tl;dr: Why doesn't anyone make a variable speed split geothermal system with a COP over 5.0? I don't have geo, but I've been looking at various heating sources and what each costs to operate. Here in Connecticut, I have either had, or know someone who uses oil, gas, cordwood, wood pellets, air source heat pumps, propane, and electric baseboard. Basically, we have some of everything, not a lot of natural gas lines, and relatively high electric rates (they recently went DOWN to about $0.18/kwh). In my research, I have come to the conclusion that heat pumps of some type or cordwood are the most economically viable ways to generate some or all of the heat needed based on the fuel prices and equipment efficiency, which I have tabulated in a spreadsheet. In looking at heat pumps, I have looked at the following equipment as examples of high performing examples of each technology: Mini ASHP: Mitsubishi H2i Split ASHP: Carrier Greenspeed Geo packaged: Waterfurnace Series 7 Geo split: Carrier Infinity Geo hydronic: Climatemaster Tranquility Those are not necessarily the only high performing options for each type, but examples of equipment that performs near the top of the range of the available technology. Based on that conclusion, and the cost of installation, I can't see a way to justify putting ductwork into a house that doesn't already have it, or, in most situations, re-doing ductwork that is only suitable for heating in order to make it work for cooling. In these situations, it seems to me that the Mini ASHP is by far the most viable option in terms of cost and efficiency, with an existing gas, oil, or propane system running as supplemental if the Mini ASHP is smaller than <85% of the calculated design load, in which case, it would need assistance, and running as an offline backup that can be fired up if the Mini ASHP breaks when the Mini ASHP is 85% or larger of the calculated design load. Design calcs have a fudge factor, plus they assume grandma has the heat blasting at 70, when it's 2F outside in CT, so realistically, you can push things right to the edge with a heat pump if you have a backup system, say oil hot water baseboard. So this begs the question: why doesn't anyone make a Mini Geothermal HP, replacing the outdoor unit of a system like the Mitsubishi with a WSHP like a split WSHP system? Is there just a market mis-match between people who want a low up front cost, versus ones who want to spend the dough on a geo system? So my next musing is when you've got ductwork in a house already that is suitable for heat and AC. If your envelope is pretty tight with relatively small loads, and you've got a big zone of FHA fed from a furnace in the basement, great, packaged WSHP for you. Waterfurnace and Climatemaster have examples of all the latest technology of ECM fans, variable speed compressors, and everything put together putting out COPs in excess of 5.0. Here in CT, you've got to have a really, really good COP to justify the up front cost of geo at $0.18/kwh. You also have to size the system to carry nearly 100% of the design load, as electric strips running at $0.18/kwh are very, very painful, unless you have an oil or gas hot water system to fall back on. However, I can imagine a LOT of situations where a packaged WSHP isn't going to work, and a split WSHP is what you need: 1. Remote air handlers or furnaces. 2. Where it doesn't make sense to size the geo to design loads, but to use a furnace or hydronic coil for backup. 3. Houses with a bunch of air handlers running smaller zones. I have seen all of these situations, in houses that currently have gas furnaces or oil hydro air. There really isn't a good product for them to convert to geo right now. The split geo heat pumps that are out there today don't have the variable speed compressors and really high COPs that the packaged systems have, and are a really tough sell compared to a high end Split ASHP, like Carrier Greenspeed, which can be just plopped in place with a new furnace or ahu to give heat pump savings with hydronic or gas furnace backup heat. So my question is, why doesn't anyone make a high end variable-speed geothermal split system that can achieve a COP over 5? There shouldn't be any difference in the physics compared to a packaged system, other than the length of the refrigerant line. If they need a special fan or airflow configuration to make it work, they could build their own air handler with the option to put either a hydronic coil or electric strips in, as well as their own two-stage furnace with ECM blower. Further, this type of product should either be available in, or be able to be capped out in software to as small as 1.5 or 2 tons. This way, geothermal could be installed at a much lower up front cost, and still provide 90%+ of the heat to a building over the course of the season, with an oil or gas boiler or furnace doing back-up duty. I'm most surprised that Carrier hasn't staked this market out, as they have the Greenspeed/Evolution Extreme heat pumps, and the associated furnace and air handler line. If they transplanted the Greenspeed technology into the form factor of the Carrier Infinity WSHP, it would be a pretty unique, and very useful product for geo conversions.