Air Eliminator / Air Purging Vent
     Device used to automatically eliminate air trapped in a hydronic system.

Ambient Temperature
     The air temperature in a given location - radiant systems can be designed to work with an ambient air thermostat or with a floor temperature sensor.

Ambient Temperature
     The air temperature in a given location.  Most thermostats work by reading the ambient air temperature.  Radiant systems can be controlled by thermostats and by floor temperature sensors.

Anti-freeze
     Propylene Glycol is non-toxic / Ethylene Glycol is toxic - commonly used in indirect or closed systems for snow melt applications and for freeze protection.

Aquastat
     Senses the water temperature in the pressure vessel of a boiler or the tank of a water heater - the heat source monitors this sensor and maintains the system operating temperature by controlling combustion.

Backerboard
     Sometimes referred to as backer or backing board, cement board or Hardibacker.  Used primarily under tile projects.  Conducive to effective in-floor radiant heating.

Baseboard, Radiant or Hydronic
     Used sometimes to augment heat in an area where in-floor radiant may not be possible.  Common in remodeling projects and in some timberframe home loft areas.

 Boiler
     Heat source for radiant panel and domestic hot water heating systems.  Sometimes the term is interchanged with "hot water heater."   Technically, operating temperatures of radiant systems range from 100F to 180F, so no water is ever really boiled.  Boilers produce heat in their combustion system.  Water is pumped through the pressure vessel, picking up the heat and then transfers that heat to the radiant loops and/or indirect water heater.  See also "water heater".

BTU
     British Thermal Unit - a measurement of heating energy.  In technical terms, a BTU is the amount of heat needed to raise the temperature of 1 pound of water by one degree F starting at 39.2F.  Normally measured over time.  BTUH means BTU's per hour and MBH stands for 1,000 BTUH.

Building Codes
     The requirements set forth by the municipality where construction will take place.  The Uniform Building Code (UBC) is recognized nationally, however individual jurisdictions may vary or include modifications to the UBC.

CADD
     Stands for computer aided design and drafting.  AutoCAD is a software program commonly used for architectural design.  LoopCAD is a program used to superimpose radiant loop layouts over existing floor plans.

Carpet
     Common floor covering made of synthetic or natural woven fibers.  Not as conductive as tile or linoleum, but can be used in a radiant system is it is taken into account by your radiant designer.

Carpet Pad
     Refers to the "cushion" used between the carpet and slab or sub floor.  Most radiant designers will recommend a carpet pad with an r-value of 2 or less.  The lower the r-value for the carpet pad and carpet - the more effective the radiant heating system will be.

Ceramic Tile
     These are flat tiles made from quartz, sand and/or clay.  Often used in bathrooms and kitchens.  Ideal for radiant because of the low r-value.

Chalk Line
     A straight line created by snapping a chalk covered string against a surface.  Chalk lines can be used as guidelines for straight runs of radiant PEX tubing or electric cables.

 Circuit
     Used interchangably with the term "loop."  Refers to a length of tubing within a heating zone.  Larger zones may require multiple circuits.

Closed System
     With regard to radiant heating, a closed system is dedicated to space heating only.  The same heating fluid is re-circulated within a closed system.  A separate water heater would be used for any domestic hot water needs.

Conduction
     Heat is transferred between two solid object that are touching.  Heat flows from warmest to coolest.  Some floor coverings are more conductive (lower r-value) - these work better when used with radiant heating systems.

Convection
     Heat is transferred by air movement.  Forced air heating systems use this principle to move heat around.  It works, but is somewhat inefficient and lacks the comfort of radiant in-floor heating.

Distribution Manifold
     See manifold

EPS Foam
     Stands for Extruded Polystyrene.  EPS is also called Pink or Blue board.  It is used to insulate below and around the edges of concrete slabs, particularly radiant slabs.  It has a high r-value and is resistant to water saturation.

Expansion Tank
     A closed tank containing a pre-pressurized membrane, used in hot water and closed radiant systems to absorb the expansion of liquid as it is heated.  It helps maintain a consistent pressure level in the system.

Fuel Source
     Used by the heat source - most common are natural gas, oil, electricity, propane, wood.  Some alternative fuel sources would include: bio-deisel, geo-thermal, solar, waste-oil, corn...

GPM
     Gallons per minute.

Gypcrete
     A lightweight concrete mix of gypsum aggregates used to pour a thin slab over an existing sub floor or slab.  If properly designed and installed it is well-suited to radiant heat.

Header
     Refers to the line of supply or return ports that make up a manifold.

Heat Diffusion or Transfer Plates
     Typically made of aluminum, these can be used to attach radiant tubing to the underside of your sub-floor.  They spread the heat across the underside of the floor  - an alternative to relective insulation.

Heat Exchanger
      A component used to separate potable from non-potable water while allowing a single heat source to provide hot water for heating and domestic usage.  Part of an Indirect System.

HVAC
     Short for heating, ventilation and air conditioning - refers to the process of regulating temperature and comfort in residential and commercial structures.

Hydronic
     All forms of hot water-based heating systems are referred to as hydronic.