OK, you are getting close to the summit. Keep going!!! The bottom line is, resolving the climate crisis will require digging deep—but that doesn’t mean our lives won’t be equally or more satisfying than the one we transition from.

Install a heat pump for home heating. We have already covered the low hanging fruit of electrification—now it’s time to invest in a heat pump to heat your home. Heat pumps are about three times more efficient than gas or electric resistance heating—and because they are electric they can be powered by renewable electricity.

What’s a heat pump? Heat pumps essentially function as air conditioners that can run in reverse and also provide heat, as well as cooling. Without getting overly technical, there are two primary system types for homes—air source and ground source. Air source heat pumps have outdoor compressor units with either horizontal or vertical fans. Ground source heat pumps have piping in the ground, either close to the surface, or in a deep vertical well; the heat pump itself is typically located inside the house. Ground source heat pumps are more efficient and work very well in very cold climates. For most colder locations (i.e., freezes outside at times), I recommend a cold temperature air source heat pump—in particular the cold climate model made by Mitsubishi. These units feature a special compressor able to create heat even in outdoor temperatures well below freezing.

There are two primary ways heating can be distributed within the home—either through ducting, or through individual ductless distribution units that mount on the wall or in the ceiling. For homes with existing ducting, probably the most straightforward retrofit is to remove the furnace and replace it with a whole house heat pump air handler. Another alternative is to add ductless units to primary living areas, with smaller satellite ducted air handlers for smaller rooms—while likely more efficient, this will also likely be more expensive and disruptive.

Aggressively air seal and install a Heat Recovery Ventilator (HRV). A green building maxim is “Build tight, and ventilate right”—which means sealing your home’s exterior so you don’t leak all that precious heat or cold to the outside, and ensuring you have adequate fresh air. How do you do that? I discussed air sealing basics in Tier Three…now I recommend you go all the way and very tightly seal your house, while at the same time installing a heat or energy recovery ventilator.

A heat recovery ventilator (HRV) is a cool, two-way device that exhausts stale interior air and brings in fresh outside air. It uses the interior air (which is at a nice comfortable temperature) to pre-warm or pre-cool fresh air by means of a labyrinth which runs the exhaust and fresh air by each other. It can either be tied into an existing duct system or use an independent set of ventilation-only ducts. Typically, exhaust air comes out of bathrooms and the kitchen, and the fresh air is vented into bedrooms. An energy recovery ventilator (ERV) is a more sophisticated version of an HRV that moderates humidity levels in very cold and humid climates. The beauty of an HRV/ERV is that they provide ample ventilation into the home without a substantial energy penalty—typically retaining 75-85% of the thermal energy of the exhaust air.

With adequate, balanced ventilation, the home can then be sealed as tightly as possible. This is a key strategy of Passive Houses, which enables very minimal mechanical heating and cooling. Retrofitting a home to be super tight is challenging and requires the use of a blower door to identify leaks and measure the home’s leakage rate.

For those of you really getting into decarbonization home improvement DIY, I’d like to highlight Green Building Advisor as a great resource on an array of efficiency topics.

Use no fossil fuels for getting around, except for transit and air travel as a rare treat. Getting to a zero-carbon life gets tough on the margins. Ground transportation is starting to be electrified, which can then be powered by renewable electricity. Fossil-fuel-powered transit has a low enough carbon footprint that a dispensation is ok until it electrifies.

Flying just continues to be tough. Remarkably, in Europe, where high speed rail is ubiquitous, short haul flights are starting to be prohibited, and a strong cultural movement is underway to simply stop flying. While early steps are underway to power airplanes with biofuels, we are a long way from them mainstreaming—frankly, the aviation biofuel revolution lags much too far behind the rest of our technologies.

A friend of mine recently gave me a hard jostle when he essentially said, “Well, there’s no going back on frequent flying—it’s a necessity.” The truth is, it isn’t. We did just fine a handful of decades ago when flying was a rare treat. A drop in demand, or even the threat of it, will help accelerate the biofuel revolution in aviation.

Eat a vegan diet, and eliminate packaged and frozen foods. The bottom line is, a plant-based diet has a much lower footprint than one that includes meat and animal products. The many healthy, happy vegans out there show that thriving on a plant-based diet is more than possible.

Move to a dense, highly transit served center. This doesn’t automatically make you a lower carbon liver, and the obverse (rural living) doesn’t doom you to a high carbon life—but, generally speaking, living in a dense urban area makes it easier to reduce your climate impact.