Do I measure firebox height to the damper or to the top of the opening?
Measure both. Height to the top of the finished opening (the lintel) tells you the size of the opening itself, but the height to the damper is usually the lower, tighter clearance an insert or log set actually has to work around. Record both numbers — the damper often decides fit more than the opening height does.
Two heights, two purposes
The opening height — firebox floor up to the lintel — describes the visible face and the span you see. The damper height — floor up to the closed or framed damper throat — is the working clearance, and it's frequently lower than the opening. For an insert that has to pass a flue collar and liner up through the damper throat and smoke shelf, that throat is often the real choke point, not the roomy face.
Logs versus inserts change what matters
For gas logs, the height to the top of the opening matters most — it governs flame clearance and how tall a log set will fit, and a tall set simply won't clear a low opening. For an insert, the damper and smoke shelf usually govern, because we run a stainless liner up the flue and typically clamp or remove the damper so it stays permanently open around the liner. Same firebox, two different limiting numbers depending on what's going in.
Give us both and let us check the throat
Write down the opening height and the damper height, and if you can, note whether the damper is a simple throat plate or a heavier cast assembly. On the in-home assessment we look past the numbers at the throat, smoke shelf, and flue to confirm the whole path is clear for a liner or a log set. It's a quick check that saves a wrong order. Call (828) 545-0525 or request a free quote.
How we can help
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