Here is the issue - you can technically burn a fire with the fireplace doors closed and the draft assembly opened. The draft assembly will allow enough combustion air to feed the fire rather than having your glass doors wide open. How does this benefit you? Having the glass doors wide open means that a substantial amount of air from your room is feeding the fire. This is air that you have paid to heat – since you typically are using the fireplace in the winter time. Keeping the fireplace glass doors closed will limit the amount of air that the fire is using, which in theory will save you money because you are not using as much conditioned air. I have talked to a number of homeowners that tell me that when they have a fire burning in the fireplace with their fireplace doors wide open their furnace will be constantly running. This is because so much of the conditioned air is being sucked out of the room and up the chimney. When you combine the savings you receive by keeping the fireplace doors closed with the radiant heat from the fireplace, your net heat is substantially increased when you burn a fire with the fireplace doors closed.
So if the above method is a cost savings and even preferable; why is it controversial? The reason is that all fireplace door manufacturers warn that if you burn a fire in the fireplace with your doors closed, the lifetime warranty on the glass is voided. In other words, if the glass breaks while your burning with the doors closed, you will be responsible to replace the glass.
Your fireplace doors use tempered glass which is rated up to approximately 600 degrees Fahrenheit. This should be sufficient for any normal size fire however there are other factors that can contribute to glass breakage. Since each fireplace is unique and these factors unforeseeable, fireplace door manufactures require that you burn the fire with the doors open.
I would never tell you to do something that would void your warranty – BUT… if you were still going to do this despite your warranty being voided; here are a couple of things to keep in mind:
- Always keep the doors open when using gas logs. Do not ever burn gas logs with the fireplace doors closed. A gas fire is hotter than a wood burning fire.
- Don’t burn a bonfire in a fireplace! Keep the size of the fire reasonable.
- Keep the fire at least 6-8 back from the glass.
- Don’t go from 0 to 60 in 6 seconds! What I mean by this is; don’t get the fire too hot too quick. One of the reasons for the glass breaking is the quick change in temperature. All things in moderation.
- If you are really set on burning a hot fire with the fireplace doors closed, consider purchasing a fireplace door that features ceramic glass - such as the Sentry Fireplace Door. It's not inexpensive but it may be worth it depending on your desired application.
- If you were to have glass breakage - don't freak out. You can purchase replacement tempered glass on our website and it is really easy to install. It's also not that expensive.