49. Heating and ventilating work should be estimated as indicated in the following paragraphs.

Estimate all pipes and fittings same as for plumbing. Sum up all standard radiators, and the price by square foot of radiation. Figure special radiators separately.

Itemize all valves, air vents, hangers, etc.

Estimate on pipe coverings by lineal foot.

Estimate sheet-metal indirect-radiator casings in pounds.

Estimate sheet-metal flues and smoke pipes by the lineal foot; but elbows and dampers separately.

Estimate register boxes, registers, and borders separately.

Make separate items of expansion tanks, hot-water damper regulators, and furnace regulators.

Figure heaters, steam boilers, and furnaces from manufacturer's catalogues.

In estimating on heating by furnace, the average cost of labor is about one-third that of materials. In steam and hot-water heating, the ratio is about one-fifth.

The cost of a hot-air installation is approximately 5 per cent. of the cost of the building; for steam heating, 8 per cent.; and for hot-water heating, 10 per cent.