| Term | Definition |
|---|
| Handhole | An access opening in a pressure part usually not exceeding 6" in its longest dimension.
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| Handhole Cover | A handhole closure.
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| Hard Water | Water which contains calcium or magnesium in an amount which require an excessive amount of soap to form a lather.
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| Hardness | A measure of the amount of calcium and magnesium salts in water. Usually expressed as grains per gallon or ppm as CaCO3.
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| Heat Available | The thermal energy above a fixed datum that is capable of being absorbed for useful work.
|
| Heat Balance | An accounting of the distribution of the heat input, output and losses.
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| Heat Exchanger | A vessel in which heat is transferred from one medium to another.
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| Heat Release Rate | Rate that describes the heat available per square foot of heat-absorbing surface in the furnace or per cubic foot of volume.
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| Heating Surface | Those surfaces which are exposed to products of
combustion on one side and water on the other. This surface is measured on the side receiving the heat.
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| Heating Value | The quantity of heat released by a fuel through complete combustion. It is commonly expressed in Btu per lb, per gallon, or cu-ft.
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| High Gas Pressure Control | A control to stop the burner if the gas pressure is too high.
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| High Oil Temperature Control | A control to stop the burner if the oil temperature is too high.
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| Hydrocarbon | A chemical compound of hydrogen and carbon.
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| Hydrostatic Test | A strength and tightness test of a closed pressure vessel by water pressure.
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