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Main automatic gas valve
A device on a furnace or boiler
that starts and stops the flow of
gas to the burners.
Main disconnect
Fuse(s) or breaker(s) that alone or
together stop the entire flow of
electricity to the home. Located in a service box or the main panel.
Main overload protection device
See Main disconnect.
Main panel
A metal box holding overload protection
devices and/or disconnects for the
home's electrical circuits.
Main shut-off valve
A valve that turns off the water
supply to the house.
Mansard roof
A variation on the hip roof with steeply
sloping sides and a top portion either
flat or meeting in a peak or a ridge.
Manual turn-off
A valve that turns off the fuel supply to
a heating unit.
Master shut-off
A device that turns off electricity to
the heating system and its controls.
Also called a safety switch or serviceman's switch.
Mechanical vent
A device installed for venting purposes
in an unvented location. Does not
vent to the outside.
Metal shower pan
A shower pan made of lead or tin
notorious for leaking,
Mid-efficiencies
Gas and oil furnaces and boilers with an
operating efficiency in the 80%
range. Units typically have an induced draft fan and motorized vent
dampers.
Millboard
An insulating material made of asbestos
and gypsum.
Modulating aquastat
A device in a hot water boiler
that senses outdoor temperature and
changes circulating water temperature requirements accordingly.
Monolithic slab-on-grade
Construction where the slab and
the foundation are poured as
one piece.
Mortar
A mixture of a binder (lime, masonry
cement, portland cement), an aggregate
(sand), and water. Used to bond masonry units such as concrete blocks,
stones, and bricks
together.
Mortise and tenon connections
Joining joists to girders
where a mortise (hole) in the
girder accepts the tenon (a projecting end) of the joist.
Motorized duct damper
A damper located in zoned supply
ducts that controls the flow of
warm from a furnace to zones within the house.
Motorized vent damper
A damper located in the smoke
pipe above a furnace or boiler
that opens and closes automatically to prevent heat loss up the chimney.
Multi-pane window
A window with small pieces of
glass set into wood or lead muntins.
Multiple lights
Glazing consisting of two or three layers
of glass or other material.
Commonly called thermal-panes or Thermopanes, a tradename.
Multiple tapping
See Double tapping and
Tapping before the main.
Muntins
A grid of cross pieces of wood or lead
that hold small panes of glass in a multi-
pane window. |