How to size a fireplace mantel? Commonly fireplace mantels are 6″ longer than each side of your fireplace, the depth is generally 7” to 12” and height 4” to 6”. The National Fire Protection Agency (NFPA) states that the fireplace mantel must be at least 6” away from the top of the fireplace box, “Where trim projects up to 1.5” from facing”, “Where trim projects more than 1.5” from facing” the trim must be 12” above the fireplace. If your mantel has trim sides they need to be 6” from the face on either side.

Fireplace Mantel Livingroom
Classic Masonry Fireplace with its mantel

Harmony in a room comes from the fireplace that’s in it, but the mantel above it is just as important to bring together that harmony, when you walk into any room with a fireplace your eyes are drawn directly to it and if the mantel is proportioned properly for your fireplace it can make it spectacular, and if it’s not well you know it’s going to be less then spectacular and probably look a little strange, so measuring properly is important.

So there is no specific size written in stone that a mantel needs to be, but you do need to take into consideration a few important design and proportion factors that will help you choose the right one, some of those factors are the size of your fireplace, the size of your room, does it fit in with your decor.

Also, the design of your home and what you as a homeowner want is very important when choosing a mantel, for example, are you going for a rustic cabin style, a modern look, minimalist or contemporary well whatever your style is there is a mantel for everyone.

With that said there are only a few small guidelines and sizing you do need to follow with your local buildings codes and these refer to clearances to combustibles which are about fire safety, in this post, we will talk about those requirements so you install your new mantel properly.

So please continue reading and allow me to guide you on the right path on how to size a fireplace mantel and give your fireplace that wow factor it deserves, and make it a beautiful focal point in your room.

How to size a fireplace mantel? Hight, Depth and Width.

Let us jump right into it and help you decide what size mantel will be right for you, and how to size a fireplace mantel

How to size a fireplace mantel width

So how long is your fireplace mantel width? are you thinking of changing it for something different? Do you look at it and wish it was just a little longer or shorter? or maybe you installing a new fireplace and haven’t decided what mantel you want yet.

Well to give you an example of how most mantels are sized, generally, you buy a mantel that is 12” longer than your fireplace, that would be 6” longer on each side so if your fireplace is 44” wide your mantel needs to be 56” or if your fireplace is 52” wide your mantel should be 64” wide.

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How to size a fireplace mantel, Depth and Height

The depth is generally 7” to 12” but can be shorter and the height can be 4” to 6”.

Now, remember these are just standard sizes, and like I mentioned before it’s not written in stone, but they do give you a good idea of where to start.

If you decide to buy or make a storage mantel which is a fireplace mantel that opens on the front and has almost like a hidden compartment inside, this has become a very popular style of the mantel and when buying one it’s good to consider what you would like to store in it and then decide how big or deep and wide you would like it to be.

Something else to remember you will need to take into consideration one important part of sizing your fireplace mantel, and that is to make it code compliant, and this is more about the positioning of the mantel than its size, so let’s jump into the fire codes and positioning.

Fire codes for installing a fireplace mantel

So let’s talk about fire codes and how they will dictate where you can put your mantel, now you might be thinking I don’t want anyone to tell me where I can install my new mantel, or maybe you are thinking that mantel has been there forever “I’m not about to change it or move it now”.

Remember fire codes are put in place to protect you and your family from a possible fire that can cause damages to your home and or something worse your house could catch fire.

Something else to remember is that most insurance companies won’t give you home coverage if these codes or measurements aren’t followed correctly.

Fireplace mantel clearances to combustibles

So when we ask the question about how to size a fireplace mantel? There are two types of open fireplaces, the first one that we will mention is the “Masonry fireplace” which is made of bricks and mortar, and the second the “factory-built or zero clearance fireplace”

Masonry Fireplace mantel installation

Fire codes on how to size a fireplace mantel

Something else I want to talk about is how to size a fireplace mantel on a Masonry Fireplace.

In the United States the National Fire Protection Agency (NFPA) state that the fireplace mantel must be at least 6” away from the top of the fireplace box on the top “Where trim projects up to 1.5” from  facing”

“Where trim projects more than 1.5” from facing” the trim must be 12” above the fireplace.

If your mantel has trim sides they need to be 6” from the face on either side.

These measurements as stated above are the same standard in Canada according to the (Wood Energy technical training W.E.T.T.)

The W.E.T.T. manual also states that “Metal like a damper control mechanism shall have not less than a 50 mm clearance from any combustible material on the face of the fireplace where such metal penetrates through the face of the fireplace”.

Fire codes on how to size a fireplace mantel

With these measurements, you should be ready to install a fireplace mantel and have the peace of mind that it is installed to code

Hot temperatures can cause Pyrolysis

Most people have never heard of something called “Wood Pyrolysis“, this is what happens when the wood is exposed to relatively low levels of heat over a long period of time, and this causes Wood or other combustible materials to undergo Pyrolysis, which causes chemical changes to occur, and the ignition temperature of the material falls and the risk that it can catch fire increases so the measurements below are for your safety and should never be overlooked.

Ooni Karu

Field reports have shown that if the wood is exposed to temperatures as low as 120 degrees celsius will begin to char and can cause spontaneous combustion, igniting over time.

A maximum of 90 degrees celsius is considered a safe amount of heat over a long period of time.

Pyrolysis is something common in fireplace mantels that are placed too close to a fireplace opening and that is one of the reasons why the safety standards below are put in place.

Factory-built fireplace mantel installation

Factory Built fireplace with a wood beam mantel

It is important to also talk about how to size a fireplace mantel for a factory-built or zero clearance fireplace.

So If you have what is called a “zero clearance fireplace” or also known as a “factory-built fireplace” this is a fireplace that has a metal box and is recessed in a wall or a chase.

Now if you own a factory build fireplace you should also look at the guidelines in your owner’s manual about clearances to combustibles and there should be a detailed guide that gives you a clear idea about these measurements if you don’t have the owner’s manual you can probably find it online.

If you have any trouble finding the make or model of your fireplace you will need to look for the certification label, this label is generally made of metal and hidden behind a top, bottom, or side panel and is black in color with silver or gold lettering.

Your fireplace should have details on it about clearances to combustibles, for example, its certification could be ULC or CSA among others and you will also see the year it was manufactured along with its serial number or model number, and the name of the manufacturer this label is very important to keep on or close to your appliance and should never be put in the garbage misplaced.

The certification label dictates whether the wood-burning appliance is certified and can be an obstacle to getting home insurance if misplaced.

If you don’t have the manual then it can always be found online at the manufacturer’s website, the label with its serial number or model number will help you find exactly what you are looking for.

Fireplace Mantel Design Ideas

There are so many design ideas out there that it would be hard to talk about all of them in this post but I do want to leave you with a few ideas that are trending now, faux concrete mantels are becoming popular because they give you a modern look if you are looking for a drastic makeover.

Also one of my personal favorites is a storage mantel that has a secret compartment that folds down on the front or slades out on each side, giving you the versatility of storage space, and many people like this idea for tucking away candles, etc.

In an upcoming post, I’ll try and touch on design a little deeper.


I hope this post on how to size a fireplace mantel was useful and that it helps you choose the right fireplace mantel and install it safely and properly, thank you for reading and if you would like to receive more wood burning tips and product reviews please sign up for my email newsletter, have a wonderful day.

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