pipe creates a double-wall pipe, which requires 9" clearance to combustibles with the heat shield in between instead of the standard 18".
Keep in mind that adding a shield to the stove itself will only reduce clearances for the stove. In most cases, you'll also need to add a heat shield for your stovepipe.
The easiest way to make air-cooled heat shields for stovepipe is to cut a piece of single-wall stovepipe lengthwise that is 1" larger than the stove's pipe (e.g., a stove with 4" pipe would use 5" pipe as a shield). Then, screw the shield to the pipe using 1-1/4" heat-proof screws and 1" ceramic or metal heat shield spacers. You can also slip the entire shield pipe around the stovepipe and use screws and spacers to attach it.
Check out Nick's 5er installation video for an example of using shields attached directly to the stove and to the pipe to reduce clearances with minimal visual impact.
If your stove is produced by a different manufacturer, attaching a DIY shield directly to the stove or stovepipe may not be permitted, and factory heat shields may or may not be available. So be sure to check with the manufacturer.
Insulated Heat Shields
Insulated heat shields are rarely used for small space installations because they require additional material, and are less effective. Insulated shields are identical in appearance and construction to air-cooled shields, but instead of 1" of air space behind the shield, you use 1" of fireproof insulation like rockwool or ceramic fiber. A shield of this type can reduce wall clearances by 1/2 or ceiling clearances by 1/3.
Masonry Heat Shields
Masonry shields offer a classic "fireplace" look but are less commonly used for tiny living applications because they are no easier to construct than air-cooled shields, are heavy, and they are less effective. Masonry heat shields are essentially a standard brick wall, which uses 3-1/2" thick masonry blocks with no air space. Shields of this type can reduce wall clearances by up to 1/3, and are not generally used for a ceiling.
Shields That Are Not Shields
Tile attached directly to the wall with no insulation or air space is not a heat shield. Tile will conduct heat directly through to the combustible surface behind it. Unless it's at least 3-1/2" thick, a layer of tile provides no rated clearance reduction.
Sheet metal attached directly to the wall with no air space will also conduct heat straight through it, and provides no rated clearance reduction.
Any shield type other than the three types mentioned in NFPA-211 should generally not be used for clearance reduction unless that configuration has been tested. While shields with an amount of air space or insulation other than 1" or shields with a double-layer of sheet metal would likely provide some benefit, the amount of safe clearance reduction they would provide is unknown.
It should also be noted that no testing has been conducted on how effective using multiple shields is. While combining an air-cooled wall mounted heat shield and stove mounted shield is tempting to reduce clearances further, we strongly recommend not furthering reductions beyond what the wall-mounted shield will allow (2/3 reduction).
Want to run your ideas by an expert? Or check to make sure your plan meets the clearance requirements for a safe wood stove installation? Contact us at firstname.lastname@example.org and we will be happy to offer advice and help you plan.
68 thoughts on “How to build heat shields for wood stoves”
Is Aluminum ok for a heat sheild in a sauna?
Good question. NFPA-211 only specifies “24 gauge sheet metal” for wall protectors. It doesn’t specify the type of metal. I’m using 0.032″ 2024-T3 alclad aluminum for my wall heat shield in my Airstream, and the shield hardly gets warm when the stove is burning. I don’t expect 24 gauge or thicker aluminum sheet would be a problem for air-cooled heat shields attached to the wall or ceiling. Aluminum certainly has the advantage of being rust-resistant in a sauna environment.
For heat shields attached directly to the stove body or stovepipe, I’d suggest opting for stainless steel or carbon steel instead. Aluminum has a melting point of around 1,200 degrees F. That’s roughly the temperature you’d expect from a chimney fire, so there’s a chance it could fail and allow the fire to spread to the structure. Steel, with a melting point in the 2,500 to 2,800 degree F range, would be less likely to fail during a chimney fire than aluminum.
can I use metal roof siding for heat protector?
Yes, as long as the sheet metal is 24 gauge or thicker and isn’t covered by a combustible coating, you can use it to build a heat shield.
What is the size and thread pitch of the bolts used to mount a heat shield directly to the Stove with the factory bolt holes?
