Installing new heat pump with existing furnace

[wlmoss]

Need to replace a 21 yr old Trane 3-Ton heat pump & have no knowledge on heat pump sytems. I have several quotes, however am receiving conflicting info regarding the compatability of the new unit with our exitsing furnace(also 21 yr old Trane). I need enough info to determine if what I'm being told is legitimate advise or a sales ploy.

The quotes are based on a Trane XB13 & XR14; Lennox XP13A-36, and a low-end/construction grade Rheem13. Other than replacing the inside coils to be compatabile with the new unit, any other reasons why the existing furnace would not work with the new unit? I have been told the new unit will not be as efficient with the old furnace. Am willing to deal with that provided, it will heat/cool/dehumidify the house as well as the old unit. Besides, I feel any of the new units will be more efficient than the one being replaced.

Of couse, this was not budgeted. Quotes range from $3500 for Rheem/Lennox (5yr compressor warranty) to $4200 for Trane XR14 (10yr) or $1900 repair job for new compressor & coils (1yr). Any info to help me not waste money would be greatly appreciated.

[Brian E. Kelly]

SEER ratings have changed in Jan. The new units are more energy efficient and my not be compatible with the older unit. I would consider replacing the whole 21 yr old system myself.

http://www.aceee.org/consumerguide/topcac.htm

[Bruce A. King]

I agree, even if it was only 12 years old, replace all of it.

[Larry Ewens]

Were I you and had a furnace I wouldn't worry about a heat pump and just install an AC unit and let the furnace take care of the heat aspect of it. It would most likely be cheaper that way also.
Larry

[Eric P. Kravitz]

My top 5 reasons for a full system upgrade...

1. average life of a gas furnace is 18 years; it's on borrowed time right now.
2. would be less expensive in the long run installation-wise to change the complete system all at once rather than have to disconnect the evaporator at a later time to just replace the furnace.
3. new HP system will work with old furnace, it will just not work as well as it could.
4. with the new variable speed blowers, you could possibly get 15 SEER out of that 14 SEER unit
5. IAQ - look into high eff. air filtration, humidification and UV air treatment. these are the best things you can do for a home and a family when considering a new indoor comfort system.

[Mark A. Timpani]

Eric, very good info

[jrupert]

All of the units you listed 13 SEER models and require the indoor coil to be matched to the new unit to achieve the rated higher efficiency and to enforce the manufacture warranty which will be voided if the coil is not changed.

The reason to replace the furnace is due to airflow reasons. The newer furnaces are matched to provide the proper air flow (proper ducting is separate issue) to ensure that the new 13 seer system works properly. The new systems DO NOT have the tolerance that the older units had for poor air flow, improper sizing, over charge of refrigerant.

If your old furnace can not provide the air flow, the compressor may fail, the unit will not cool properly and bills will be high.

All the units you mentioned use the same installation requirements no matter the manufacture, including the unit you mention as construction grade, which by the way Rheem would not agree with that statement

The addition of the heat pump to a gas furnace (duel fuel system) will give you the best fuel savings, in most parts of the USA the heat pump will beat hands down the cost to produce heat then even the high efficiency gas furnaces on days when the out door air is above 40 degrees

Also have your ducting inspected, if it can not flow the proper air, then your back to step one, also replace the copper lineset, and install energy efficiency thermostat.