For years Kenneth Darby burned household waste in a trash barrel down at the bottom of the yard and thought nothing of it; that is, until energy costs skyrocketed.
Then four years ago, as he watched his trash-barrel furnace burn away for the better part of two hours, he agonized over all those wasted Btu. Wouldn't it be great to get all that lost heat indoors, he thought.
As an engineer, he was better equipped than most people to translate an idle thought into a practical reality -- so he went to his drawing board. What he came up with was an outdoor furnace that burns both trash and wood (it can be adapted for coal), providing hot-water or hot-air heat to the home along with domestic hot water.
Three years ago Mr. Darby built his first experimental unit in his backyard. Improvements have been made since then, but the original furnace still performs so well that he is loath to pull it down. The inventor calls his outdoor furnace the HAHSA. No, it's not Swedish, as some believe. The acronym stands simply for heat and heat storage apparatus.
These are some of its immediate advantages:
* Efficiency. Because of the tremendous heat storage (thermal mass) that comes with the design, the fire can burn at full capacity, extracting the maximum number of Btu (units of heat) from the fuel.As a result, it burns less wood than a stove for the amount of heat it provides. Moreover, it can burn pine logs as well as hardwoods, and even freshly cut green wood. It will also burn household trash. One Midwesterner fuels his unit with "dirt cheap" corncobs, readily available in his area.
What Mr. Darby calls a HAHSA bag is simply a supermarket grocery bag which is the receptacle in his kitchen for combustible household waste -- paper, old magazines, old dustcloths, plastic bottles, and the like. When full, it is included with the more conventional fuels at the next firing of the HAHSA.
* Economy. Not only are some of its fuels ----tic hot water as well as space heat to the home. Mr. Darby's unit heats his 2,100-square-foot home and provides hot water for a family of seven on about five cords of wood a year. His electric bill, which included both heat and hot water in pre-HAHSA days, used to run out at $145 a month. Now it comes in at around $45 in this corner of Pennsylvania.
* Safety. Unlike a wood stove, the HAHSA is outside in the backyard looking rather like a garden tool shed. Thus, the threat of fire from overheating is nonexistent. Nor is oxygen depletion ever a threat. A North Carolina nursing home that added a HAHSA to its existing heat system stressed safety as the deciding factor.
* Cleanliness. The same factors that make the HAHSA safe also make it clean. Ashes stay outdoors and termites or other insects stay there, too, because no fuel from the woodpile ever comes indoors.
* Simplicity. The system ties in directly with hot-water radiators, baseboard hot water, or, with a heat exchanger, to hot-air systems.
* Carefree. There is no need to constantly tend the fire. On the most bitter of winter days, two firings might be necessary. Otherwise, a once-a-day firing is all that is needed, and even less often in the fall and spring. In summer, domestic hot water can be provided on two firings a week because of the impressive heat-storage capacity.
* Neatness. The exterior of a HAHSA unit is generally built of concrete blocks which can be painted. In many cases it can be clad with siding that matches the house.
The system might best be described this way: A firebox is surrounded by several square yards of sand, which, in turn, is held in place by the shed building. embedded in the sand are 1,100 feet of plastic pipes connected to the home heating system and 250 feet of copper piping (placed nearer to the firebox) for the domestic hot-water system.
The fire, very simply, heats up the sand, which then transfers its heat to the water circulating through the pipes. Water temperatures range from around 95 degrees F. to 130 degrees.
The HAHSA is basically designed for the average US home that is moderately insulated and with up to 3,000 square feet of living space. A large and leaky farmhouse would require some backup heating system for very cold weather, Mr. Darby says.
In nearby West Wyoming, Pa., Dr. Robert Bishop built a HAHSA to serve his 4, 000-square-foot animal hospital. The building, not as well insulated as more modern structures, gets 70 percent of its heat from the HAHSA, but a backup oil system is necessary. Even so, Dr. Bishop calculates his unit will have saved him $2,200 in fuel oil by the time the current heating season is over.
There are some 500 HAHSA units in operation around the country, all the result of people buying plans from Mr. Darby ($20 from HAHSA, PO Box 112, Falls, Pa. 18615).
At current prices for materials, a do-it-yourselfer could probably build a HAHSA for $1,800, but buying ready-made components from Mr. Darby would increase the price to around $3,400. A general contractor could build one for about $4, 500, using Darby-built components.