We are getting ready to install a geothermal heat pump and have gotten two quotes from local reputable contractors. The differences in the two quotes were primarily in the recommendation for which unit to install. One contractor recommended a Series 7 and the other recommended a series 5. The price difference is about $3800. A few facts: - we are in suburban Washington, DC - we are in a five level split house approximately 3500 square feet - both units recommended are 4 ton - the unit will be located next to our family room in our basement - we have hot and cold spots in our house and may install a zoning system later but it's not an option now We want to make the best decision for the long run but don't want to waste money. Any recommendations are appreciated along with rationale.