The vast majority of the bolts on the Dwarf Stove, including the accessory mounting points, are threaded M6 1.0. The factory screws are pretty short since they’re mostly there to plug up the holes when you’re not using them. If you’re making a DIY heat shield, I suggest using 1-1/4″ long stainless machine screws with 1″ ceramic or steel heat shield spacers between the sheet metal and the stove. If you want to paint the screw heads and the shield to match the stove, use Stove Bright Flat Black.
Are there any specification requirements for the Rockwool for the no airspace alternative? Does Rockwool 60, 1 inch thick, work?
NFPA-211 specifies “1 in. glass fiber or mineral wool batts.” 1″ thick Rockwool is perfect.
Hi Dan. It has been a while, but I did install 1 inch Rockwool with a 1/2 cement board. I have a question about NFPA 211. It says the minimum clearance from the wall using this method is 18″, but then on the bottom gives the formula to calculate the minimum allowable clearance – Required clearance (1-R/100)
If the wood stove requires 23″ clearance will my wall allow for 11.5″ side clearance, or is 18″ the minimum? Thanks for helping me clarify!
For a code-compliant installation, the minimum clearance is the limit to how close you can get unless the stove manufacturer specifies otherwise. So, if your calculated clearance (using the formula) is less than 18″ in this case, then the minimum clearance your inspector will likely want to see is 18″.
For clearance above the stove, can any metal with 1″ air space work?
My design puts the stove 5″ closer to the ceiling than recommended and I’m trying to figure out the best way to deal with it.
NFPA-211 specifies 24 gauge or thicker sheet metal. It doesn’t specify the type of sheet metal. You want something solid (no perforated sheets), and non-combustible (not plastic coated or paint other than high-temp paint). For an air-cooled shield attached to the ceiling, stainless or carbon steel, or even copper, aluminum or galvanized steel should be fine. I wouldn’t use aluminum or galvanized steel in contact with the stove or flue system (due to the lower melting points of aluminum and zinc), but attached to a wall or ceiling shouldn’t be a problem.
Thanks for this information. It’s super helpful. I know that there needs to be an air gap of at least an inch below the heatshields (as well as behind and around). Quick question though, can it be higher than an inch off the ground? My stove has 6″ legs, and I’m curious if I could raise the bottom of my heatshield up to 3″. Thanks!
That shouldn’t be a problem as long as it doesn’t expose any combustible material within the standard clearances of the stove.
i get the 18 ” clearance from all points of the stove itself, but i dont see any clearances mentioned for the stove pipe. do i have to run the heat shield all the way up?
Yes, you need to take into account the clearances for both the stove and the stovepipe when you’re designing your installation. Different stoves and different pipes require different clearances, so you’ll need to consult the manufacturer’s specs. The Dwarf, for instance, requires 18″ clearance from the back and 16″ from the sides. Our single-wall stovepipe requires 18″ clearance to combustibles in all directions, and our insulated pipe requires 2″ clearance.
Whether you need to run the shield all the way up the wall or not will depend on the details of your specific installation. Typically, if you need shielding around the stove, you’ll probably also need similar shielding around any single-wall pipe. If you’re not sure about exactly what you need to do or what your options are, shoot us an email with some pictures or drawings to email@example.com and we’ll be happy to help.
Can you layer heat shields, as long as there’s at least an inch of space around each successive layer? For instance, use the heat shield that is sold for the dwarf 3k, then 2″ away set up another heat shield with 2 inches of space behind it? This is for a tiny home/mobile application, and I would prefer to avoid the weight of a masonry surround, if I can help it.
That’s a great question. Can you install a second heat shield around your wood stove to reduce clearances even further?
Intuitively, it seems like it would work. If one shield provides 1/2 or 2/3 reduction, wouldn’t a second additional shield provide an additional 1/2 or 2/3 reduction? Unfortunately, the reality is more complex than that. A second shield would likely provide some benefit, but it’s impossible to know what the actual minimum safe distance from combustibles would be without testing the assembly.
Since the clearances around your wood stove are what keep your home and family safe, we recommend sticking to industry-standard clearance reduction methods. If you were to use air-cooled wall shields (2/3 reduction) along with the Dwarf Heat Shield Kit (1/2 reduction), our clearance recommendation would be no more than the 2/3 reduction allowed by the more effective of the two shields.
