| Number | Name | Date | Kind |
|---|---|---|---|
| 3201948 | Schramm | Aug 1965 | |
| 3471953 | Wyatt | Oct 1969 | |
| 3575006 | Rugroden et al. | Mar 1971 | |
| 3583168 | Harton | Jun 1971 | |
| 3851489 | Richardson | Dec 1974 | |
| 3948059 | Pampa | Apr 1976 | |
| 4332511 | Bradley et al. | Jan 1982 | |
| 4650370 | Kassner et al. | Mar 1987 |
| Number | Date | Country |
|---|---|---|
| 410900 | May 1934 | GBX |
| Entry |
|---|
| Publication by the Charles Machine Works, Inc. entitled "Ditch Witch 6510" dated Jul. 1986. |
| Publication by the Charles Machine Works, Inc. entitled "Earth-Coupled Water Source Heat Pump" dated Sep. 1987. |
| Publication by the Charles Machine Works, Inc. entitled "Earth-Coupled Water Source Heat Pump" dated Sep. 1987. |