Radiant Dictionary

  • Air Eliminator
    A device for removing small amounts of air from a closed radiant system. An important component of the Expansion and Purge Kit.
  • Anti-freeze
    For the purposes of radiant heat, either Propylene Glycol (non-toxic) or Ethylene Glycol (automotive/toxic). Most commonly used with heat exchangers for freeze protection or snow melt applications.
  • Bleeding the System
    Removing air from a closed radiant system using the Expansion and Purge Kit. For more information see Filling the Closed System in the Installation Details section of this site.
  • Brass Adaptors
    Brass fittings used to convert from 3/4″ rigid copper pipe to plastic Polyethylene tubing.
  • Brass Couplings
    Brass fittings used to join two pieces of plastic heat exchanger tubing.
  • BTU
    British thermal unit. A way of measuring heat energy. Or if you want to get technical: the quantity of heat required to raise the temperature of 1 pound of water by 1 degree F.
  • Circuit
    A length of tubing within a zone. Also called a “loop”. Often, many circuits of the same length constitute a zone.
  • Circulator Pump
    A small, low wattage water pump used to circulate heated fluid through tubing in a radiant system.
  • Closed System
    A radiant heating system that uses a dedicated heat source to warm a space. A closed system re-circulates the same fluid around and around in a continuous circuit, completely separate from the domestic water supply.
  • Dry Mix
    A mixture of 4 parts sand and 1 part Portland cement often used as thermal mass in a “suspended slab” installation. For more information see The Suspended Slab in the Installation Details section of this site.
  • Expansion and Purge Kit
    A factory assembled plumbing package containing fill and drain valves, expansion tank, air eliminator, pressure gauge, and pressure relief valve. Its function is to facilitate the removal of air from the newly installed radiant tubing and to maintain a balanced and efficient heating system.
  • Expansion Tank
    A tank containing a pre-pressurized rubber membrane. It is used in closed radiant systems to absorb the expansion of water that results when liquid is heated from cold to hot.
  • Glycol
    Anti-freeze, either Propylene (non-toxic/domestic use) or ethylene (toxic/automotive use) glycol.
  • Gypcrete
    A lightweight concrete product often used when pouring a thin slab over an existing floor.
  • Header
    A copper supply line or return line used mainly in radiant staple-up systems. Basically an elongated site-built manifold, headers are useful because they allow the installer to tap off of a single, long copper line to feed multiple circuits of tubing within a single zone. Headers bring the heated fluid to the circuits instead of […]
  • Heat Diffusion Plates
    Pure aluminum plates, 16″ long by 8″ wide, used to attach radiant tubing to the underside of the floor to be heated. The thermal properties of aluminum guarantee that heat drawn from the tubing will transfer efficiently to the floor.
  • Heat Exchanger
    A device used in some radiant systems to separate dissimilar fluids such as anti-freeze and water. Heat exchangers transfer heat from one fluid to another without allowing direct contact between the fluids.
  • Heat Exchanger System
    A type of radiant heating system that uses a heat exchanger to separate the anti-freeze in the floor from the potable domestic hot water supply. This allows one heat source to provide hot water for both applications.
  • Heat Source
    A water heater or boiler used to provide 120 to 130 degree water to a radiant floor. A heat source can be fed by any fuel, including gas, solar, wood, geothermal, oil, or electric.
  • Loops
    See Circuit.
  • Mixing Valve
    A device used to supply a consistent, lower, pre-regulated water temperature to a radiant system. Mixing valves are most often used in conjunction with high temperature boilers, many designed to heat water to temperatures in excess of 160 degrees. In radiant floor applications, mixing valves do not lower the boiler temperature. Instead, they are plumbed […]
  • Open System
    A radiant system integrated into the home’s plumbing system. In other words, the same water that ends up in your hot shower has passed through the floor first. Open systems use one heat source to heat both the floor and the domestic water. It’s an efficient system because one properly sized water heater doing two […]
  • Poly Tubing
    Slang for Polyethylene tubing. Poly tubing retains many of the heat exchanging properties of copper, but exhibits much greater flexibility and longevity. Poly tubing will last well over 100 years in radiant heat applications.
  • Pressure in System
    “Closed” radiant systems circulate the same fluid around and around in a closed circuit, using the fluid as a heat transfer medium. A “closed” system generally operates at a pressure of around 15-psi. “Open” systems are basically part of the domestic plumbing system. They operate at the same pressure as the house supply, generally around […]
  • Pressure Testing
    A feature built into a slab manifold. It is used to test for leaks prior to pouring a concrete slab and for maintaining a positive pressure in the tubing during the pour.
