1. Field of the Invention
This invention relates to a fireplace, and more particularly to a solid fuel burning prefabricated fireplace construction adapted to be mounted in mobile homes.
2. Description of the Prior Art
The quality of mobile homes has, over the years, improved as a result of advances in fabricating techniques. In particular, these mobile homes have been made "tighter" due to better construction materials and techniques in assembling. Thus, the prevalence of minute openings from the inside of the mobile home to the exterior has been reduced in both number and size. Further, the addition of weather stripping, storm doors, storm windows and single sheets of wall ceiling and floor covering gives rise to mobile home units of exceptional air tightness.
In order to achieve an operational fireplace, the construction must be such that for each cubic foot of air carried away by a fireplace flue, an equal amount of air must enter into the fireplace opening. Of the air entering the fireplace, a portion must be made available at or near the base of the fuel so as to support proper combustion during the burning operation. This air, termed the "combustion air", facilitates burning by three distinct processes. Primary air must be present at the surface of the fuel to initiate the burning process. Secondary air must be present in the proximity of the flame to ignite with the gases generated by the primary combustion. Excess air must be available to blend with the products of combustion and become the vehicle by which the combustion products are carried off through the flue.
Fireplaces of conventional design are generally unfit for use in mobile homes. In particular, as a result of their exceptional tightness, these conventional fireplaces are unsafe to operate in mobile homes since the combustion air necessary to cause burning of the solid fuel is not continuously available to either support combustion or to carry away the products of combustion. Thus, while the solid fuel initially burns, after a brief time, the lack of combustion air results in a greatly retarded combustion. The ultimate result is a smoldering fuel surface emitting great clouds of toxic vapors and sparks. While normally such materials of retarded combustion would pass harmlessly through the flue and up the chimney, in the very "tight" configuration of mobile homes, an entirely different effect is observed. As a result of the warm air and products of combustion entering the flue, thermo syphon aspiration occurs and a slight reduction in pressure in the flue is produced.
Since there is no available make up air from the interior of the mobile home, this slight reduction in pressure is transmitted through the entire inside of the mobile home. Exhaust is therefore impossible. The ultimate result then is that the interior of the mobile home becomes dangerously filled with toxic vapors and sparks.
The only method found successful for the burning of solid fuels in conventional design fireplaces in mobile homes has, to this point, been accomplished by leaving a window or door ajar, thus permitting the entrance of exterior air for burning and carrying away the combustion materials.
It is generally recognized that fireplace modules designed for mounting in wall or window openings of existing building structures can most economically be produced if insulating material is kept to a minimum. The concept of a firebox housing separated from an outer wrapper housing by an air space has now been established as an alternate method of fireplace insulation. Cooling of the outer housing is readily accomplished by movement of either inside or exterior air between the walls of the outer wrapper housing and the firebox housing. For example, Northwood, U.S. Pat. No. 3,190,281 and Northwood et al., U.S. Pat. Nos. 3,049,113 and 3,123,063 provide for outside air to cool an annular space in fireplaces installed in existing building structures. While these fireplaces also provide for the entrance of outside air directly into the firebox housing, they would be completely ineffective for use in mobile homes since such air enters the top of the firebox housing, and above any burning solid fuel. The air would be clearly unavailable in the combustion process. Thus, as in the more conventionally designed fireplaces, the burning of solid fuel in fireplaces of this design would ultimately give rise to a fire that would be quickly retarded, emitting smoke and sparks into the interior of the mobile home.
A need exists therefore to provide a fireplace for mobile homes that is both efficient and safe.