Test your thermostat
Risk: If the temperature in your house isn’t what shows on the thermostat, your air conditioner or furnace could be working too hard.
How to DIY it: Every spring and fall, tape a household thermometer on the wall next to the thermostat. After about 15 minutes, compare readings. If the difference between the two numbers is more than a few degrees, try recalibrating your thermostat (follow the manufacturer’s instructions).
While you’re at it: If you don’t have a programmable thermostat, consider getting one. You can buy one for about $40 and install it yourself. It’s a relatively easy job; no rewiring required.
On the other hand, these are home improvement projects you should never DIY.