Has anyone had experience with geothermal paired with radiant floor instead of a forced air heating system? I may be doing a deep retrofit of a 40 year old house in climate zone 6. Minimal air conditioning requirements which I think can be easily handled with a 3 or 4 zone mini-split system. Square footage of this house is about 3,000.

House is on a natural gas line. Is it cheaper to just get a high efficiency boiler and an indirect water heater? Or would this be a good idea to look into getting a geothermal system? We want to do radiant in floor heating as we're tearing out all of the floors and this is a perfect opportunity. There's currently no air conditioner, but the climate doesn't really require it except for a handful of humid days during the summer (which we could can take care of with a 3 or 4 minisplits off of 1 condenser).

Any fossil fuel that is available cheaply is usually a deal breaker when compared to anything else. Geo works well for water to water. The advantage geo would have is that a combo unit could be purchased and provide water to water for heat, and water to air for air conditioning. Giving you one system to service and maintain. Do your homework locally as prices and applications vary wildly by market.
Eric

Given current and forecast low natural gas prices, I would stick with that and your mini-split heat pumps for cooling and possible heating in the shoulder seasons when temps are not extreme.

With natural gas available, in my market area the tax credit which would cover process piping could make recapture of additional investment in geo attainable inside of 10 years. You want to take a hard look at the numbers to make sure it's the right way for you.
I do want to mention, while people often squawk about the inadequacies of geo warranties, you are not likely to find standard warranties on modulating boilers half as comprehensive and the parts for these things which are mostly OEM are not cheap.
Finally ask to see references for radiant projects. Good geo guys are way more common than good geo radiant guys.
good luck,
joe