I am a builder a SW missouri and a customer is wanting a heat pump.  On one website they briefly mentioned being able to place the coil underneath the house.  Has anyone ever done this or have any advice on it?  We are trying to make the system as cost effective as possible and we already will be below the frost line, etc.

Hi, Welcome to the forums.

If you are doing a horizontal loop, there is not enough room under the house.

If you are doing a vertical loop, then you have to pull the drill down into the basement which would be more hassle than it is worth.

How much room is needed?  What is the most "cost effective" approach to doing geotherms?

EarthLinked DX is usually the most cost effective. When doing vertical, the loops are spaced 7' apart. If the mean earth temperature you have is higher than 55 deg. F., then you'll need at least 1.5 loops per ton, 100' deep.

If there is room for this, then you just have to schedule the driller. Typically, though, drillers are too busy to meet that kind of schedule. We did our second one just this week where we put the loop inside the structure. Both times we've done this, the builder has bigger expectations than he should, and he thinks we hold up the project. Drilling takes time. Sometimes I can get 4 holes done in a day, sometimes only 1. It depends on the drilling conditions.

The savings you might see with putting it inside the structure are only in the range of about $500, maybe $800. To me, it's not worth being blamed for holding up the project.

Oh, just to clarify, the 1.5 loops per ton would be like you'd need 6 holes, 100' deep, for a 4 ton system.

That would be a lot of holes for this home, it is about a 5700sf home, 3k up and 2700 down.  So the number of tons needed would be pretty large.  With these systems can you figure tonage similar to a typical unit?

Depending on the insulation, window types, ceiling heights, etc... basically based on the load calculations, we can then figure tonnage. My dad's home is an ICF home, basement to roof. It's about 5,400 sq. ft. He heats it with a 5 ton EarthLinked system. However, we're in Utah. We size to the heating load here. In your neck of the woods, you may size to the cooling load. But just as I said before, with your loads (heat loss BTUh, total heat gain BTUh, and sensible heat gain BTUh) the tonnage can be figured.