There are many excellent insulating materials, made in block form and in various shapes, to be used on boilers. Magnesia makes an excellent block for boiler insulation. These blocks are cemented to the boiler and covered with an asbestos cement. While this type of insulation is same: what more expensive than others, it is also more efficient.
One kind of boiler insulation which the home mechanic can apply with relative ease, and at a reasonably low cost, is asbestos cement. Asbestos cement is not the best kind of insulation, but will provide a good measure of protection.
Asbestos cement is obtainable in 100 pound bags and in smaller quantities. You can figure that 100 pounds will cover from 20 to 25 square feet of surface, at a thickness of one inch. Mix the cement with water until it becomes a workable paste. The only other requirement is some one-inch mesh wire, commonly known as chicken wire, which is used as a reinforcement for the cement.
Before applying the insulation, remove any dirt or rust scales from the outside of the boiler. Check all gauges and pipe connections at the boiler for signs of leaks. The boiler should be warm when the cement is applied ; a cold boiler will expand, when heated, and crack the cement.
Mix the asbestos cement with the water and apply it to the boiler with a trowel. The first coat should be about one inch thick and should be worked into all joints and cracks so that the surface is even. Allow enough room around the ash pit and fire doors, and other openings, so that they may be opened without chipping the edges of the insulation. Scratch this first coat until it presents a rough surface to which the second coat can cling.
Allow enough time for the first coat to become moderately dry, then carefully stretch the chicken wire over the boiler surface. Flatten the wire along the entire surface and. cut the necessary holes in the wire for gauges and other fittings. Cover as much of the surface as possible with the wire and do not be concerned if some of the first coat cracks during this process. After the wire has been secured, apply the second coat of asbestos cement.
The second and final coat should be about
one-half inch thick, and the surface smoothed off with a trowel.
The insulation is composed of corrugated asbestos paper I covered with a canvas jacket. It is in tubular form, and is split lengthwise on one side so that it can be slipped over the pipe. After the insulation is on, a flap of the canvas jacket is pasted over the joint to seal it. For additional support, metal bands are provided to put around the insulation at regular intervals.
Air cell insulation can be had in several thicknesses, the thickest having the best insulating qualities. The sections are about three feet long, and the insulation is ordered according to the size of pipe to be covered. To estimate the amount needed, measure the length of all pipes to be covered-minus fittings and valves, which cannot be covered with this material. Apply later a coat of asbestos cement to fittings and valves.
Inspect the pipes, before covering them, for leaks. Clean the pipes thoroughly. Open a section of the insulation and apply paste to the flap. This paste is usually provided with the insulation, but it can be made by mixing one part powdered alum with 50 parts sifted white flour. Add sufficient cold water to make a smooth paste. Pour in boiling water until the paste is thick.
Slip a section of insulation over the pipe, with the opening up, and press the canvas flap down tightly so that the joint is sealed. One end of each section of insulation has a canvas overlap in order that a tight seal can be made between two sections of insulation.
Push the two sections together so that they fit tightly against each other and paste the canvas overlap around the joint. Cover the entire length of pipe, with the exception of fittings and valves. When short lengths of insulation are needed, they can be cut with a knife.
The metal bands should be put around the sections of insulation at eighteen-inch intervals, and should be spaced to cover the joints between sections as well as provide support in the middle of each section. The bands can be fastened tightly by using a pair of pliers.
After the tubular insulation is on, cover the fittings and valves with asbestos cement. Put on two coats of cement, the first coat one-half inch thick and the second coat applied until this insulation is as thick as that on the pipes.
Leave the valves free of insulation. The return line on a two-pipe heating system is usually not insulated, because if the steam fails to condense the moisture in the radiator, leaving the line uninsulated will let the steam condense before it reaches the boiler.
The hot water storage tank can be covered with insulation in much the same manner as the boiler. More efficient is ready-made insulation which comes in sections and is attached to the tank by means of metal bands or other devices. Holes can be cut in this insulation for the pipes. Cover the top and bottom of tank with asbestos cement. Ready-made insulation is made for both vertical and horizontal tanks and is ordered to the capacity of the tank.
Make it a practice to check the condition of the insulation on boilers and pipes to see if there are any cracks and breaks. These can be quickly filled with a little asbestos cement.
Warm air furnace
Warm air furnaces and ducts are usually insulated with three layers of corrugated asbestos paper. This paper is purchased in rolls containing about 250 square feet of paper. The paper is held to the pipes and furnace by means of metal bands or wire.
Measure the circumference of the furnace and pipes before cutting the paper, and add several inches to this figure to allow for the thickness of the insulating paper. Cover the sloped sections of the furnace with asbestos cement. The top of the furnace is sometimes covered with sand for additional protection against fire, and this surface can also be covered with two or three thicknesses of asbestos paper.
In most cases the outside of the furnace casing will not require insulation because the air between it and the firepot will act as insulation. The greatest heat loss in a warm air system takes place in the ducts.