The cost of a standard efficiency gas furnace with installation starts at $2800 and a high efficiency gas furnace starts at $3800. This includes a standard installation with no extras. Any code upgrades or additional work such as new duct-work are extra. If you are wondering what the biggest factor is in the cost of a furnace it is the brand. We can help you choose the best furnace for your situation when you give us a call. We offer financing on furnaces through Service Finance Company, LLC.