Fireplace opening 35-1/2" wide x 24" high in a 500 sq ft room. Inserts that fill the opening run 22,000-32,000 BTU. Seems like a lot of BTU's for 500 sq ft. I am not finding many options in the 15,000- 20,000 BTU range. What I am finding is glass bed not logs. Is that because of the flame height at the lower BTU? ? I am looking for a direct vent application.