Each of the 100 homes has a fixed floor area and a randomly assigned pre-retrofit income and building envelope quality (U-value). Seasonal heat loss uses the standard degree-day method:
HDD = max(0, Tbase - Tout) x 151 (days in the heating season)
Q (kWh) = U x A x HDD x 24 / 1000
Annual cost = Q x fuel price ($/kWh)
Energy burden = (Annual cost / 12) / (monthly income) x 100%
A household is classed "fuel poor" once its burden crosses the widely used 10% threshold (the original UK fuel-poverty definition, still used as a benchmark today). Retrofitting a home roughly halves its U-value (better insulation, less heat escapes per degree-day), which is why the retrofit slider directly moves red tiles toward green.
- Outdoor temp — colder winters raise degree-days and every home's heating demand together.
- Fuel price — scales the cost side of the burden ratio for everyone at once.
- Retrofit % — upgrades that fraction of the worst-insulated homes first (the ones the policy would target).
- Income inequality — reshapes the income distribution from roughly even to heavily skewed, without changing total neighborhood income — showing burden is driven by distribution, not just averages.
The grid panel's tile size encodes monthly income (in Income mode) and its color always encodes energy burden (green → low, red → at/above the fuel-poverty line) unless a different palette mode is chosen. The histogram shows how burden is spread across all 100 homes; the scatter plot shows income vs. heat bill, with the diagonal 10%-burden line drawn in.