I currently have a WaterFurnace Envision 5 series 5 ton unit that was installed when we built our home in 2009. It has two zones. Due to current code, one cannot put heat or cool into a garage and have the same returns come into the house due to the possibility of Co2 entering the house. With that said, I use a pellet stove to heat my garage, using approx 3 tons of pellets per heating season, average of about $600-800 each season. This adds up over the years, maybe I should be investing in some type of geothermal for the garage? Is there an application that can use my existing vertical ground loop and/or my existing 5 series to work for the attached garage without having returns into the home?