If the cost of brass piping proves to be excessive, a good quality of iron pipe may be substituted where there is danger of corrosion of lead or of its bursting by great pressure. Iron pipe may be obtained with a lining of block tin, which forms a pure and very satisfactory channel, or a galvanized or zinc coating may be used which will be less expensive. The same methods of piping will be necessary in running iron pipe that we have mentioned in piping with brass, and besides, we must take precaution against condensation which will take place upon iron pipes in warm weather, from the fact that iron conducts heat so rapidly. This condensation will be so great that it may on occasion trickle down and cause damage to paper or decorations. Where there is this danger, the pipes should be run in tubes of zinc which will conduct the water to a safe outlet. This precaution should be taken, even in the case of lead or brass piping, when costly decorations or papers are liable to injury from bursting or leaking pipes.

The fastening and joining of all pipes should be carefully watched to see that they are run in straight lines, with free angles, and that hot water pipes are separated by a little space from cold water pipes so that there will be no transmission of heat from one to the other. All pipes must be run so that they will pitch toward some faucet or waste cock, which must be provided in convenient places and in sufficient numbers to shut off and drain both hot and cold water pipes in any given part of the house, as well as the whole system. In New England it is customary to supply the bath boiler from a separate tank in the attic, this tank being supplied from the regular house service with a ball cock to regulate the supply. The supply from the boiler to the various fixtures is made to return again to the boiler for circulation, which allows hot water to be drawn at once at each fixture. From the highest point of the circulation a small "expansion pipe" is run to the tank and turned over the edge to dicsharge just above the water line, in order to allow the steam and froth from the boiling of the water to escape into the tank. This tank should be supplied with an overflow to some convenient fixture. Outside of New England the tank is generally omitted and the boiler supplied from the house system, but this requires a strong boiler, usually of galvanized iron and is not so satisfactory as the expansion system.