Since you mentioned a masonry surround, it’s worth noting that covering the walls around your stove in masonry is not required, and does not provide any inherent benefit. Outside of the required clearances to combustibles, your surround can be wood, drywall, or whatever material you’re using for the rest of the room. Simply covering the surrounding material with tile does not provide any rated clearance reduction unless the tile is at least 3-1/2″ thick (a standard brick wall), and then only 1/3 reduction.
Many professionally installed tile surrounds are actually part of an air-cooled or insulated heat shield, built according to the guidelines of NFPA-211. They’re often installed seamlessly enough to provide the appearance of a simple tiled wall, but they either incorporate 1″ of fireproof insulation or 1″ of air space between the backer board and the wall.
Thanks for the response
What about floor protection? I’ve built a hearth recently that is stainless steel sheeting, over top of 2 layered 1/2 inch sheets of micore 300 (mineral fiber board) which is then mounted on wood. Is that sufficient to protect the wood?
Jessica- Good question. Floor protection (hearth design) is a bit different from wall/ceiling protection. The stove tends to be closer to the floor than the walls/ceiling, and the amount of heat radiating or conducting through the bottom of the stove can vary quite a bit depending on the design.
It would be best to check your wood stove’s manual to find the manufacturer’s instructions for building a hearth for that particular model. The hearth design you mentioned would be acceptable for our Dwarf Stove, but might not be acceptable for another model wood stove.
Absent guidance from the manufacturer (or for unlisted stoves), NFPA-211 has some general guidelines for safe installation. This guidance is probably overly conservative for most wood stove models, so seeking out the manufacturer’s requirements is worthwhile if they’re available. The guidance varies depending on how much ventilated air space is below the stove. Stoves with taller legs and ventilated stands require less protection than those with shorter legs/stands or no legs.
See NFPA-211 section 184.108.40.206 or consult with your installer. The requirements vary from 2″ solid masonry with sheet metal on top for stoves with 6″ legs or ventilated stands, to 4″ hollow masonry with internal air flow and sheet metal on top for stoves with 2″ legs or ventilated stands, to requiring a fully non-combustible floor (gravel, concrete, or earth with nothing combustible on the underside) for stoves with legs shorter than 2″.
Hello, I’ve read your recommendations for clearances, including the installation of heat shields. But, I don’t see your recommendations for the floor under your Dwarf 3kw. I do see the 18″ dimension, but I don’t see your recommendations for the floor itself. I would like to place your heater over the steel floor of a bus.
Thank you. R.B.
Check out the Dwarf Stove Manual for installation requirements. Hearth design starts on page 12 of the current version. If you have a combustible surface like plywood subfloor under the stove with the standard legs, you’ll need a minimum 1/2″ thick non-combustible material covering the floor, extending 12″ in front of the stove, and matching the clearances to the sides and back. That can be 1/2″ cement board plus sheet metal on top, or 1/4″ cement board with 1/4″ tile on top. Thicker is always acceptable. If you’re using the wood storage stand or tall legs, you just need ember protection under the stove.
If your floor is solid steel and there’s nothing combustible anywhere under the stove, including on the other side of the steel, then you could put your stove directly on the bare floor if you wanted. Most people would build some sort of hearth for aesthetics, but there are no strict requirements for hearth thickness if it’s not protecting anything combustible.
Since we are including the “wood storage stand” and 4” legs. Does that change how we treat the floor regarding a combustible surface. Is concrete board/tile still needed?
Yes, if you’re using the Dwarf wood storage stand and/or the tall legs, that reduces the thickness required for the hearth. In that case, you don’t need the 1/2″ thick noncombustible material, only ember protection. 24 gauge sheet metal or similar material under and in front of the stove would be sufficient. See the Hearth section of the Dwarf Manual for info.
Hi Dan! First off, thanks for being such a wonderful resource! I just bought a home with a WETT certified wood stove in Canada, which reassures me it has been installed safely. It has a large heat shield silver coloured metal heat shield which although functional, it quite an eyesore as it looks pretty industrial! I am wondering if it would be safe to either paint the heat shield black with high heat paint, or clad it with decorative tin ceiling tiles (white or black). Thoughts on whether this would compromise the safety/protection provided by the heat shield? Thank you!
