  This paper explores the impacts of decarbonisation of heat on demand and
subsequently on the generation capacity required to secure against system
adequacy standards. Gas demand is explored as a proxy variable for modelling
the electrification of heating demand in existing housing stock, with a focus
on impacts on timescales of capacity markets (up to four years ahead). The work
considers the systemic changes that electrification of heating could introduce,
including biases that could be introduced if legacy modelling approaches
continue to prevail. Covariates from gas and electrical regression models are
combined to form a novel, time-collapsed system model, with demand-weather
sensitivities determined using lasso-regularized linear regression. It is
shown, using a GB case study with one million domestic heat pump installations
per year, that the sensitivity of electrical system demand to temperature (and
subsequently sensitivities to cold/warm winter seasons) could increase by 50%
following four years of heat demand electrification. A central estimate of 1.75
kW additional peak demand per heat pump is estimated, with variability across
three published heat demand profiles leading to a range of more than 14 GW in
the most extreme cases. It is shown that the legacy approach of scaling
historic demand, as compared to the explicit modelling of heat, could lead to
over-procurement of 0.79 GW due to bias in estimates of additional capacity to
secure. Failure to address this issue could lead to {\pounds}100m overspend on
capacity over ten years.
