To draw off water, open the draw-off cock at the lowest point in the system, and then open air cocks on all radiators as fast as the water lowers beginning with the highest radiator. =Air-vent Valves on Radiators.=--In order to secure the full benefit of the heating surface of a hot-water radiator, the inside of the section must be free of air. When a radiator is “air-bound” it means that parts of the sections are filled with air in pockets which remain until the air is allowed to pass off through the vent valve. Air will gather from time to time at the highest points inside the radiators, especially in those placed in the upper stories of the building. These air accumulations inside cut down the working power of a radiator exactly in proportion as they rob the inside of the casting of proper contact with heated water. Air pockets not only reduce effective heating surface, but they also prevent the circulation of hot water. Therefore, it is well once in a while to take the little key provided by the heating contractor and open the air valves on radiators to allow the air (if any) to escape. When a radiator does not work as well as usual, open the air valves until the water flows, which indicates that the air has been fully released. Then close the valve. =Valves on Cellar Mains.=--If cut-off valves have been placed on the main and return pipes in the cellar, see that the valves on one line of main and return pipes (at least) are open when the boiler is under operation. Be sure that the system is open to circulate water through the supply and return pipes before building a fire in the boiler. =End of the Season.=--At the close of the heating season clean all the fire and flue surfaces of the boiler. Let the water remain in the system during the summer months. No bad results will follow if the system is not refilled more often than once in 2 or 3 years. But, generally, it is thought that best results are secured by emptying the system once a year (after fire is out) and refilling with fresh water. It is a very good idea to take down the smoke pipe in the spring, thoroughly clean and put it back in place. Leave all doors open on the boiler in the summer time. =Other Rules for Steam Boilers=--_To Fill Boiler._--Open the feed-cock when the heater is connected with city or town water supply; if not, fill through the funnel. Let the water run until the gage-glass shows about half full of water. In the first filling, after the water has boiled, get up a pressure of at least 10 pounds, draw the fire and blow off the boiler under pressure through draw-off cock to remove oil and sediment, after which refill with fresh water to the water line. This is best done usually by the steam-fitter.