While I’d defer to the manufacturer’s instructions, local codes, and the judgment of your WETT inspector for a final decision, in general, there’s nothing in the NFPA-211 guidelines that would prevent you from painting a sheet metal shield with high-temp paint or making the sheet metal thicker by adding decorative tin to the face of the shield. As long as you’re not adding anything combustible to the shield or blocking the air space around/behind the shield, you wouldn’t be changing the type or performance of the shield by doing so.
Awesome thanks Dan! And what about adding metal ceiling tiles as a “cladding” to the heat shield? That’d be my preference, aesthetically, and I’ve seen it online BUT per your post above.. you can’t trust the pictures!
Adding another layer of sheet metal on top of the existing metal shield material should simply have the effect of making the shield metal layer thicker. NFPA-211 requires the metal to be 24 gauge or thicker, so adding additional thickness to the face of the shield shouldn’t negatively impact the shield’s performance. Keep in mind that the tiles need to be entirely non-combustible, so make sure the tiles have no combustible coating and make sure they’re actually metal and not plastic or something else. If the existing shield has gaps around the edges, don’t obstruct them since the gaps are needed for airflow behind the shield.
If in doubt, you can always get a quick service call from your WETT inspector to verify your work is safe. The inspector will be familiar with local codes, which vary from place to place.
This is SO helpful! Thanks so much Dan! 🙂
My manufacturer says combustibles should be 400mm We have them at 225mm. If I placed a cementfire board 12mm onto that timber would this timber then become non combustable? Or would I need an air gap?
Good question. This is a very common point of confusion when calculating clearances to combustibles.
Per the NFPA-211 guidelines, simply covering the surface of a combustible material with a thin layer of non-combustible material provides no rated clearance reduction. The heat will conduct through the noncombustible material, and may heat the combustible material behind it to an unsafe temperature. The minimum thickness of the noncombustible layer needs to be at least 3-1/2″ thick (i.e. a standard brick wall) to provide a rated reduction with no air space or insulation in between.
In your case, you need at least a 44% reduction to get from 400mm to 225mm. So, the acceptable methods would be either (1) to use a 1″ layer of fireproof insulation behind either a 1/2″ (12.7 mm) layer of cement board or 24 gauge (0.61 mm) or thicker sheet metal for a 50% reduction, or (2) to use the same 1/2″ cement board or 24 gauge sheet metal with 1″ of air space behind and around the perimeter for a 66% reduction.
Note that both of the above clearance reductions are for a wall-mounted shield. Ceiling protectors are less effective than wall protectors, so the only option in this case would be the air-cooled shield for a 50% reduction to the ceiling.
Keep in mind that the National Fire Protection Association which publishes the NFPA-211 standard is a US-based organization. Since we’re talking metric, I’m guessing you’re outside of the US. While physics tends to work the same across the pond, building codes might not, so be sure to check with your local permit office before finalizing your plans.
What about painting the metal shield with HiTemp paint? The can I have says it’s good for 1200 degrees. Does that change anything about clearances – would I need to increase spacing if I do this?
Yes, you can absolutely paint your shield with high-temp paint without negatively impacting its performance. In fact, the factory coating applied directly to our Dwarf Stoves is Stove Bright brand high-temp paint. Keep in mind, though, that high-temp paint needs to be exposed to temperatures in the 600 degree F range to properly cure. A heat shield is unlikely to ever reach proper curing temperatures during normal use, so the finish will be less durable than if it’s cured properly.
If your painted shield is small enough to fit, you might be able to cure it in a household oven. You’ll need to ventilate the space pretty well since the paint will off-gas while it cures. Check the manufacturer’s instructions for curing, and your oven’s manual for its capabilities. Stove Bright requires 450 degrees for 60 minutes, and then 600 degrees for 45 minutes. 900 degrees F can damage the coating if applied in the first two burns, so the oven cleaning cycle is probably too hot for that purpose.
when putting a heat shield in a corner, should there be a 1″ gap between the two side pieces or can they butt up to each other in the corner
Good question. The side pieces should butt against one another in the corner so that there’s no line of sight past the shield to the corner.
Yes, you will still need to build a proper hearth underneath the stove. The Dwarf Heat Shield Kit reduces the required clearances to combustible walls around the stove, but does not affect the thickness of the hearth required to protect the floor. See the Dwarf Manual for detailed hearth requirements.
