You'll like this new outside heating system that uses a 1,500-gal. reservoir of water to store heat.

The new GARN outside furnace is state-of-the-art wood burning, with an airtight firebox that burns so efficiently it doesn't have a chimney. Air exhausted from the firebox contains little smoke or ash when properly dried firewood is used.

The furnace is designed to be placed outside in a shed, garage or barn and can be used to heat buildings up to 500 ft. away through insulated underground pipes. A tightly insulated box is constructed on site around the firebox and its water jacket, which contains 1,500 gal. of water. Just 2 to 3 hrs. of burning in the stove brings the water up to about 200 degrees, which is enough stored warmth to heat the average-sized home for 2 to 3 days in the dead of winter.

"It can be centrally located on a farm and piped to the house, barn or other locations," says Jeffrey Anderson, GARN representative, noting that one hog farmer -- Tom Lawton, Ellsworth, Wis. -- recently installed a GARN system to replace two 60,000 btu propane heaters in his farrowing house and a wood heater that used about 7 cords of wood in an average winter to heat his house. Lawton now uses only the GARN system and says that he expects to use just 10 to 12 cords of wood for the entire winter.

The GARN system easily connects with existing heating systems. In forced air systems, a radiator-like heat unit is simply mounted in the forced air ductwork. For hot water heat, the non-pressurized system is simply plumbed into the heating lines or connected via a heat exchange unit. An optional electric element on the GARN furnace lets you take advantage of off-peak electric rates as a back-up system.

The entire burning unit is electronically controlled. Combustion air is fed into the chamber by a powerful fan which causes extremely high temperatures of 1,800 degrees to 2,000 degrees inside the chamber. That compares to about 600 degrees in a conventional wood burners. The first moves from the primary 24 by 36-in. chamber to a secondary chamber that is also fed outside fresh air to increase burn. From the secondary chamber, exhaust air is channeled through a long series of ducts that run through the stored water, extracting heat from the exhaust air before it's expelled from the unit. Except for initial startup, there is no smoke from the burner and little creosote is formed, according to the company. Exhaust air comes out the end of the unit. If required there's an access hole on top.

The new furnace is so well insulated that even with a full load of heated-up water, the outside jacket doesn't get hot to the touch. The underground heating pipes are encased in a PVC pipe filled with foam insulation so virtually no heat is lost in transit.

At this time the system is available through Lennox and other selected heating contractors in Minnesota and Wisconsin. GARN plans to make the system available throughout the U.S.and Canada by the fall of 1986.