112 



VEGETABLE GARDENING 



i6i. Heating frames by the use of flues. — ]\Iany gi-ow- 

 crs heat their frames I13' a sj'stem of flues leading from a 

 furnace burning wood or coal. The plan is regarded as 

 more economical than the hotl)ed method, and the results, 

 ^\■ith proper management, are equally satisfactory. The 

 furnace or fire box at one end of the frame is cheaply 

 constructed, and should be 3 or 4 feet long, and about 18 

 inches square, with provision for an ash pit under the 

 grate bars. A main flue is built from the fire box, ex- 

 tending 8 or 10 feet under the soil of the frame, where it 



FIG. 21. STEAM-IIEATED FRAME 



separates into two smaller flues that continue almost to 

 the other end of the frame, wdiich may be at least 60 feet 

 long, before they join again and enter a chimney. Figure 

 20 shows this system of heating, but in a difl:erent form 

 of construction. The flues may be made of l^rick, stone 

 or tile, and may vary from 6 to 12 inches in size. Ten- 

 inch tile are very satisfactory. Near the furnace the flue 

 sliould be about 3 feet under the surface, rising gradually 

 to I foot at the chimney. The air in the flue-heated 



