Remember classroom field trips to the library? Those were your most eco-friendly days of...

Cherry, maple, oak, elm and other deciduous trees fall into this category of wood. They are slower-growing trees than softwood conifers such as pine, and are sources of durable, valuable, and undeniably good-looking timber for flooring and furniture. The market for hardwoods has led to damaging forestry practices the world over, but some logging companies harvest more gently; when shopping for hardwood products, look for those certified by Forest Stewardship Council (FSC)-a sign that the wood came from a sustainable, well managed forest. Salvaged hardwood (rescued from buildings scheduled for demolition, for example) is another tree-friendly choice.

Many homeowners know very little about their heating and cooling equipment-until something goes...