| hickory I have Geothermal as well and just finished installing a whole house ERV myself. I did mine for around $1100 includinbg all parts - I hope this helps you out. My house has 3 GT heat pumps. Two in the basement and one on the second floor. The second floor suite has guest BR's that we almost never use. The basement and main level are large - around 3900 sq feet each. The main floor has the main living areas plus our master bedroom and bathroom. One of the GT units in the basement services the master suite and the basement area below it. The second GT unit in the basement services the main living areas and the basement area below it. The basement is partially finished but I had the HVAC ducts run down there in preparation for completely finishing it. So there are 2 large returns (one for each GT unit) for handling the basement spaces and then there are multiple returns on the main level too. This duct set up was key to how and why I did the ERV the way I did. The ERV unit I purchased was a Broan whole house unit with HEPA filter. At maximum speed it is spec'd to handle around 6000 square feet. I decided to simply add this unit in the basement in a standalone configuration. One reason I love the Broan is that they have a special connector for the outside penetration where one 6 inch hole handles both intake and exhaust. Since I was drilling and cutting through a stone veneer exterior, I only wanted to make one hole. For the ERV stale air draw from the house, I connected an 8 inch duct from the ERV to one of the large return ducts servicing the a large room on the main floor - the library - and for that return I had easy access to from the basement. The ERV conditioned fresh air dumps into the basement. I let the thermostats on the main level (Honeywell IAQ Vision Pro) cycle the air from the basement to the main level and vs. versa. I programmed these tstats for Ventilation and with my house settings, the HVAC fans come on for about 20 minutes per hour. Because of the way my house is ducted, i get good air flow between the basement and main floor. Hence the fresh air from the ERV dumping into the basement easily makes it's way upstairs to the main level. The ERV runs all the time during mild months and draws about 225 watts in max mode. During the peaks winter and summer months, i plan to run the ERV in Auto Mode - see description below. I did not wire the ERV to the Vision Pro tstat even though this would have been very easy. The Vision Pro has a dry contact relay for controlling an ERV. When you program the Vision Pro for an ERV, you can tell the HVAC fans to come on and the dry contacts on the tstat will close. If your ERV has a dry contact relay control input (or if you add and extrnal relay in), you can have the VP tstat turn the ERV on and off. The reason I did not connect the ERV to the tstat is that the Broan unit has it's own controller with some features that I really wanted, but that the Vision Pro tstat does not have. Had I connected the ERV to the tstat, I would have had to bypass the Broan controller. The Broan controller has an Auto Mode that has two temperature settings that I wanted to handle extreme conditions (hot or cold). The unit has it's own internal thermotstat that measures the outside air temperature coming into the house. When in Auto Mode, if the temperature is below a the Low set temp or above the High set temp, the unit will close the fresh air input and just circulate air inside the house. I really wanted this feature because when it gets very cold out or very hot and humid, I would rather not have that ERV blowing this fresh air this into my home and potentially overwhelming my GT system (or causing my aux heat to come on). So I think it is possible to have 1 ERV unit handle your house but you need to consider the house design, how it is ducted, and how the house will be lived in. I purchased my unit from www.iaqsource.com and they offered free shipping on the Broan units. They also have a nice tutorial on the site that explains ERV's and HRV's and the temp zones recommended for each. It took me a few hours to hook it up - most of that time was cutting the 6" hole through the back wall of my house. I am very happy with the unit and only wish I had installed it sooner. My house is well insulated and sealed and during the months when we have windows always closed, you could tell that we needed a fresh air supply. Good luck. | 
