6 Low Cost Ways to Save Replace or clean furnace filters every one to three months. Dirty filters restrict airflow and increase energy use. Keeping your furnace clean, lubricated and properly adjusted will reduce energy use, saving up to 5 percent of heating costs. In summer, keep central A/C condenser clear of leaves, bushes, etc. Use a ceiling fan and turn up the thermostat a few degrees. Do not simply remove dirty filters. This will allow dirt to collect on the heat exchanger surfaces and reduce efficiency.