System 2000 EK2 Frontier 175,000 vs 250,000 BTU/hr

Both rows use the EK2 energy converter with 4 gallons of water content, a 350 lb converter weight (plus 110 lb of jacket and insulation) and the same 10-foot counter-flow flue passage. The printed difference is capacity: 175,000 BTU/hr input with 149,000 BTU/hr gross output at 85% AFUE natural gas, versus 250,000 input with 204,000 output at 82%.

The propane columns run higher on both rows — 153,000 BTU/hr at 87% on the 175,000 row and 209,000 BTU/hr at 84% on the 250,000 row — which is the data sheet's pattern across the line. A 37% output increase costs three points of AFUE on natural gas.

System 2000 pairs either converter with the Energy Manager control and a storage tank for domestic hot water, so the sizing decision belongs to a heat-loss calculation plus the hot-water load, not to the boiler's maximum rating. In a home that never approaches 149,000 BTU/hr of load, the larger row simply gives up efficiency for capacity it cannot use.