Insulation reduces marginal heating cost and may lead to a takeback effect of higher wintertime thermostat settings, with a consequent dilution of energy savings. Alternatively, additional insulation could permit a lower thermostat setting by reducing drafts and radiation while increasing moisture retention, thereby enhancing comfort. This paper evaluates thermostat net takeback, the difference between takeback and enhanced comfort. Evidence supports the existence of both effects, with net takeback at the low end of literature estimates. Net thermostat takeback is on the order of 0.05 degrees F, leading to an energy takeback that ranges from 1-3% of potential energy savings, depending on climate and house size. Other significant determinants of thermostat are heating energy price and the presence of elderly or young occupants.