Wish I could find the picture to post, but it's gone...
When I installed my geothermal in November of 2010, the contractor who did the duct work for upstairs was way behind schedule and it was getting cold...
I took a 6 cu. ft. packing box and shoved it between the top of the geothermal unit and the bottom of the old ductwork that fed downstairs, turned the pump on and heated the main floor of the house for nearly 2 weeks!
JQ