Hello, I am new to the forum, however I have been burning coal for several years. I currently have the small Morso Squirrel placed into my fireplace. This is a very small stove, only holds 5 lbs. of fuel, compared to my previous coal stoves, but it does a fairly good job, rated at 30,000 BTUs and will heat 750 sq ft. I am looking to replace the Morso with a Keystoker HF 70/90 insert into my fireplace which is very small. The opening measures 25" wide, 16 1/2" deep and 27 1/2" high, actually it was used with an old coal grate & canal coal, my house was built around 1889. Does anyone on the forum have a Keystoker insert currently in used ? If so, can you provide some rating for this unit. I have spoken to the reps at Keystoker, but would really like to know how well this type of insert is actually performing for a coal burner. Thanks.