  • R-value
    A measure of a given material’s ability to resist heat flow. Fiberglass has a very high R-value. That’s why it’s used in walls to slow the transfer of heat to the outside. Wood has a very low R-value. That’s why the walls need the fiberglass.
  • Radial Flooring
  • Radiant Barrier
    Generally a paper thin, pure aluminum material used to reflect 97% of the infrared heat spectrum back up to the heated floor. For more information see The Floor Joist Installation in the Installation Details section of this site.
  • Recovery Rate
    Basically, how fast a water heater or boiler can heat water. Recovery rates are generally measured by how many gallons of water can be raised 90-degrees in one hour. If a water heater, for example, stores 50 gallons of water, a recovery rate suitable for radiant heating would be the ability to heat 1 1/2 […]
  • Recovery Rate
    Basically, how fast a water heater or boiler can heat water. Recovery rates are generally measured by how many gallons of water can be raised 90-degrees in one hour. If a water heater, for example, stores 50 gallons of water, a recovery rate suitable for radiant heating would be the ability to heat 1 1/2 […]
  • Repair Coupling
    A brass fitting used to repair a damaged section of radiant tubing, generally in a slab application. The coupling is sheathed with rubber tape to prevent the concrete from corroding the metal fitting.
  • Repair Coupling
    A brass fitting used to repair a damaged section of radiant tubing, generally in a slab application. The coupling is sheathed with rubber tape to prevent the concrete from corroding the metal fitting.
  • Resistance
    In radiant heating applications, resistance refers to pressure within multiple circuits of tubing. In practice, this simply means that all circuits should be the same length, within about 20-ft. No single circuit should be shorter than the others and thereby offer the water a path of least resistance to follow. With even circuits, water flows […]
  • Return Line
    An insulated copper line leading back to the heat source.
  • Slab Manifold
    A copper manifold used to distribute heated fluid to a concrete slab. Slab manifolds come in many configurations, the simplest being the “1-loop” manifold. This is simply a supply connection to a single loop of tubing and its return. A “6-loop” manifold is generally the largest. Bigger than “6-loop”, and the manifold becomes unwieldy. Imagine […]
  • Sleepers
    Strapping placed on an existing floor to create “sleeper bays” in which to run radiant tubing. Most often, 2 by 4’s laying flat, 16″ on center, act as the best sleepers. They raise the floor 1 1/2″ and allow adequate room for even the largest tubing. Sand or concrete is generally placed over the tubing, […]
  • Staple-up System
    Tubing stapled to the underside of the sub-floor. For more information see The Floor Joist Installation in the Installation Details section of this site.
  • Supply Line
    Generally, an insulated copper line used to feed multiple circuits of tubing. Or, any water line running from the discharge side of a radiant circulator pump.
  • Suspended Slab
    A radiant floor system installed on top of an existing floor. For more information see The Suspended Slab Installation in the Installation Details section of this site.
  • Thermal Mass
    In the context of radiant heat, materials capable of absorbing and storing heat energy. Concrete, sand, slate, and tile possess a greater thermal mass than wood. The greater the mass, the longer stored heat will remain in the floor.
  • Tubing Sizes
    For most practical applications, two tubing sizes are best. 7/8″ Poly and 1/2″ PEX offer the greatest flexibility. The 7/8″ Poly provides the highest heat output (50 BTU’s per ft.) and can be spaced 16″ on center. But a compromise is made when it comes to bending diameter. However, in a wide open slab environment, […]
  • XPS Foam
    Short for Extruded Polystyrene. A rigid insulation often called Pink board or Blue board and used to insulate around the edges of, and below, radiantly heated slabs. It is used primarily for its high R-value and resistance to water saturation.
  • Zone
    Any heated area regulated by one thermostat and supplied by one circulator pump. One zone may contain many parallel circuits of tubing, literally thousands of feet of tubing, and encompass an entire living space, but the whole area will maintain the same, even temperature.
  • Zone Manifold
    Most often a factory built manifold that contains the circulator pumps, ball valves, check valves, in line thermometers, pump flanges, drain valves, and all the plumbing hardware necessary to effectively distribute heated fluid to multiple heating zones.