Furnaces and houses share a symbiotic relationship—the furnace supplies the house with heat, and the house supplies the furnace with protection from gangs of snowmen. Keep the heat on with today's Groupon: for $79, you get a furnace tune-up (a $140 value) and water testing (a $50 value) from Harker Heating & Cooling. Today's Groupon is only valid within their service area of Dane County.

During a furnace maintenance visit, Harker Heating & Cooling's specialists give homes' heating units a thorough examination. Components slated for inspection include the thermostat, blower assembly, air filter, vents, electrical connections, and safeties. Pilot lights, heat exchanges, and burners receive a careful cleaning to remove excess dust or illegal Greek fire. To improve the furnace's efficiency, a technician will lubricate chafed motors and bearings with a spritz of oil. After checking for gas leaks or evidence of carbon monoxide, Harker's staffers test the water and run the furnace through a complete cycle to ensure that it's ready for another prolonged struggle with Old Man Winter.