By Johnathan Mason, Ace Chimney Service.
Glass doors on a masonry fireplace are one of those features people assume are always an improvement. They are useful, but mostly for a reason other than the one homeowners expect, and used incorrectly they make a fire worse. Here is the plain version for Fox River Grove households.
What they are actually for
Their main value is when there is no fire. An open fireplace with the damper shut still leaks, and a fireplace with the damper open is a hole in your house — heated air goes straight up it all winter. Closed glass doors on a cold fireplace cut that loss considerably. That is the benefit, and it is a real one.
Why closing them during a fire is usually wrong
An open masonry fireplace burns with room air. Close the doors and you throttle that supply, which makes the fire burn cooler and dirtier — and cool, smoky fires are what deposit creosote. Closed doors also trap heat against the glass and the frame, and on many units the manufacturer specifically says to operate with the doors fully open while burning. Check the label or the manual before assuming. When in doubt, burn with the doors open and the mesh screen closed for ember control.
The exception
Doors are typically closed as the fire dies down to coals, once flames are gone. That stops the remaining heat in the room from being pulled up the flue overnight while the coals finish. Manufactured units and inserts follow their own rules and are often designed to run closed — those are sealed appliances, not open fireplaces, and the guidance is the reverse.
Heat, glass, and cleaning
Tempered glass in a fireplace door is not the same as the ceramic glass in a stove. It is not intended to sit directly against sustained flame contact. Keep the fire back from the glass, and clean the haze off with a proper fireplace glass cleaner or damp newspaper dipped in fine wood ash — not an abrasive pad, which scratches the surface and makes the next film stick harder.
What doors will not do
They will not turn an open fireplace into an efficient heater. If heating the room is the goal, the answer is an insert with a properly sized liner, covered on our chimney relining page. They also do not reduce the need for sweeping. Whatever is on the front of the fireplace, the flue behind it still needs an annual inspection.
Ace Chimney Service is insured and bonded, has 29 years in the trade, gives the price up front, and works seven days a week from 7 AM to 7 PM serving Crystal Lake and McHenry County. Call (815) 320-0883.
Frequently asked questions
Should glass doors be open or closed while burning?
On an open masonry fireplace, generally open with the screen closed, unless the manufacturer says otherwise. Closing them restricts combustion air.
When should I close them?
Once flames are out and only coals remain, and whenever the fireplace is not in use.
Do glass doors save energy?
Yes, mainly by reducing air loss up the flue when there is no fire.
Why does the glass turn white or hazy?
Deposits from combustion, worse with damp wood and cool fires. Dry wood and hotter burns reduce it.
How do I clean fireplace glass?
A dedicated fireplace glass cleaner, or damp newspaper dipped in fine ash. Avoid abrasive pads.
Can I add doors to any fireplace?
Factory-built units require doors listed for that specific model. Fitting generic doors to a prefab is not acceptable.
The glass cracked — can I use it?
No. Replace the panel with the correct type before using the fireplace.
Do doors stop downdraft smells?
They help, but persistent odour usually means a damper, cap, or draft issue that is worth diagnosing.
Published September 13, 2026