Description of Prior Art
Insulation support bases for hot water tanks are known. In my U.S. application Ser. No. 826,603 entitled "Insulating Support Base for a Cylindrical Electrical Hot Water Tank", now U.S. Pat. No. 5,178,351 issued Jan. 12, 1993, I disclose the construction of an insulating support base formed of rigid insulating foam material whereby to support the bottom wall of the inner casing of a hot water tank and to facilitate centering of the outer casing thereabout. U.S. Pat. No. 5,180,077 also discloses a water heater bottom insulating disc wherein there is provided an upwardly convex center portion which mates with the concave base of the inner tank whereby to completely support the water heater and its water content. However, the center portion does not only support the inner tank, but at the same time, provides a better insulation than known prior art. These discs also permit centering of the inner casing and proper uniform spacing of the outer casing. Both these devices provide some thermal insulation to the base of the water heater.
In order to insulate the space between the inner casing side wall and the side wall of the outer casing, a sheet of insulating wool, such as Fiberglass.RTM. insulation, is usually folded over the entire inner casing from the top thereof and collapsed over the inner casing whereby to embrace the casing from both sides thereof. The insulating sheet may also be wrapped around the side wall of the water heater and a circular disc of insulation material placed on top of the heater. With these methods of insulation, it has been found that, in most cases, the insulating wool does not extend fully to the bottom of the casings and voids are created between the inner casing and outer casing adjacent the support disc spacing peripheral flange and elsewhere. Tests have shown that these voids in the side wall insulation results in heat loss in the tank bottom end and, therefore, energy inefficiency. By using expandable foam urethane much of the above disadvantages have been overcome. However, when using expandable urethane it is necessary to mask all crevices or holes in the outer casing and to introduce temporary plugs whereby to prevent expanded urethane to flow out of the outer casing or to obstruct areas where fittings need to be installed such as piping, etc.
Recently there was developed a need to recycle hot water tanks and at least the outer steel casing thereof. However, this was time consuming because the urethane foam had to be scrapped away from the inside wall of the inner casing. The use of plastic sheet wrappers was developed to solve this problem whereby the wrappers would protect the inside wall of the outer casing to prevent the expanded foam to adhere thereto. My U.S. Pat. No. 5,178,351, discusses such a wrapper and related prior art. The wrappers are formed of plastic film material and have one major disadvantage, that being that when the hot urethane is injected therein the wrapper bursts or melts due to the excessive heat of the liquid urethane which exceeds beyond the melting point of the wrapper and some of the urethane flange between the wrapper and the inner tank wall and between the wrapper and the outer casing at the base portion of the wrapper. As the foam quickly expands it quickly flows out of the outer casing through the gaps existing around the pipe fittings and the outer casing. Up to 50-60% of the material can escape through these gaps and when this happens the hot water tank is rendered unusable and needs to be recycled. This is very time consuming and costly.
It is also well known in the art that bacteria contamination of water in hot water heaters is susceptible in the lower end of the hot water heater where the temperature of the water is at its lowest. This phenomena is clearly described in Canadian Patent 2,030,976 issued on May 29, 1992 to Hydro Quebec and there is a brief description in that patent of the need to maintain the water temperature as high as possible in the lower tank region. However, this has proven difficult. It is therefore essential that the lower portion of the tank be properly insulated and this has been heretofore difficult to achieve due to the insulating methods utilized during the fabrication of hot water heaters. Reference is made to my Canadian Patent Application serial No. 2092348 published on Sep. 25, 1994 where I discuss this problem and present a solution but limited to the use of Fiberglass.RTM. wool