From the Q&A here, I am understanding that it’s required that you need 9″ clearance from the stove pipe to your heat shield, but you need 12″ all around the stove for having the required space for a proper hearth. Is it safe to conclude that the actual minimum inches you REALLY need is 12″ from your stove to the heat shield instead of saying 9″?
Good question. It’s going to depend on your type of installation and the manufacturer’s instructions.
If you are installing a stove in a residential building that has to comply with building codes, then you have to follow the instruction of the authority having jurisdiction (i.e. local code enforcement). Codes typically require no less than 12″ clearance in any direction with a proper heat shield unless both the stove and shield are UL listed to be used together for that purpose and the manufacturer allows the tighter clearances in their documentation.
If you’re installing a Dwarf stove in something like an RV or bus conversion, which would presumably not be subject to building codes, then you’re safe to follow the instructions in the Dwarf manual. We allow up to 2/3 clearance reduction around the rear and sides of the stove with a proper air-cooled heat shield attached to the walls that would otherwise violate clearances. In that case, the hearth just needs to match the clearances to the sides and back, so minimum of 6″ from the combustible wall to the back of the stove and 5-1/3″ to the sides, with the shield in between.
Excellent!! Thank you so much for clearing that up for me! I really appreciate all that you and your family does for the community of tiny living.
I’ve got access to some free stainless steel, formerly used as fridge freezer backing, that is 2mm thick.
I know the regulations say 24guage or thicker. 2mm is a lot thicker, is this ok? Can it be too thick?
Good question! The spec says 24 gauge or thicker and doesn’t establish an upper limit of thickness. 2mm is definitely fine. As far as an upper limit, since 1/2″ cement board is acceptable, it would follow that you’d be fine to use anything up to 1/2″ plate steel as long as you maintain the proper 1″ air space behind the shield.
Plate steel would be massive overkill for a simple wall shield, but we’ve seen a professional tiny house builder fabricate a wall mount for a Dwarf 4kW using 1/4″ plate steel as both the wall shield and the structural mounting plate. So, there are certainly applications for using thicker steel.
Thanks so much for this! That’s really helpful. My question mainly arose because I was trying to get some free metal for a community Facebook page and there’s some that is 2mm thick but nothing as thing as 24 guage!
Many thanks again, this site is amazing and has been very helpful for me to find the right stove for my 26ft Westerly Centaur!
Can I use 1/2″ cement board with a 1″ air space as a heat shield?
Yes, 1/2″ cement board with 1″ of air space behind it (and around the perimeter) is one of the approved heat shield configurations listed in NFPA-211. This type of air-cooled heat shield can reduce wall clearances by up to 2/3, or ceiling clearances by up to 1/2.
Great resource here. To clarify when you say there should be an inch space around the metal shield – we have a sheet rock wall and made the section behind the stove indented one inch with the hope that the heat shield could then be flush to the rest of the wall once installed On top of 1”ceramic spacers.
But you are saying the metal should not touch the rest of the wall, right? You’re saying that my piece of metal should be 1” smaller then the indent of the sheet rock wall on all sides?
Good question. The guidance from NFPA-211 for an air-cooled sheet metal shield requires that the air space behind the shield be ventilated. Specifically, the ventilation requirement is as follows:
So, generally, if you want to close out the two sides (but leave the top and bottom open), you can. If you want to close out the bottom and leave just the sides and top open, that’s acceptable only if the shield covers a single wall (does not cross a corner). And it’s always acceptable to leave all four sides open.
Ventilation is required because the convection of air behind the shield is what provides cooling. If you trap the air behind the shield, you’re essentially making an oven.
So, yes, if you want to use an air-cooled shield for maximum clearance reduction, will need to make the shield smaller than the recessed space you’ve built on at least two sides to allow 1″ of air space for air flow around the shield.
If you want to close out the entire perimeter of the shield for aesthetic reasons, that can be accomplished by using an insulated shield instead. Use 1″ thick glass fiber or mineral wool batts behind the shield instead of air space. This type of shield is not as effective as an air cooled shield, though, reducing clearances by only 50% as a wall protector or 33% as a ceiling protector.
Amazingly helpful. Thank you.
