Heat/enthalpy recovery ventilators are a big one. In New England, you want maximum insulation and minimum air leakage. Without mitigation, this leads to poor ai

Heat/enthalpy recovery ventilators are a big one. In New England, you want maximum insulation and minimum air leakage. Without mitigation, this leads to poor air quality. Therefore you want air changes, but you don't wanna vent all your heat (in winter, cold in summer), so you exchange heat between incoming and outgoing air. HRVs only recover sensible (thermometer) heat but don't affect latent heat (humidity heat of vaporization) so there exist enthalpy recovery systems. However these run into icing problems in winter, when they would be most helpful. It's an area of active research. Ground-source heat pumps are the best thing ever for temperate regions, since you can actually store heat/cold between temperature cycles and even seasons, but rather expensive to install, unless you are already putting in a leach field. I'm hoping for some advances in tech to make laying geothermal loops cheaper, I.e. cheaper and easier directional drilling. E-glass (low emissivity) is increasingly popular. There's a cool trick where you have clerestory windows or skylights with e-coating to let in light but less IR. Then your south-facing regular windows have regular glass and big overhangs. This gives you year-round natural light and winter-only solar gain.