I plan to put a geothermal system in my 1973 ranch style, about 1200 sq ft with full basement, central Illinois.  Presently have electric ceiling heat strips and an ancient (25 yr) central air.  Have a bid from WaterFurnace for Envision ND038 3 ton unit and bid for GeoComfort GT036 3 ton.  Are these systems comparable or is one more reliable, efficient than the other?  There is about a $2600 difference between the bids.  Also the WF guy estimated heat load at 58,282 btuh while GC guy estimated heat load at 30459 btuh.  Is this a concern?  Both systems include hot water assist. 

I'm not too familiar with the specific models you mention, but the heat load difference is a concern. You need to understand where these 2 numbers come from. Are they the amount of BTU's required to heat your home (output of the heating system) or the btu's required as input of the heating system? If they are the btu's required for input to the different systems, there is a mighty big difference. If they are the output BTU's, that is still a pretty big difference, but would depend on the efficiencies of each system. I did notice that both units are 3 ton units, so they do seem to agree on the amount of cooling you need.

In either case, Ask to see the J Calculations (heat loss calculations). If neither bidder gave you one, or is unwilling to give you one, find another contractor who will. Anyone just figuring in their head what your house needs might be right...but there is a lot of room to be wrong. I have dealt with a few contractors that tried to give us the "square footage" rule of thumb. For every x square ft you need y amount of heating. Problem with this is that it doesn't take into account any factor that would maintain or release heat from your home (insulation). The assumption is that your insulation is just as good as the other homes these contractors have worked on. Let the numbers and the calculations guide you to what you need, rather than what someone wants to sell you. In the end, you will end up with a product that best suits your home, and the regret factor will have nothing to do with the product (and you might be pleasantly surprised if your home fares better in the insulation department than a house with similar square footage, but less insulation, which could result in needing a smaller system)

Where are you at in Central IL? One of my friends does the field work for geothermal systems. I am not in these trades myself, but am an engineer, so him and I often discuss his work. Feel free to call him up.

Mark Layten
Kickapoo Drilling 405 W Main - Downs, IL 61736 ph: 309.378.4003 fax:309.378.4099
www.kickapoodrilling.com/aboutus.nxg

They are also listed as members of the Geothermal Alliance of Illinois, where the head of Kickapoo Drilling (Jim Layten) is on the committee for training and certification.

I have talked to both contractors in the last couple of days and both say they have used manual J to do their calculations. They did both sketch out the house and check out the insulation and windows. I don't know if the difference is from the software they used or if they started with different assumptions. They said they would send copies. Both have done a lot of geothermal installations so they would appear to know what they are doing. A friend who works for my electric coop says they have had no issues with either of them. Right now the Geocomfort is prefered in my mind on price since as far as I can tell there is no significant difference in performance. Thank you for your input.