A: See my answers below on the carbon footprint of manufacturing the fab four. On cradle-to-grave accounting for CO2, more and more people are starting to think about this. Let’s take each one of the fab four in turn:
- Heat pumps. This is my biggest concern because the refrigerant gas is a very potent greenhouse gas, it is about 1,000x as strong as CO2 in causing global warming. If the heat pump is put in a land fill, or recycled for its metal, then the refrigerant will escape into the atmosphere. I hope that eventually a new generation of low-global-warming-potential refrigerants will replace the current generation, which is called R410A. R410A is a hydrofluorocarbon (HFC) that was developed to replace chlorofluorocarbons (CFCs) because CFCs depleted the ozone layer. Other applications (like making the bubbles in spray-foam insulation) also use HFCs. HFCs for spray foam are beginning to be replaced with HFOs (hydrofluoro-olefins) because HFOs have only about the same global warming potential as CO2. Without a new generation of refrigerants, we are going to have to rely on installers to safely remove the refrigerant gas before the unit is disposed of. This is probably going to require legislation. In Paul Hawken’s book, “Drawdown, The Most Comprehensive Plan Ever Proposed to Reverse Global Warming”, refrigerant management (or mismanagement) is listed as the most addressable cause of global warming.
- Insulation. It is very easy to separate fiberglass or rockwool insulation from the wooden framing of a house when the house is demolished. It is very hard to separate spray foam from the wood because it is stuck to the wood like glue. This, plus the flammability of spray foam (which is almost never discussed) is why I prefer either fiberglass or rockwool for insulation. Since both fiberglass and rockwool and very porous to drafts, they need to be installed with an air-tight but breathable membrane. Fiberglass and rockwool can either be reused or recycled.
- Triple-glazed windows. These pose no additional problems at the end of their life than any other window. The glass and wood can easily be separated and recycled or disposed of in a landfill where the glass will stay forever.
- Solar panels. A solar panel is essentially glass plus some metal. Both are valuable and easy to recycle.