As you can see in the following table, the E-Classic 1400 furnace holds almost 10 times more wood, has a higher furnace efficiency, and has a higher rated output over 8 hours than the BIS Ultra fireplace.  It has certainly been easier to load up the outdoor furnace once a day (or often twice when it's cold).  In practice, with our well-insulated house, we typically use the fireplace when it's above freezing outside because the fireplace has enough capacity to keep the house warm.  Using the e-Classic 1400 takes longer because of the time it takes to bring all of the furnace's water up to operating temperature and this light load tends to cause creosote build-up. Besides, a crackling fire in the fireplace is nice in the winter.

Although a 32" long log can fit into the firebox, the maximum log length of wood splitter will determine actual log lengths.  The dealer who sold me the E-Classic 1400 recommended 24" logs and this seems to be fairly common size for wood splitters too.

Specification  E-Classic 1400 BIS Ultra
Door 18.5" x 18.5" 25" x 14" (glass area)
Firebox 32" L x 24" W x 32.5" H
14.44 ft³ volume
25"W x 13.5"D x 13"H (nominal)
18"W x 12"D x 12"H (practical)
2.5 ft³ (nominal) / 1.5 ft³ (practical)
18"-19" log
Weight 2,085 lbs. 402 lbs.
Water Capacity 195 Gallons N/A
8-Hr Output Rating 107,459 BTU/hr †
(based on dry oak)
12-Hr Output Rating 72,000 BTU/hr  
Maximum Heat Output Capacity 209,316 BTU/hr †
(based on dry oak)
up to 60,000 BTU/hr
up to 8 hrs burn time
EPA Rating   4.8 grams/hr
Furnace Efficiency over 84% 75.2%
Note † Based on EPA qualifying test  tapered firebox is 18" wide
at the back