Houses in cold climates are kept warmer in winter than those in warm climates, des pite the greater cost of heating in colder climates. It is shown that this is not only consistent with, but also implied by, rationality. The contrary intuition is based on a confusion between average and ma rginal cost. The same analysis implies that it is rational to keep th e thermostat setting constant throughout the heating season rather th an changing it with changes in external temperature.

This paper uses computable general equilibrium models to demonstrate that partial-equilibrium welfare measures can offer reasonable approximations of the true welfare changes for large exogenous changes. With consistency in the size and direction of the indirect price effects associated with large shocks, single-sector partial-equilibrium measures will exhibit small errors. Otherwise the errors can be substantial and difficult to sign.