Hydronic heating
Heating that moves warm water through pipes. In floor heating, the pipes sit under the floor and the whole floor gently warms the room. Our hydronic heating guide explains how it works.
Hydronic heating terms explained
Plain-English meanings for the words you will hear when planning hydronic floor heating. Where a term needs more detail, we link to the page that explains it.
Types of floor heating systems
In-slab heating
Pipes are tied to the reinforcing mesh and cast into a new concrete slab. It suits new builds, and the slab is slow to warm up and cool down.
In-screed heating
Pipes are laid on the slab and covered with a sand and cement screed, often 70–110 mm thick. The screed needs drying time before flooring goes down.
Dry-panel system
Pipes clip into grooved panels laid over the floor, with no wet screed. HOYA Ondol panels are a dry-panel system.
Retrofit
Adding floor heating to an existing home, usually over the current floor while you renovate. See retrofit hydronic floor heating.
Electric floor heating
Heating cables or mats under the floor that run directly on electricity. It is a different system from hydronic heating, which heats water.
Parts of the system
Manifold
The unit that sends warm water to each pipe circuit and takes it back. It usually sits in a cupboard or wall cavity. See pipe and manifolds.
PE-RT pipe
Polyethylene of raised temperature resistance: a flexible pipe made for heating water. HOYA Ondol uses 16 mm PE-RT pipe at 169 mm spacing.
Circuit or loop
One continuous run of pipe from the manifold and back. Each of our circuits is about 90–95 m long and heats roughly 15–16 m².
Heat source
The appliance that heats the water, such as an air-to-water heat pump or a boiler. See heat pumps.
Air-to-water heat pump
A heat pump that takes heat from the outside air and moves it into the heating water. Electricity runs the compressor and fans.
Buffer tank
A small tank of heated water between the heat source and the manifold. Some systems use one to help the heat pump run in longer, steadier cycles.
Thermostat and zones
A zone is an area run by its own thermostat, so rooms you use less can be kept cooler.
Floor and build-up terms
Low-profile system
A floor heating system made to add as little height as possible, using thin panels instead of a thick screed. HOYA Ondol panels add 27.7 mm before the floor finish.
Foil underlay
A thin layer laid under the panels. In the HOYA Ondol build-up it is 1.7 mm thick, under a 26 mm panel.
Tile board
A 6 mm board laid over the panels before tiling, so tiles have a firm, flat base.
Edge strip
A foam strip around the edge of a room that leaves space for the floor to move as it warms and cools. It is used where needed.
Floor build-up
All the layers from the existing floor to the finished surface. With 14.2 mm engineered timber on our panels, the finished floor sits 41.9 mm above the old one. See floor heating heights.
Subfloor
The structural floor under the finished floor: a concrete slab, or timber boards or sheets on joists.
Thermal mass
How much heat a floor stores. A thick slab stores a lot, so it is slow to heat and cool. A thin panel floor stores less and responds sooner.
Warm-up time
How long a cold floor takes to reach its working temperature. It depends on the floor build-up, the floor finish and the heat source.
Design temperature
The cold outdoor temperature a heating system is sized for in your area. The heat loss on that day sets the size of the heat source.
Plumbing and controls
Flow and return
Flow is the warm water going out to the floor. Return is the cooler water coming back to the heat source to be reheated.
Balancing
Setting each circuit at the manifold so every room gets its share of warm water. It is part of commissioning.
Pressure test
Filling the pipe and holding it under pressure to prove there are no leaks before the floor finish goes down.
Circulator pump
The pump that moves water through the heating circuits.
Mixing valve
A valve that blends hot water with returning water to hold the flow temperature at a set level. It is used where the heat source runs hotter than the floor needs.
Expansion tank
A small tank that takes up the extra volume as the heating water warms and expands, so system pressure stays steady.
Room thermostat
A wall control that senses the room temperature and turns that zone on or off.
Zoning valve
A valve, often a small actuator on the manifold, that opens or closes a room’s circuits when its thermostat calls for heat. See pipe and manifolds.
Heat pump terms
SCOP
Seasonal coefficient of performance: the average COP over a whole heating season, not at one test point. It is a better guide to running costs than a single COP rating.
R290 refrigerant
Propane used as the refrigerant in some heat pumps. It has a very low global warming potential. Refrigerant work is done by licensed technicians.
Defrost cycle
In cold, damp weather, ice can form on the outdoor coil of a heat pump. The unit briefly reverses or pauses to melt it, then carries on heating. See heat pumps.
Performance and installation terms
Build-up height
The total thickness the heating adds to the floor before the floor finish goes on. Ours is 27.7 mm: 1.7 mm foil plus a 26 mm panel. See floor heating heights.
Flow temperature
The temperature of the water leaving the heat source. Under engineered timber we design around 35–45 °C.
Floor surface temperature
How warm the floor is underfoot. Under engineered timber we keep it at or below 27 °C. See timber flooring over underfloor heating.
COP
Coefficient of performance: the heat a heat pump delivers for each unit of electricity it uses. A COP of 3 means about 3 kWh of heat for 1 kWh of electricity. It changes with outdoor and water temperatures.
Heat loss
How fast a room loses heat through its walls, windows, floor and roof. It sets how much heat the system must supply, and it drives what floor heating costs.
Commissioning
Filling, pressure testing, balancing and first start-up of the system. It is done by a licensed tradesperson before the heating is used normally.
Compliance and your rights
Licensed plumber
Manifold, heat pump and boiler connections must be made by a licensed plumber, and electrical work by a licensed electrician. In some states, laying the heating pipe is also licensed plumbing work. Warranty requires licensed connections.
Australian Consumer Law
The national law that gives you consumer guarantees on goods and services. Our warranty sits alongside these rights and does not limit them.
Talk to us about your project
Send us your plans and tell us about the floor. We’ll explain the options in plain English and design the layout for your home.
Installation and warranty
The panels can be laid by a builder, carpenter or flooring installer, following HOYA Ondol’s installation instructions and the panel and pipe layout designed for your floor, working with your hydronic installer. Manifold, heat pump or boiler connections must be made by a licensed plumber, and electrical work by a licensed electrician. In some states, laying the heating pipe itself is also licensed plumbing work, so check with your installer. Warranty requires licensed connections. This does not limit your rights under the Australian Consumer Law.