Wood Heater Glass Replacement: Measuring and Sizing Guide

Replacement glass for a wood heater is sized from the manufacturer’s part number or the old panel itself, not from the door opening.

Measuring the door frame is the most common way people order the wrong pane — several manuals require the glass to overlap the opening under the retainers, so an opening-sized panel leaves nothing to clamp down. The sequence: identify the exact model, read the glass spec from the manual, then confirm dimensions against the old panel before a single dollar moves.

What Specifies The Correct Glass For Your Stove

The manual and rating plate settle every sizing question and should be checked before any measuring. Wood stove glass is high-temperature ceramic — not window glass, not tempered fireplace glass — listed by thickness and part number.

• Drolet Escape 1800 specifies ceramic glass 5/32 in (4 mm) thick and 17 in × 10 1/16 in, rated to 1,400°F, supplied as SCHOTT ceramic glass through a dealer.
• Hearth & Home Technologies Model 400 uses 5 mm ceramic glass, part 20912.
• True North TN20 takes ceramic glass only, 9 1/4 in × 13 1/4 in (235 mm × 337 mm), 5 mm thick.
• Harman Exception calls for Harman replacement panels rather than substitutes, bedded on 1/4-in self-adhesive gasket.
• Parlour T-4000 requires 5 mm ceramic glass.

Note the pattern: 4 mm and 5 mm are not interchangeable, and the two are easy to confuse with a tape measure. The Drolet dimension also runs past 17 inches on one side, which many generic panes do not cover.

How To Measure A Wood Stove Glass Panel

Measure the old glass itself, out of the door, with the stove cold — outside width, outside height, thickness, and shape, not the hole it sat in.

1. Read the model, revision, and serial range off the rating plate and confirm against the manual.
2. Let the stove burn out completely and cool. Broken glass plus a warm firebox is how people get cut.
3. Photograph the panel in place first to record retainer and gasket positions.
4. Remove the door and lay it face-down on a padded surface.
5. Pull the retainers or screws, lift out the old glass, and clear every fragment.
6. Measure outside width, outside height, and thickness with calipers or a good rule. For arched or notched panels, measure at several points and cut a paper template.
7. Note whether the manual’s figures describe the glass size, the visible area, or the door opening — the Model 400 instructions have the glass edges overlap the opening evenly.

Once the numbers are on paper, the sizing decision is largely made. To compare ready-made panels instead of chasing a dealer, this roundup of wood heater glass replacement options pairs each panel with the models it fits.

Common Sizing Errors And Safety Rules

Manuals are blunt: a cracked or broken panel must be replaced before the stove is run again. The True North TN20 and Harman Exception manuals both state it outright.

The failures repeat predictably. Ordering by brand alone instead of exact model, version, and part number is the big one — model families carry more than one glass size. Measuring the door opening instead of the panel is next. Substituting tempered fireplace glass or household glass for ceramic is the third and most dangerous: ceramic glass is built for heat tempered glass is not.

Two details decide whether the job lasts. Gasket must match the original type and cover the full perimeter; the Drolet manual centers the pane and warns against overtightening the retaining screw, while the Model 400 instructions tighten retainers a few turns at a time, alternating until snug. Compressed or contaminated gasket lets air past the glass and can crack a new panel. Confirm the part number with a dealer when the manual lists one; if it only gives dimensions, match thickness and shape exactly.

Does The Glass Thickness Really Matter?

Yes — thickness is part of the specification, not a rough guide. A 4 mm pane in a door built for 5 mm sits loose under the retainers, and a 5 mm pane in a 4 mm channel will not seat; either way the gasket cannot seal evenly.

The same applies to glass type. The Drolet manual calls for SCHOTT ceramic glass to the listed specification, and the Harman manual directs users to Harman panels rather than substitutes. Matching the part number removes the guesswork.