Hi, I am installing a small sauna stove in our newly constructed sauna. I have stud walls covered with foil bubble wrap and plan to use 28 gauge corrugated steel as a heat shield. I had originally planned to use 2 layers of 1/2” cement board with an inch gap between them. The outer surface was to be covered with troweled on vinyl cement patch. That option is not too attractive. I am thinking I will still have the first layer of cement board, 1 inch gap and then the steel. Do I need the cement board, or could I just use the steel over the foil bubble wrap? You do say above that the steel could be installed over whatever wall covering you are using for the room, which for this sauna will be cedar tongue and groove paneling. That implies paneling the space behind the stove and then installing the heat shield. In addition to proper heat shield I need to be aware of high humidity environment. I assume the first layer of cement board behind the steel is less likely to have mold issues than bubble wrap/steel or cedar/steel combinations.
Wood paneling, foil bubble wrap, or whatever other materials you’re using in construction are fine as long as they are outside of the stove’s rated clearance to combustibles. Technically, leaving the foil bubble wrap open behind the shield should be fine as far as the stove’s clearances are concerned. However, since bubble wrap is flexible and could intrude on the air space behind the shield over time, I’d suggest using a rigid wall material behind the shield to enforce that air space. Additionally, having unrestricted air movement against the insulation in the wall is generally not good practice. It’s up to your personal preference whether that rigid wall should be cement board, cedar paneling, something else.
Please also note that the ventilated metal shield thickness specified in NFPA-211 is 24 gauge or thicker. 28 gauge is too thin according to the guideline.
Thanks Dan, I’ll look for 24 gauge steel and use your heat shield spacier kit.
Since NFPA-211 only offers a limited number of materials and configurations to be used as heat shields, we can only recommend those specific configurations. An aluminum-faced fiberglass cloth should be non-combustible, but since it’s not one of the materials listed in the standard, we couldn’t recommend it as a material to use for any rated clearance reduction. If the shield is not necessary as you say, then adding noncombustible material in the manner you proposed wouldn’t do any harm. But it also wouldn’t reduce your rated clearances. If your installation is subject to building codes, it will be up to the local authority having jurisdiction (i.e. the inspector) whether the material would be acceptable in that area.
Ventilated metal heat shield thickness specified in NFPA-211 is 24 gauge for both appliance and connector clearance reduction. I have also seen 28 gauge referenced elsewhere online, but my 2019 copy of NFPA-211 says 0.024 in. (0.61 mm), 24 gauge on both Table 220.127.116.11 (connector clearance reduction) and Table 18.104.22.168 (appliance clearance reduction). 28 gauge is thinner, and therefore would generally not be acceptable according to the standard unless the manufacturer’s instructions of a UL-listed stove specified otherwise.
Hello! We want to install a woodstove in an alcove in our basement. Our ceiling is low so we will need a heat shield over the stove. How do we know how big the heat shield needs to be? Is there a distance beyond the outside of the stove that it needs to extend? (Meaning, if I drew a straight vertical line from the side of the stove to the ceiling, how far beyond that line does the shield need to go?
Good question! The easiest way to illustrate how big a heat shield needs to be is to cut a dowel to whatever the standard rated clearance is, and use that to measure. For instance, the Dwarf requires 18″ clearance to the back. Cut a dowel to 18″ long, and anywhere the dowel can touch the back of the stove with one end and the combustible wall with the other, there needs to be a heat shield in between.
For your stove, you’ll need to find out what the acceptable clearance from the top of the stove to the ceiling is. If there is no rated clearance from the top of the stove to the ceiling, then your safest bet is to use 36″. Cut a dowel to that length, and use that to mark the area of the ceiling that needs to be covered by the shield. Keep in mind that ceiling shields are less effective than wall shields, so 36″ clearance to the ceiling can be reduced to no less than 18″ with an air-cooled heat shield.
For an alcove installation, also keep in mind that some stove manufacturers have restrictions on the size of an alcove that their stoves can be installed in. Consult the manufacturer’s instructions to find out the requirements for your specific stove.
Hi! I am planning on installing a heat shield of 1/2” cement board with a 1” air gap using steel resilient channels as spacers. I am exploring alternative ways to finish off the front, stove-facing side that isn’t the traditional tile route. I was thinking about attaching Hardie Panel siding sheets to the cement board. These are 4’ x 10’ fiber cement panels that are factory painted and are 5/16” thick. I would leave at least 1” air gap at the top and bottom as requires and was thinking of screwing the siding panels through the cement board and into the resilient channel furring strips.
