Yes it can.
Both the indoor and outdoor coils must be changed as well as the thermostat and possibly the thermostat wiring.
A modification must be made to the control wiring by installing an outdoor thermostat or a manual switch if you just want it for backup. An outdoor thermostat will prevent the gas heat from operating during mild winter time conditions.
The reason the contractor doesn’t want to do this is because it’s a field modification. There is probably equipment warranty issues involved as well. You’re furnace must also have a multi-speed blower that will produce the CFM required by the heat pump.
Just to have a backup may not justify the cost and modifications required to keep your old furnace around.
You can purchase the system you are describing in its entirety. There are called " dual -fuel heat pumps".
November 20, 2007
Dual Fuel Heat Pump System Become More Popular with Rising Fuel Costs
Analysis of: Conditions Raise Profile of Dual-Fuel | www.achrnews.com
This analysis is solely the work of the author. It has not been edited or endorsed by GLG.
Analysis By:Andrew Barton
Chief Executive Officer, CFM DISTRIBUTORS, INC
Implications: As fossil fuel costs rise more rapidly than electricity rates in many parts of the country, heat pumps sales have grown to a larger percentage of manufacturers outdoor unit sales than in years past. When heat pumps are combined with gas or oil fired furnaces, homeowners can choose the most cost effective fuel depending on outdoor temperature and utility rates. Increasing heat pump and dual-fuel system sales will increase manufacturers profits because heat pumps typically cost 20-30% more than air conditioners.
Analysis: In a challenging year for increasing unit sales, premium and dual-fuel (sometimes called hybrid) system sales are increasingly attractive to manufacturers, and channel partners because of the opportunity for increased profits. Every manufacturer can create a dual fuel system by combining their heat pump with their current gas furnace offering. Smart manufacturers like Trane, Carrier, York, and Lennox are creating additional options by offering packaged dual-fuel systems, and better marketing materials to help promote these systems.
Dual-fuel isn’t new, but it is easier than ever because most the wiring that used to be required in the field is built into a lot of new units. This saves contractors installation time and headaches. Awareness is increasing because of better marketing efforts on the part of manufacturers. While a dual-fuel system is often the best choice for homeowners when it comes to total cost of ownership, these systems still face the challenge of dealers effectively using the tools available to show the value of dual-fuel to end users. Look for dual-fuel system sales to help add to the already increasing percentage of heat pump sales.