A single-stage furnace is the simplest and most affordable high-efficiency option. It fires at 100% every time it turns on, then shuts off once your home reaches the set temperature. That keeps upfront costs low and service simple, but it can cause noticeable hot and cold swings and louder start-ups. Find out whether a single-stage furnace is the right fit for your condo, townhome, bungalow or rental property in Calgary. The guide also covers when upgrading to two-stage makes more sense.