background: I am preparing to build a ~4000 sq ft in Western Washington state (moderate climate). I am leaning toward a Warmboard-based, radiant floor heating system with an add-on AC system (yeah, the AC is a luxury in this area, I know). The site is rural, so I figured I'd end up with propane-powered heating (boiler), and an electric AC compressor. I was talking with a contractor today and he suggested that I consider a (reverse?) chiller for both heating & colling purposes, and that chillers are efficient and well-suited for our moderate climate. Further explanation described it as a "air-to-water" heat exchangeer, as opposed to a "air-to-air" heat exchange, aka what most people today call a "heat pump". A couple of brand-names were mentioned as well - Multiaqua and Unichiller. I've since found Aqua Products as well. The contractor is a reputable one here in our area, and I'm sure he's not trying to steer me wrong. I'm very puzzled though why I haven't seen more discussion of chillers on forums like this one, if these things are so great? thx, Jay

Check out the Radiant Panel Association's discussion forum. Many of the top radiant industry experts hang out there and they do discuss reverse chillers.

http://radnet.groupee.net/eve/forums/a/tpc/f/4771065301/m/4971036643

I'm not sure which contractor you are talking with, but one that I know of that is quite technically savvy is Josh Mitchell at Mitchell Mechanical.

http://www.mitchell-mechanical.com

Thank you Barry, I appreciate the link. Based on the comments I've seen so far, reverse chillers seem to be relatively new on the residential scene but have some appealing benefits (allegedly, a COP that approaches that of geo-thermal heat pumps).

We are working on a 6,000 sq ft house right now in Seattle where we are designing the heat side to a meet a leed's gold standard. Initially we had called 2 reverse cycle chillers in the spec. We needed 2 5 ton units for 6,000 sq ft, in this region.
We have pex pipe in all in 4 floors and a Hi-V air on the top 2 floors for supplemental cooling, air filtration and Heat recovery ventilator (HRV) and air movement. We have since modified the design to 1 conventional 5 ton heat pump for the forced air side and 200,000 BTU condensing boiler pack with side arm tank to cover the in floor and domestic H20. Reason being both appliances are straight forward for future service work. The single 5 ton Heat pump can offer some back up should the boiler unit go down, further we can temper the building at the same traditional low cost heat pumps enjoy. Domestic h20 production is significantly increased provided by the boiler, and as condensing boiler can be held to a low delivered H20 temp, fuel efficiency can increase.
That said the reverse cycle heat pumps coming out are comparable to the geo systems, some back up will be required in this climate for degree days less than 32. That can be accomplished with an 80 gallon commercial electric water heater used as the buffer tank.
Dan