The Least Sexy and Most Effective Way to Slash Your Home’s Carbon Footprint

In February 2020, our home’s carbon footprint was 64% lower than it was in February 2019. In June 2020, our home’s carbon footprint was 61% lower than it was in June 2019. I love our solar panels, but they only accounted for 6% of the February difference and 39% of the June difference. The real game changer? Probably not the first thing you’d picture when imagining a clean energy future, or the first image you’d see in a presentation about climate change, but perhaps the most important tool in our family’s quest towards net zero: a new, energy-efficient HVAC system. (Thanks to Andrew, master of spreadsheets, for crunching the numbers on our home energy use to compare year over year with the changes we’ve made, including converting between therms of natural gas and kwH of electricity as we’ve transitioned mostly away from natural gas. The actual difference between 2019 and 2020 is even more dramatic than the percentages above indicate, since charging our car is included in home energy use for 2020, and we use only a small fraction as much gasoline as we did before getting a plug-in hybrid. I’m happy to share raw data about our home energy use in more detail with anyone who’s interested).  

In 2019, when we started in earnest to plan how to cut our family’s carbon footprint, we thought about the biggest contributors to our country’s emissions: transportation (28%), electricity (27%, but more like 39% if lumped into the home/commercial building category including natural gas for heat and waste management), food (10%), and industry—basically “stuff” that’s produced that we buy (22%). So we knew our home’s electricity and natural gas use was a big chunk of our carbon footprint we needed to tackle. Sixty-three percent of our country’s electricity comes from burning fossil fuels, and for GA Power, it’s 69%. To get to net zero, we need renewable energy production to equal our energy use. We need to majorly ramp up renewable energy production, but it’s actually much lower hanging fruit (cheaper and easier) to lower our energy use through energy efficiency and reduction of energy waste and leakage. We absolutely need both to reach carbon neutrality, but energy efficiency arguably doesn’t get the attention it deserves. This post will focus on HVAC related energy savings, but stay tuned for a future post about energy efficiency in the rest of your home. 

Around 55% of the energy used in US homes goes towards heating and cooling. So unless you live somewhere with unusually mild weather year-round, the HVAC chunk of your energy use is probably where you’ll have the biggest bang for your buck in making a big reduction. We can see this on a larger scale in cities’ plans for transitioning towards clean energy: in Atlanta’s plan to transition to 100% clean energy by 2035, it’s estimated that the city can reduce its energy use by 25-30% via efficiency, mostly by insulating old homes and replacing old HVAC systems, and get an incredible return on investment in doing so. 

We had a basic idea of where most of our home energy use was likely coming from based on the above research, but to make a specific plan, we needed to know more in detail for our home. GA Power offers a rebate for a large chunk of a home energy audit, and similar programs exist in other states. We had Energy Consulting Services audit our home and were very happy with them. They put together a thermal map of our home so we could see where heat or cool air was escaping. Our windows were already double paned and doing a good job at insulation, but if yours are older or single paned, replacing them is a high yield way to lower your home heating and cooling use, often by a third or more. ECS recommended putting these cheap foam insulators behind our light switch and outlet covers (fun for kids to help with), seal around window frames and baseboards with clear caulk, and make some minor upgrades to our attic insulation (ECS as part of the audit makes a detailed “work list” in order of energy savings priority and recommended as DIY vs contractor, and they have a partner company you can optionally use to complete recommended work, which also can qualify for rebates through GA Power). 

Our highest yield change, though, wasn’t insulation but rather updating our HVAC system. Our old one was 17 years old and 10 SEER (Seasonal Energy Efficiency Rating), which is inversely proportional to the energy used (so the higher the SEER, the better). The very best option for an HVAC system with a minimal carbon footprint is a geothermal system, which uses pipes that go deep underground to take advantage of the ground’s more constant temperature compared to the air, to release heat from your home into the ground in the summer and transport heat from the ground to your home in the winter. A geothermal system can perform at around 45 SEER, meaning it would use less than a quarter as much energy as our old HVAC system. There’s a 26% federal tax credit for installing a geothermal system, and you should eventually get a full return on investment in energy savings, but for us, the cost was prohibitive (plus in our case the only feasible place to install the deep pipes would have been beneath our driveway so we would have had to repave part of it–not the case for everyone’s home/yard though!). Geothermal systems seem to be more cost effective when incorporated into new construction–something to consider if you’re building a new home or have a chance to give input on new construction in your city, business, university, etc.

For more standard HVAC systems, the newer models are available with a max SEER of about 22, and also have rebates available and will eventually give you a return on investment in energy savings (and are more affordable than geothermal systems). We had a few companies come out to give us proposals/quotes, and we ended up going with Stuart Pro Heating and Air, and the TRANE XV20i DUAL FUEL HEAT PUMP W/ XC95 NAT/GAS FURNACE, with a 22 SEER rating and a smart thermostat. We were a little torn between getting a fully electric heat pump vs. the dual fuel one we ended up choosing. The dual fuel one works as an energy efficient electric heat pump for air conditioning and for most heat (when outdoor temperature is above 30 degrees or so). When the temperature dips particularly low, the natural gas kicks in. Ideally, if we are going to get to net zero carbon emissions, we shouldn’t be using any natural gas. And we really liked the idea of sticking it to the natural gas company by closing our account and not paying the monthly base rate. But, considering that the all-electric heat pump is less efficient in very cold weather, and that the GA Power grid is not anywhere close to all renewable, the dual fuel system has the overall lower carbon footprint. I hope that in another 15-20 years when we need to replace our dual fuel system, the grid may be green enough that the all-electric option has the lower (or maybe even nonexistent) carbon footprint. We were able to get a lower base monthly rate for natural gas after demonstrating our minimal use, and we close our natural gas account for the warmer months of the year. We also had our old ductwork redone to avoid leakage, so our heating and cooling related energy use ended up decreasing by more than the 55% we’d expect based on the improved SEER rating alone.

If you’re not in a place to replace your HVAC system (or replace windows or insulation), there are some free (or very cheap) and easy ways to chip away at your heating and cooling related energy use. Be sure that vents are open and aren’t covered or partially blocked by furniture or clutter. If you have a programmable thermostat, set it to run the heat or air conditioning lower during the night and adjust your thermostat when out of town or away from home for the day. Use fans in the summer and sweatshirts and blankets in the winter so that you can feel comfortable tweaking the temperature towards using less heat or AC. If the sun shines directly into a window, keep curtains open on cold days and closed on hot days. Install the socket sealers I mentioned above, and apply clear silicone caulk around window frames and where the baseboard meets the floor. Avoid keeping doors or windows open on hot or cold days. There are various types of inexpensive weather seals you can apply to the bottoms of doors to avoid heat or cool air escaping. 

We love our HVAC system. It runs reliably and keeps us comfortable using a fraction of the energy our old one used. Replacing an old one is a great investment for the planet and for lowering your electricity and/or gas bills, especially as extreme weather increases and we rely even more on our homes’ heating and cooling systems. If you’re not needing or able to replace yours now, keep efficiency in mind in the future when you need to replace an old or broken system, and use your influence at your workplace, school, or church when decisions are being made about upgrading buildings, so that we can keep lowering that bar of total energy use to get it low enough for renewable energy production to reach it. 

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