IECC 2012

This batch of simulations represents a code-built IECC 2012 home with both natural gas and electric varieties. Heating, cooling, and water heating equipment meets the federal standard as of July 29, 2016. A natural gas and electric version of the code home is run in each location. Each of vented crawlspace, conditioned basement, and slab on grade foundation types are run as well.

Base Inputs

The hescore inputs that are the same between runs are:

'building_address': {
    'assessment_type': 'initial',
'building': {
    'about': {
        'shape': 'rectangle',
        'year_built': 2016,
        'number_bedrooms': 4,
        'num_floor_above_grade': 2,
        'floor_to_ceiling_height': 8,
        'conditioned_floor_area': 2200,
        'orientation': 'south',
        'blower_door_test': False,
        'air_sealing_present': True,
    'zone': {
        'wall_construction_same': False,
        'window_construction_same': False,
        'zone_roof': [
                'roof_name': 'roof1',
                'roof_assembly_code': 'rfwf00co',
                'roof_color': 'medium',
                'roof_type': 'vented_attic',
                'zone_skylight': {
                    'skylight_area': 0,
        'zone_floor': [
                'floor_name': 'floor1',
        'zone_wall': [],

    'systems': {
        'hvac': [
                'hvac_name': 'hvac1',
                'hvac_fraction': 1,
                'heating': {
                    'efficiency_method': 'user'
                'cooling': {
                    'efficiency_method': 'user'
                'hvac_distribution': [
                        'name': 'duct1',
                        'location': 'cond_space',
                        'fraction': 100,
                        'insulated': True,
                        'sealed': True,
        'domestic_hot_water': {
            'category': 'unit',
            'type': 'storage',
            'efficiency_method': 'user'

Other inputs change based on the IECC climate zone and state as required by IECC and equipment federal standards.

Air Sealing

IECC 2012 specifies that the building should be air sealed:

The building thermal envelope shall be constructed to limit air leakage in accordance with the requirements of Sections R402.4.1 and R402.4.4

However, it doesn’t specify a particular target infiltration measurement. Therefore, we choose to say that according to HEScore, the house is air sealed.

Roof and Ceiling Construction

The house has a vented attic with a ceiling R-value that changes based on the IECC Zone:

IECC Zone Ceiling R-value
1 30
2-3 38
4-8 49

Foundation Insulation Levels

The code home can be run with a few different foundation types. The default is vented crawlspace, but we will document each here.

Vented Crawlspace (default)

The foundation wall R-value is 0.

The floor assembly R-value is determined by the IECC climate zone:

IECC Zone Floor R-value
1-2 13
3 and 4 excluding marine 19
4 marine and 5-6 30
7-8 38

Conditioned Basement

The floor assembly R-value is 0.

The basement wall R-values are determined by the climate zone:

IECC Zone Basement Wall R-value
1-2 0
3 11
4 excluding marine 11
4 marine and 5-8 19

Slab On Grade

The floor assembly R-value is 0.

The slabe R-value (foundation_insulation_level) is determined by climate zone:

IECC Zone Slab R-value
1-3 0
4-8 5


Wall assembly codes are determined by climate zone:

IECC Zone Wall Assembly Code Wall Assembly Description
1-2 ewwf13wo Wood Stud Wall with R-13 cavity insulation
3-5 ewps13wo Wood Stud Wall with R-13 cavity insulation and 1 inch of XPS sheathing
6-8 ewps21wo Wood Stud Wall with R-21 cavity insulation and 1 inch of XPS sheathing


Window Properties

Window U-value and SHGC are determined by climate zones. Where IECC 2012 doesn’t specify a U-value or SHGC for a particular climate zone, the U-value and SHGC from a double-paned, clear, air filled window from the National Residential Efficiency Measures Database was used.

IECC Zone U-value SHGC
1 0.49 0.25
2 0.40 0.25
3 0.35 0.25
4 except marine 0.35 0.40
4 marine and 5-8 0.32 0.56

Window Areas

The window areas are calculated to be 12% of the walls given a 5:3 aspect ratio with the longer side being the front/back.


Natural Gas

80 AFUE Natural Gas Central Furnace


8.2 HSPF Heat Pump


Natural Gas

Central Air Conditioner that meets the federal minimum standard efficiency level:

Region SEER
North 13
South 14
Southwest 14


14 SEER Heat Pump

All heat pumps are required by federal standard to have a minimum SEER of 14.

Domestic Hot Water

Natural Gas

Natural Gas storage water heater. Energy factor is calculated as per federal standard given the default tank size in HEScore of 40 gallons.

\[\begin{split}EF_{gas} &= 0.675 - ( 0.0015 \cdot V_{tank} ) \\ V_{tank} &= 40 \\ EF_{gas} &= 0.615\end{split}\]


Electric resistive storage water heater. The default size of electric water heater for HEScore is 50 gallons. At 50 gallons, a heat pump water heater is not required to meet federal standards. (At 55 gallons federal standard stipulates a water heater with an EF that can only be met by a heat pump water heater.) Energy factor is calculated as per federal standard.

\[\begin{split}EF_{ele} &= 0.960 - ( 0.0003 \cdot V_{tank} ) \\ V_{tank} &= 50 \\ EF_{ele} &= 0.945\end{split}\]