I have a two speed Waterfurnace GeoThermal that is approaching 20 years old. It ran without any maintenance other than sir filters for about 15 years, then in the next couple of years I had to replace the three speed forced air fan (for which WF could not produce an exact replacement so I had to pay extra to retro fit a newer unit) at about $1,200. Then a couple of years later I had to replace the two ground loop circulation pumps (this had some misdiagnosis problems - I'm a retired electrical engineer or these errors would have gone unnoticed) at an additional $1,500 or so (I would have to look up the cost is anyone wants to do a financial analysis). Still given the amortized cost of repairs over 20 years is about $120 per year, no more than what an oil furnace tune up cost - I guess - not a big issue. But, what next, the compressor? As you know the whole unit, other than the loop, is inside the house so a replacement of the compressor doesn't leave me with a rusted housing, the unit look new (to my old eyes at least). I seek any advice on when one should consider the unit about ready to fail, and the best approach forward, including replacing the complete inside equipment - maybe with a variable speed compressor which I think is a giant step forward in reliability, regardless of the fact my two speed compressor is still running about about 20 years. It looks like new designs, even two speed, can give me a significant improvement in efficiency. In low speed my unit delivers a COP of about 4.0, a newer design may give me 5.0 or even better, but at what cost? I think I can not retrofit an upgraded compressor in my existing unit (I can provide the model number is any interest is generated), but if I can that would be another consideration. I think the installer of my Waterfurnace did a super job, a real crafstman. But, he has changed form Waterfurnace to Climatemaster... suppose I can change there too, the ground loop doesn't care and I'm sure both make a unit that fits my available space. 20 Years go I paid about $12,000 for my Geothermal, I estimate a similar installation today would run over $25,000. But, I have a ground loop so it may be I can get a replacement furnace and pumps for under $15,000. Am I anywhere in the ballpark on these estimates? I will contact local (not real local as I live in a rural area) contractors to get a price/bid, but will appreciate some insights from others first. Hope my unit doesn't fail while I'm making a study. That will bring the whole subject to an emergency answer, not the best way to go. I'm new here, but not new to residential geoghermal heating and cooling (hot water is another story - that too has improved in the past 20 years).