Below are the design parameters supplied by my contractor after an on-site survey. Not sure what is meant by Winter/Summer Design or temp diff values:

Design Data:	Comfort Conditions:
Heating Load: 51,000 Btuh	Heating Setpoint: 68 °F
Heating Temp Diff: 68 °F	Cooling Setpoint: 74 °F
Cooling Load: 30,000 Btuh	Start Cooling Temp: 74 °F
Cooling Temp Diff: 17 °F	HW Temp Setting: 130 °F
Constant Fan: No	HW Users: 3 people
Design City: MINNEAPOLIS, MN	Annual Loads:
Winter Design: -12 °F	Heating: 109.9 million Btu
Summer Design: 92 °F	Cooling: 14.6 million Btu
Bldg Bal Temp: 56.7 °F	Hot Water: 17.3 million Btu
Internal Gains: 8,490 Btuh	HW Use - Daily: 55.0 gallons

Winter design is how cold it might get in your location in the winter
Summer design is how hot it might get in your location in the summer

The temp diff for summer seems right 92 - 17 = 75

The temp diff for winter seems off 68 - 68 not = -12

Temp diff for winter should be 80

Are you going to be happy with an inside temp of 68° in the winter?

It seems to me, Pipemajor's contractor defined Heating Temperature Differential as the difference between winter design temp (-12) and building balance point (rounded down to 56), thus: 56 - (-12) = 68 degrees. I think Heating Temp Diff, as Dewayne pointed out, is the difference between heating setpoint and winter design temps, therefore: 68 - (-12) = 80 degrees. Concern is that proper figures are put into load calc software, and building balance point, as well as internal gains are accounted for.

Regards, Masoud

What is a Building Balance Temperature???

Temp where internal building sources of heat (people, lights, appliances, cooking) and possibly also solar gain taken together equal the heat loss. Below the balance point the heating system must run to maintain setpoint.