Depends on what equipment you have - air handler and thermostat. Also, the coil is usually placed before the fan in an all electric system and after the fan/heat exchanger in a gas heat/AC system. It get a little murky if you use gas a backup heat - ideally, you would want to disable the heatpump when the gas backup kicks in.

Ramon what you posted sounds like a crock but here's a much cheaper solution. Have contractor A connect present t-stat and a new outdoor sensor to run heat pump until weather become's too cold then switch to back up coil heat. If existing coil doesn't supply ample heat,add another coil string to the handler,it's routinly done all the time. There is no reason under the sun to have propane as a third stage if you don't want propane. Besides,you are not getting propane with contractor B. I still say the whole story smells but there's how it can be done just the same. Just for the record,I've never seen resistance heat in combo with gas heat but it would be easy done so I wouldn't say it hasn't been.

From my reading on this and other forums, homes with heat pumps in cold areas always have a secondary heat source for when outside temps drop to a point where the heat pump can't produce enough heat. The secondary source can be electric resistance (electric heat strips) or a furnace using whatever is available - natural gas, propane, oil. A furnace is usually after the coils in the return air path and if the furnace is on, the return air simply passes through the air handler with a coil that's neither cold (as in AC mode) or hot (as in heat pump mode). This is normal and no problem. Same is true of a house with an AC coil and a furnace, that's what I have.

What contractor A is saying seems closer to good advice. Unless you have very inexpensive electricity, using the propane furnace may be cheaper than using the resistance heat. But maybe not. In either event, having an outside sensor to determine when the low temperature is reached, and so requiring a switch to the secondary heat source (whatever you decide it is), is the normal thing to have.

Thanks everyone for there comments! Right now what I currently have is:

- Heat Pump: HEIL Model NXH536GKA100

- Furnace: ICP (International Comfort Products) Model END4X36L17A1

Right now the system is set up to use the heat pump as our primary heat and when it gets too cold, the furnace would kick-in as the secondary source of heat. The furnace does not heat up since the gas is disconnected right now. My question was whether it would be possible to add the electric coil as THIRD source of heat. Or more specifically, Heat Pump would be first, followed by the electric coil and then the furnace. This would allow us to keep the gas but use it a much lower rate (only when it gets REALLY cold) as we would be mostly using the electric coil.

Contractor A's proposal involved putting in a new thermostat and an outdoor sensor. When it gets too cold that the heat pump can't handle it, the electric coil would kick in and the outdoor sensor would trigger the furnace if it gets even colder. Still, it would be something about 80% coil and the remaining 20% furnace. The way he said it, it seemed that there already is an electric coil on the inside of the house, it just is not wired-in to be used. I have no idea what to look for so I have no idea he is right or not.

Ramon you should find another hobby because attempting to BS people on the net is making you look pitifully foolish.

I don't now how exactly I'm bsing people, klem1. But since you appear to believe that's what I'm doing you can just ignore my questions and let people willing to inform me answer instead.

For everyone else, these are genuine questions I have because of what the first contractor told me.

I'm not familiar with HVAC systems at all and want to be informed so that I'm not taken advantage of.

Thanks sktn77a.

So there's supposed to be one there but there isn't? Can one be added?

Or are my options to just change the air handler or the HVAC system?

Ramon,

If the heat pump is working properly and it is correctly sized it will be able to provide enough heat with either electric or propane back up. This will be true up to an outside temperature. Below that temperature you need a back up source of heat.

If you know what you are paying for electricity and propane then you can calculate which option would be cheaper to operate. Posts the rates and someone can do a calculation for you. You will also need the efficiency rating of the furnace.

What you have is an upflow (blower blowing up through the gas heat exchanger). The only way you can add electric is to install a separate cabinet approved to hold the coils safely. You cant just shove coils in there somewhere safely.

Or you can install an electric plenum heater.

More discussion

http://hvac-talk.com/vbb/showthread.php?714771-Retrofiting-heat-strips-element-in-existing-gas-furnace

Electric plenum heater as noted by Chuck on the last post

http://www.electromn.com/pdf/EL703.pdf

Personally I feel the electric plenum heater would be your best bet.