How about giving this a whirl? There are a lot of stove owners represented here. Many times it's hard to find the practical firebox dimensions of a particular model. That is, the size of the maximum rectangular box that could fit inside. The manufacturer sometimes publishes the total ft3 of the firebox. I'll start: Stove Make and Model: Hampton HI300 insert Measured Practical Firebox Dimensions: 19.25"l x 18.25"w x 10.75"h Measured Practical Firebox Capacity: 2.19 ft3 Manufacturer's Stated Firebox Capacity: 2.3 ft3.