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GARDEN MACAZINE 

 READERS' SERVICE 



Help in need! Ask this department to answer your specific 

 problem. Replies of general interest only are printed here 



October, 1915 



3 



Size and Arrangement of Pipe 



Kindly tell me what size water pipes to use, 

 and how to arrange them with a small gas water heater, 

 in order to heat under one bench 4 feet wide and about 

 17 feet long, in a small greenhouse 18 feet long, 9 feet 

 wide, 5 foot sides (one having 15 ft. glass) and about 9 

 feet to ridge. Walls are made of concrete. The green- 

 house is connected to cellar. — F. Y., Kentucky. 

 — In a house of this size, either 2-inch or 35-inch pipe 

 may be used, but the larger pipe is more satisfactory. 

 The branches should be left with an open space between 

 them and the wall to allow the heat to rise there. 

 The accompanying plan will make things more plain. 

 The flow pipes are on top and the pipes should be 

 graded to the high point, a couple of inches in such a 

 small house being sufficient. Notice the arrangement 

 of the coils. They rest on piers which can be built 

 of any solid material, such as brick, cement, etc. Cast 

 iron "chairs" are placed on top of the piers which hold 

 the pipes. The return pipes are directly under the flow 

 pipes; the ends have an automatic header which allows 

 the air to escape and prevents the system from be- 

 coming air bound. In place of this header an air cock 

 or pet cock can be placed on the coils at the highest 

 point, and the air can be released by occasionally 

 opening this pet cock. Single valving is shown in the 

 drawing; when a house is divided into more than one 

 compartment it is important to have valves on both 

 the flow and return pipes. In order to decide how to 

 heat the house, we must know the required temperature 

 to be maintained. 



Supposing a temperature of 55 to 60 degrees (night) 

 is wanted, when the outside temperature is zero. 

 Find the amount of exposed glass surface by mul- 

 tiplying the width over the house (15 feet), by the 

 length (18 feet) which gives 270 square feet; add to 

 this the gable, 27 feet, making a total of 297 feet. 

 Add to this 31 feet, the equivalent of glass radiation 

 which is'obtained by dividing by 5 the area of the walls 

 (45 x 32 ft., or 157 feet), and you have a total of 328 

 feet of radiating glass surface. In order to find out 

 how much pipe is needed for a temperature of from 55 

 to 60 degrees, divide by 3, for 35-inch pipe; which 

 results in 109 feet; for 2-inch pipe, multiply 109 by 1.68, 

 which is 183 feet. Therefore, 183 feet of 2-inch pipe is 

 equal to 109 feet of 3-2-inch pipe. 



For a temperature of 45 to 50 degrees, when the 

 outside temperature is zero, proceed as follows; the 

 exposed glass surface is of course, the / 



same 297 sq. ft. Add together 36 feet, 

 the masonry wall on two sides, and 9 

 feet the end, the total being 45 feet; 

 multiply this by the height of wall, 35 

 feet, in order to get the area of the walls, 

 and divide by 5 the resulting 158 square 

 feet =(31 feet) because 5 square feet of 

 wall area is equal to 1 foot of glass area 

 (328 feet), and divide by 4 The result, 

 82, is the number of running feet of 32- 

 inch, pipe required to maintain 45 to 50 

 degrees. And in order to get the amount 

 of 2 -inch pipe needed for this temper- 

 ature, multiply 82 by 1.68. Dividing the 

 sum of the actual glass area and the 

 equivalent glass area of the masonry walls 

 by 3, the result will be a temperature of 

 from 55 to 60 degrees, with zero outside; 

 dividing by 3.46 gives a temperature of 

 50 to 55 degrees, and by 4 45 to 50 degrees all fig- 

 ured for 35-inch piping. When 2-inch pipe is to be 

 installed, multiply by 1.68 the number of feet of 35- 

 inch pipe required. 



It is taken for granted that one end of the greenhouse 

 is attached to another building and is not figured in. 

 If this end was also exposed it would, of course, have to 

 be added to the original 297 feet. It is advisable to 

 allow for a reasonable surplus in boiler power; say 

 25 per cent. For example, figured at a 45 to 50 degree 

 temperature, this house would require 82 feet of 35 



PROBLEMS OF GREENHOUSE HEATING ^^^ £ D $£ a g*g: 6 5± 



still another advises connecting up absolutely 

 tight and putting the entire system under city water 

 pressure. — F. G., 111. 



to this add \ of 90, or 23, making 113. Therefore use 

 a boiler that is rated at more than 113 feet of 35-inch 

 coils. When a very low temperature is specified, all 

 the heat can be put under one bench, but generally 

 that is a bad practice; to get an equal distribution of 

 heat, put piping under both benches. If 2-inch coils 

 are used, they need not necessarily be placed on piers, 

 but can be put on the side wall. Special hangers for 

 the purpose of attaching them may be bought. The 

 mains from the boiler to the coils should always be of 

 sufficient size to insure good circulation. Of course, a 

 house of this size is very easy to heat, and a main of the 



Showing how pipe in house 

 is connected for flow and re- 

 turn 



i ypical section showing 

 heating pipe properly placed 

 under both benches, which 

 are clear from walls 



Plan for efficient distribution of pipe in a small greenhouse 



same size as the heating 

 coils can be used; but in 

 large houses the mains 

 must be figured out prop- 

 erly. When ordering a 

 boiler, always give the 

 total glass and wall area 

 wanted, the distance the 

 boiler is to be placed from 

 the coils and stipulate a 

 25 per cent, or better 

 surplus. For gas heaters, 



apply to Wise Furnace Co., 240 Hamilton Bldg., 

 Akron, Ohio, and the Stewart Gas Heater Co., 

 Pittsburg, Pa. Or you could have installed a standard 

 cast iron boiler, such as is made by greenhouse 

 builders and have it equipped with gas burners at a 

 very small cost. 



