a/c with propane to heat pump

ive called 2 local contractors and told this cant be done

currently have a york a/c condensor 5 ton 10 seer unit
and a diamond 80 furnace.

i would like to change out the condensor for a heat pump but keep the propane as backup heat.

can this be done?

thanks for any assistance

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.

I agree with David yes it can be done, not rocket science your contractors would probally like to sell a complete system rather than modify and yes it will require some special wiring that your contractors may or may not know how to do or just don’t want to.

I have dual fuel in my current home and in my last. (Both new construction) Totally sold on dual fuel. Two homes before that had oil hot air and A/C and were OK, but I wouldn’t go back. In considering a retro fit, carefully scrutinize your goals. Look at costs, benefits and payback period. My heat pumps work above 38 degrees. Below that I’m burning propane (90+ furnaces). Comfort level and economy are great. If your current furnace is an 80% or less (metal flue), consider the whole new system, it will work better together. Or consider a whole new house - recommended ( builders need work too).:slight_smile:
Rick Fifield

The biggest problem with the heat pump versus a dual fuel is the defrost cycle.

The heat pump runs for about 45 minutes and then a timer on the circuit board checks to see if there is ice on the coil outdoors. If you live in the mid-south or areas where it gets warm during the day and very cold at night you have a very high humidity content in the air and ice rapidly forms in the coil ,which must be 30° below the outdoor temperature to adequately absorb heat. Obviously, it freezes up within minutes/seconds of operation. During the defrost cycle electric heaters come on (major amperage draw), the outdoor fan shuts off to expedite the defrost process and the unit switches over to air-conditioning, absorbing a large percentage of the heat that was produced over the last 45 minutes to defrost ice on the outdoor coil. It takes almost a thousand BTUs per pound to change ice to water. After the ice is gone the outdoor sensor turns the unit back to the heat pump mode so that the outdoor coil can again freeze within minutes/seconds and continue to run for the remainder of the 45 minutes. No air through the outdoor coil results in no heat absorption and the interior of the home cools down, causing the auxiliary heat strips to come back on.

To make things more uncomfortable, the indoor fan never shuts off, even when the auxiliary heat has satisfied the indoor temperature setpoint. This blows cool air and the air movement reduces the insulation effect of air around your body.

A dual fuel eliminates this air-conditioning/defrost cycle when it is most objectionable (when it’s very cold outside).