Ok, so I've read five entire pages of threads here and as fascinating as it is, I am going to make myself stop and ask the questions that have come up as I've read the posts.  FYI, several of the links in the FAQs here, no longer work.

At present I have a 3 ton Reems Heat Pump.  The inside unit is 23 years old and the outside unit (our second one in 23 years) is about 13 years old.  My heat pump guy said that we will probably have to replace both inside and out this year.  He estimated the cost to be about $7,000. 

I decided to research my options before it becomes an emergency and I stumbled upon the Geothermal thing.

I had a Geothermal installer or designer? come out, he did a load calculation, measured my yard, blah blah blah.  The estimate is $25,000 for Water Furnace geothermal system using (1) 3 ton NDV038 Envision Series dual capacity unit with an ECM fan and a 10 year warranty  This does not include heater or humidifier.

I'll put my questions in separate threads for the convenience of others that look through the forum subject lines.

My question for this thread is:

Why do I keep seeing comments about back up systems and what will I do for a back up?

Thanks for any info!
Talking Dreams

Need for backup depends on where you live. If you are up north your system design will likely include heat strips - resistance electric coils as a very cold weather supplement / system backup. Your present system likely has the exact same thing.

Tell us where you live.

PS: BTW - your present system is likely a Rheem, not Reems (I'm an annoying stickler for details)

Wow 13 years on an ASHP, I'm impressed. I thought 10 years was the max for those things. My Goodman unit is 7 Years old, I'm toying with the idea of buying a replacement unit and leave it in the garage until the one I have goes. R-22 systems will be unavailable after next year and upgrading the entire system to R410A will be much more expensive than a $1,500 Compressor.  When you talking about the "Inside unit" I assume you referring to the Air handler inside the house and the compressor is outside.

Back up or auxiliary heaters mitigate the diminished returns of oversized geo systems by giving you the last few BTU's you need on extremely cold days in heating dominated climates. An extra hundred a year for auxiliary heat may save you a ground loop + 100's on the larger unit.
J

TechGromit,  you caused me to check my math.  Turns out that our first outside unit lasted 13 years (only because about 3 years in, the compressor failed and was replaced) and we have now had the third outside unit for 10 years.  Sorry about the misinformation.  I do remember being shocked when we had to replace unit ½.  The repair guy told me outside units are only expected to last 8 years.  I began to wonder if a heat pump was the most economical heating unit after all.  After some research, I determined that it was still the way to go, but EVERY EIGHT YEARS???

 

Joe, from your post I assume I need not concern myself with a back up unit?  Our last few winters have been very mild. 

 

Thanks to all in this thread for the very valuable information!

Talking Dreams

I think you'll still be able to get parts for R 22 systems in 2010 and beyond

R22 is in production 'till 2020 and replacement parts will be in production longer.
j

gosh - my Rheem 3.5 ton heat pump has been running for 20 years - only had to replace the fan motor about 10 years ago.

A backup system is that beeping sound you hear when you put your truck into reverse.

Oh you meant a backup Heating system. Usually your backup heat is electric resistance heat, expensive to run, but it really only should kick on if there's a problem with the geo system. Some systems use the electric resistance heat if they need little extra heat like when it's really cold outside, Like during an ice age. This way they can get away with a slightly smaller Geo system that would otherwise be required. It's installed inside the Geo unit, at the top where the air is forced into the house. Some people have asked if they should keep there old gas/oil/propane/coal/wood/fusion reactor heating system as a backup, but I think this is way overkill. A properly designed system will give you decades of trouble free operation. 
  

Can you please tell me what you mean by "save you a ground loop".If you turn the aux. off and it gets too cold will it do damage to the loop or to the heat pump because it would be running too much?

By installing a smaller system with a backup heater, you can not put as much pipe in the ground and thus "save a ground loop".

Running a heat all of the time will not hurt anything as long as the temp of the ground loop - EWT - does not get much below 30°. At EWT's of 25° most heat pumps will shut down and not run until the ground loop warms up.