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I work for a company that makes glass for fireplaces and we often get questions from customers about whether glass bi-fold doors on a fireplace should remain open when the fire is going or should be closed. Is there a safety reason for one or the other? A performance reason?

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    Mike, I've made a major edit to your question to try to shape it up to be OK here - whether it's in scope for this site is up to the users. What happened is that your question was flagged by our system as potential spam and removed. While it's generally OK to link to a product, if it's not necessary to do so, it's generally better to avoid it. So I've removed the link to your company so that this seems more like a question for others to answer and less like an advertisement for your company - which I'm guessing is not what you were trying to do here. :)
    – Catija
    Jun 16, 2021 at 17:01
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    Why in the world is your company not specifying this in the Owner's Manual which I sure hope is provided with the product? This situation makes no sense!
    – Carl Witthoft
    Jun 16, 2021 at 18:14
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    It strikes me as very odd that a company that makes fireplace doors wouldn't know whether the doors should be open or closed when the fire is burning. Seems that Catija was very generous in editing this into an actual question instead of closing/deleting it as spam.
    – FreeMan
    Jun 16, 2021 at 18:27
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    They make replacement glass, not the doors. I'm sure it is specified in the owner's manual. The problem is they're asking the glass guy who has no idea what fireplace it is, and it very much depends on the type of fireplace. Masonry, you can basically do w/e you want as long as you're willing to replace the occasional cracked pane. All other types have extremely specific requirements.
    – Mazura
    Jun 16, 2021 at 19:08
  • wow, ruff crowd. We mfg the glass only, not the doors. We typically never even see the units that the glass is going it. I field a lot of questions on this subject and i know how we answer the question. I was just looking for other ideas. Forget i even asked!
    – Mike Monaghan
    Jun 17, 2021 at 18:11

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Is there a safety reason for one or the other? A performance reason?

Be sure to read any documents (instructions or user manual) that came with the doors (if they are a separate product) or stove (if the doors are built in to a product like a wood burner).

Any safety instructions will be in those documents.

As a manufacturer of glass for doors you should be referring those customers with such questions to their documentation or to the manufacturer of the doors.

As for performance:

A popular misconception is that fireplace doors are able to increase the efficiency and heat output of masonry fireplaces.

The purpose of glass doors on a fireplace is not to increase heat output or efficiency of open fires.

Manufacturers of fireplace doors typically state that the doors must be open during and for a while after fires. Studies and research have also shown that closed fireplace doors do not increase either heat output or efficiency

(emphasis mine)

Source: Fireplace Doors (The Complete Fireplace Glass Door Guide)

3 Really Good Reasons to NOT Burn a Fire with Your Doors Closed

  1. You will shatter your glass doors. Standard tempered glass is made to withstand temperature up to about 450 degrees. Typical fireplaces reach temperatures between 500 and 1200 degrees. Ceramic glass is designed to withstand temperatures up to about 1400 degrees.

  2. It is not safe. Masonry fireplaces are all brick or stone which absorb and reflect the heat much better than metal prefab fireplaces. Additionally, prefab zero clearance fireplaces are surrounded by wood which can be a combustible fire hazard, therefore have specific regulations regarding the ventilation of fireplace doors.

  3. You lose the fire’s heat. With the doors closed 99% of the heat of your fireplace with go directly up the chimney.

(emphasis mine)

Source: Should you keep your fireplace doors open or closed? - Brick-Anew

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  • Fire safety doesn't change just because the manufacturer says not to close them so that they don't break under warranty. With the doors closed 99% of the heat in your house DOES NOT go up your chimney (stack effect; in cold climates, all chimneys are always a net loss in heat, no matter what). So according to the manufacturers, if I need to leave the fire unattended I have to put it out? Yeah, IDTS. That's what the doors are for.
    – Mazura
    Jun 16, 2021 at 18:44
  • Keeping the doors (mostly) closed prevents sparks from shooting into the room, so it's safer for fire prevention
    – Phil Freedenberg
    Jun 16, 2021 at 19:38

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