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Anatomy of a Firebox: Straight vs Angled

Straight-on vs Angled Fireboxes

Anatomy of a fireboxEver wonder why we ask what type of firebox design your zero clearance fireplace has? Does it really matter if have this information?

The answer is YES! Since the firebox is where all the magic happens, it is hands-down the most important part of your zero clearance fireplace system. The manner in which it is designed not only determines how much fuel is needed to create heat and how much of this heat is radiated into your living space, but also how your replacement fireplace door will fit in relationship to the firebox. Here at Fireplace Doors Online, we identify two types of firebox styles: Straight-on and Angled (also known as Traditional and Rumford, respectively). 

Straight-on (or Traditional) FireboxStraight-On Firebox

If you look at the construction of your firebox, you'll notice that the sidewalls have very little (if any) angle or splay. (Click on the Straight-On Firebox picture at the right for a larger view.)

The rear wall is flat and about the same width as your fireplace opening. This particular firebox style produces just enough heat for combustion and sends the remainder up to the chimney. It doesn't do much in the way of delivering an ample amount of heat into the room.

With the straight-on or traditional style, the fireplace door simply rests on the metal lip of the firebox for a "picture frame" look and is secured with the installation hardware that comes with the product. Depending on the manufacturer, fireplace doors will vary in how they are installed in your firebox and which tools they will require for establishing a perfect fit.

Angled Firebox

Angled FireboxThe angled firebox is tall and shallow. The rear wall is approximately one third the size of the fireplace opening, which gives the sidewalls their prominent angles. (Click on the Angled Firebox picture at the right for a larger view.)

Because the sidewalls are splayed, heat is radiated into the fire, as well as back into your living space. Some angled fireboxes have a slight hump towards the top of the rear wall, which helps to radiate even more heat. This produces a more efficient burn and reduces fuel waste.

When installing a replacement fireplace door on this type of firebox, the hardware that is included with the product, as well as additional mounting brackets, are needed. Some systems involve the use of alternative brackets, which fit the greatest number of zero clearance fireplaces. Alternative brackets can be used in place of or in combination with standard brackets to mount the fireplace door securely to the opening. This mounting system is used inside the fireplace opening anywhere a suitable surface is available and attached with self-drilling screws. 

Other systems consist of bottom wedge style brackets and top brackets with two right angles (which resemble an 'S' shape). These brackets are intended to fit in the space between the refractory material and the metal firebox and are used where there is no metal frame to attach the standard or alternative brackets.

If you still aren't sure about the anatomy of your firebox and need some assistance determining which replacement fireplace door is best for your zero clearance application, not to worry! We have Snapshot Quote to help! Simply fill out a small form and then send us the measurements and a picture or two of your fireplace, and we'll get back to you in just a couple of business days!


Last updated on August 27th 2019.