H Definitions

Definition Categories

Head lap

Head lap is the distance one piece of material covers another piece of material. The term is used in roof coverings to describe how far an upper layer of material covers a lower piece of material. See Exposure.


The hearth is the floor of the firebox

Hearth extension

The hearth extension is the area in front of the firebox, made of noncombustible Material, upon which sparks and hot materials from the firebox may land without starting a fire.


Hub (hubless)

A hub is an enlarged opening molded on the end of a pipe or a fitting into which a section of pipe (the spigot) is inserted. In older plumbing, cast iron hubs and spigots were sealed with oakum or hemp and lead. In modern plumbing, you may seal cast iron hubs and spigots with an elastomeric O-ring gasket or you may remove the hub and convert the pipe into a hubless pipe. A hubless pipe is one without a hub. Hubless pipe joints are often sealed by an elastomeric sleeve held in place by stainless steel rings.


HVAC is an acronym for heating, ventilation, and air conditioning.