Do you think this would work? I like the idea of having a smooth painted finish that would look a little more modern. I’m not sure about the factory paint — I know that James Hardie advertises their siding products as noncombustible, but I haven’t been able to find any details about using them for this purpose. I appreciate your thoughts!
Thanks for the question! James Hardie siding products are indeed non-combustible (i.e. they won’t burn or contribute to a fire), so there shouldn’t be a problem with using them as part of a properly assembled wall-attached air-cooled heat shield assembly.
Good evening could I use 2 layers of 28 gauge corrugated steel to meet the thickness for the heat shield? Or use 1/2 in cement board and one layer of the 28 gauge also ?
One 1/2″ sheet of cement board with proper spacing and hidden by a 28 gauge sheet of metal attached to its surface would definitely be acceptable. Two layers of 28 gauge sheet metal wouldn’t strictly meet the standard, so while it would probably function, I’m not certain whether an inspector would approve it.
If you were going to use stone shields for a stove what would your recommendations be? I have seen stone surrounds for stoves that I really like. I am thinking of having stone around all but the front of the stove. It will be in a glamping tent. I am planning on a fresh air supply to the stove.
A stone shield would fall under the Masonry Heat Shield guidelines and would need to be 3-1/2″ thick to reduce wall clearances by up to 1/3. It would most likely be much easier to have either a stove or wall-mounted heat shield for a tent setup.
So I have a full T1200 Sierra wood stove going in. I got it for a decent priced and am going to get some use out of it until I upgrade. The problem is it’s an out the back wood stove. Because of a massive oak tree I am going through the roof. Without wanting to take up to much space. I was going to put in an air cooled heat shield up on top of cement board and bring my single wall in around 10”s away after the spacing. Would that be alright in Michigan? Down the road I’ll just elbow it when I get a top flue for more room for the wood stove.
You’ll want to check with your wood stove manufacturer’s recommendations for clearances but generally, wood stoves and single wall stove pipes need 18″ clearance from combustibles without a heat shield and 6″ with an air-cooled wall-mounted heat shield. So if your single wall pipe is 10″ from your air-cooled heat shield you will have more clearance than required which is always ok.
I know ceramic or slate tile is not thick enough to be a masonry heat shield but what if I used a tile with a 1 inch spacer behind it and open all sides?
Thanks for the question, Pat. Yes, you can build an air-cooled tile shield as you describe. You’d use 1″ metal or ceramic spacers to mount the tile backerboard to the wall, and then tile on top of it. Just be aware, the backerboard needs to be entirely non-combustible. You cannot use plywood backer for the tile if it’s used as a heat shield.
I have read through all the Q & A. It is simply amazing. I was hoping for information though about either buying a stand alone (maybe 2 to put together) heat shield or make my own out of smooth (not ruffled) 24 gauge metal. The stove guidline with its double wall dedign says stove in the corner, at 45 degrees, can be 7.5 inches away from the 2 walls. If placed straight in front of one wall, it states approved for 9 inches of space from back to the wall and 13 inches from side to a wall. Concerned about distance to windows with curtains on each wall. They will be 28 inches when measured from center of side to window. Can a shield be 2 to 3 inches away from the stove back and sides and 4 to 5 inches away from the walls?
Thanks for the question, Richard. 1″ of space behind an air-cooled shield is a minimum. More is acceptable. See this excerpt from NFPA-211.
Thank you so much for this helpful resource. After reading NFPA-211 I couldn’t find anything about electrical outlets and air-cooled heat shields. I plan to build a ventilated shield in the corner of my home where a wood stove will be installed and am wondering if I can leave a cut-out for access to an existing outlet. Or will I need to move that outlet to a new location before building the shield? Thanks and apologies if I missed this in the standard somewhere!
Thanks for the question, Jeremy. An electrical outlet would be a combustible material, so you wouldn’t be able to leave a cut-out for it if a heat shield was needed in that area. Aside from the outlet itself, you also wouldn’t want to create a situation where someone might leave a power cord plugged in, violating the stove’s clearances.