Unless you live somewhere like San Diego, a significant amount of your utility bills will go towards maintaining your living space at a comfortable temperature. There are ways to minimize these expenditures to help you save more money for or during your early retirement.
The temperature in your house is determined entirely by the laws of thermodynamics. If it is very hot outside then that heat energy wants to move inside. if it’s very cold outside then the heat energy in your house wants to move out. This is what leads to the internal temperature becoming uncomfortable. The bigger the difference in temperature between outside and in the faster the inner temperature will change. Insulation is your first line of defense, although unless you are actively building your own house there is little you can do to change your existing home’s insulation.
Windows and doors are a major source of temperature leaks. Many places have cheap single pane windows that will very poorly keep away outside temperature. You can upgrade windows to superior dual-pane glass windows, however the cost of this upgrade and the money you are expected to save from it means you might not break even for years. Doors, and the gaps around them, are another major source of heat transfer. Replacing doors aren’t very cheap either but you can put some plastic insulating guard around the frame to fill the gaps.
The best strategy is to set your home’s temperature to be as close to the outdoor temperature as possible while still remaining comfortable. Humans are actually very adaptable animals that can survive in a broad range of temperatures. There are humans that work outside in the arctic in -40°F and in deserts up to 120°F. My personal comfort range is around 65°F – 85°F. In the hot summer I set the thermostat to about 85 and in the winter I let my house cool down to 65. DO NOT be like one of those people who complain whenever the temperature is not perfectly 72°F. If you feel too hot at higher temperatures then it either means you need to let your body adapt, or you need to lose weight. It’s proven that overweight people hold on to body heat more than skinny people, so if you want to save on your AC bill: loose that weight.
If you live an apartment there’s another very significant way to keep your temperature stable. Use your neighbors to moderate the temperature. Typically in an apartment you might share up to 5 sides with an adjoining apartment. The more sides you share the more likely your apartment will match the temperatures of your neighbors. I once lived in a first floor apartment with neighbors on all 3 sides and above me as well. Not once did I use heat or AC and the temperature never strayed from 70-80 degrees. Why would I spend money on utilities when my neighbors were already doing it for me? Giving the reality of Early Retirement, you can expect no one is as interested in frugal living as you are. If it’s a hot day, your neighbors are going to turn the AC down to 72°, because that’s what people do. it might not get that cold in your apartment but 80° is still very tolerable, and that money you saves means you don’t have to go to a job anymore. Let your neighbors suck on that.
Another great trick to handle your house’s heat is to use carefully planned open windows and fans. It’s one of my favorite tricks since I love outside air. During the cooler months you should open your windows during the day when it is warmer outside than in your house. in the warm months do the opposite and open your windows at night when it’s cooler. Use a fan to supercharge this affect, it costs much less to run a fan than your central AC or heat. If the temperature difference is great enough an open window and a fan can be just as effective. I especially like to super-cool my apartment at night using windows and fans during the summer. Let the temperature in your house get as cold as possible because once the sun rises it’s going to heat things up fast. Close the windows when it gets hot and if you did it right you will not have to turn on the AC at all that day. Letting the temperature fluctuate naturally this way with the daily cycle is much more energy efficient than trying to maintain a single temperature.
There is some debate on how to use fans in windows. Should it be blowing in, or out? What size of fan should I use? I prefer blowing out but that also means you need at least one other open window somewhere else in your house that will have outside air moving in. This means the temperature will change greater not where the fan is but on where you pick the other in-flow window to be. this way you can selectively cool or warm other rooms without having a noisy fan in them. The second most important aspect is to block off any windows space around the fan. You want it to be a closed off system where the fan blows inside air OUT and there is no space in the window gap for the air to come back IN. Use towels, aluminum foil, pillows, anything you want so long as to block out the spaces around the fan. Use this fan and window system and anytime it’s at most 65°F outside you will be able to cool down your house to 70°F or lower quickly. And save much more power than if you were using the central AC. As a rule I never ever tun on the AC if it is in the 70’s outside. There’s no reason to.
These are some of the ways I save energy on heating and cooling costs of my apartment, but the most important takeaway is be flexible. Whether you feel it or not, the human body can tolerate a lot and will acclimate to much more than you are currently used to.