Determine if you want to convert the entire house to central heat and air or if you would like limit the conversion to the most trafficked rooms. It will be significantly more expensive to convert every room in the house.
Choose the location for your unit. It must be centrally located to reduce ductwork, materials and labor cost.
Measure from the central location to the rooms the unit will service.
Obtain the price of installing the central unit and all of the ductwork and construction. Factor in any of the labor that you can do yourself. This will be the labor cost for the conversion to central heat and air.
Price the materials you will need to convert the house to central heat and air. The materials will include the central unit, the ductwork, vents and miscellaneous material. You can call a local heating and air-conditioning company to obtain the pricing information for these materials or price the materials on the Internet (see Resources below).
Add the labor cost and material cost together to calculate the total costs of converting a house to central heat and air.