Connecting up the Heating System 



I have just completed a greenhouse, 

 18 x 50 ft., of semi-iron construction with 

 pipe posts set 3 feet in the ground and a 

 12-inch concrete wall above that, which 

 is partly filled inside, leaving about 6 or 

 8 inches clear above the grading. Then 

 I have 3 feet of board wall and 2 feet of 

 stationary glass above that. House runs 

 east and west, with west end attached to 

 the work room; the east end has two 3x6 

 doors. Have glazed the entire house. 

 Have bottom opening ventilators on each 

 side of the roof. Under the work room 

 is the boiler pit, 16 x 16 ft. and 8 feet deep 

 in (the clear. I now want to install the 

 heating apparatus and have been advised 

 as follows: Tom has a house with 3 or 

 4 large pipes (4-inch boiler flues) for flows and the 

 same for returns, all under the outside benches, and 

 says it works so well he will install it in another house 

 he is about to build. Dick says by all means use 

 small pipe; say a 2-inch pipe on each plate and per- 

 haps another under the ridge and return under the 

 benches with smaller pipe connected to a manifold. 

 Harry says be sure to have the flow pipe highest at 

 the boiler end, while John says by all means have it 

 the highest at the far end of the house. No two are 

 agreed on any point. One wants the far end of the 



mch coils; add 10 per cent, for mains, making 90 feet; system left open (with a short vertical stub pipe) for 



— Neither Tom, Dick, nor Harry had the right idea in 

 regard to heating the greenhouse. As to size of pipe: 

 that is an old question and has been decided many 

 times in favor of the larger pipe, for the reason that 

 while small pipe has the advantage of heating quickly 

 because of the greater proportion of water exposed, it 

 also has the distinct disadvantage of cooling too quickly, 

 something to be avoided in greenhouse heating. In 

 other words, you want a latent heat, slow in generation 

 but not subject to quick changes. Two-inch pipe is 

 used on large commercial ranges where a night fireman 

 is employed to look after temperature and fires. The 

 average commercial house is so large and contains such 

 a large volume of air that when the proper temperature 

 is reached it is very easy to maintain; but with a small 

 greenhouse of the size mentioned, a 35-inch heating 

 system is preferable. Of course, the 2-inch pipe is 

 much easier to install. 



When a temperature of more than 55 degrees at night 

 is to be maintained it is best to distribute the pipes over 

 the entire house. If all the coils necessary to maintain 

 such a temperature were placed under the side benches 

 only, the heat would cause too rapid evaporation of the 

 moisture in the plant beds; for under 55 degrees night, 

 all the coils can be placed under the side benches. For 

 instance, a standard house, 18 x 50, requires 235 feet 

 of 35-inch coils, or 395 feet of 2-inch pipes in one com- 

 partment, unit end attached to building to maintain 

 a night temperature of 60 degrees at zero weather; 

 the other compartment with gable exposed would 

 require 238 feet of 35-inch pipe or 1.68 times that of 

 2-inch pipe to maintain a temperature of 55 degrees; 

 The warm compartment should have coils under both 

 side and centre benches, and in some cases the coils in 

 the cool compartment are all placed under the side 

 benches because of the partial cooling of the water 

 before striking the cool compartment. It is also 

 essential to have an opening between the benches and 

 the side foundations to allow the heat to rise at this 

 point, which tempers the air at the nearest point of 

 control to the plants. 



As to expansion of water .in the system, the stub 

 pipe referred to is antiquated. An air cock on the end 

 of the coils to release the air, with an expansion tank, is 

 a far better system; but better still, is a system with 

 automatic air release which allows the air to escape 

 automatically and then prevents the system from be- 

 coming air bound. Whatever system is installed, be 

 sure to have an expansion tank which should be placed 

 conveniently in the work room; the higher you get it 

 the better it will be. It should be placed where it is 

 accessible at all times and where it can be easily seen. 

 A glass gauge on the tank tells how the water in the 

 system stands. The tank is also connected to the 

 water supply with a valve, and the system is replenished 

 at this point as required. The top of the tank is fitted 

 with proper overflow so that in case the water expands 

 beyond expectation, the tank simply overflows and no 

 harm is done. The system of rising to the high point 

 just above the boiler and flowing from that point around 

 the greenhouse is only used when cellar depth is not 

 sufficient. It is not recommended for greenhouse heat- 

 ing. No horticultural builder installs such a system 

 except as a last resort in extremely difficult situations. 

 Horizontal heating is the accepted system for green- 

 houses. The pipes are graded all the way from the 

 boiler to end of run. A pitch of one inch in ten feet is 

 sufficient. Do not make tight connection of the green- 

 house system with city pressure; you must have some 

 form of air release to prevent the system getting air 

 bound. The stub pipe referred to is one form, but could 

 not be used with the city pressure as it would overflow. 

 The air cock or automatic header can be used. But 

 when the water in the system expands it will back up 

 the supply, which means lost energy. 



