Could anyone help me understand the calculation for the minimum efficiency of gas storage water heaters per the table above? The calculation is 80%Et (Q/800+110 SqRt V) SL, Btuh. I understand that Q is the nameplate input rate in Btuh and V is the volume. Do I use the volume of the whole system, the storage tank only or the recovery rate volume? I understand SL is the standby loss. Does SL, Btuh mean multiply the equation in parenthesis by the standby loss in btu's per hour? Thanks for the help, Paul Diglio