Water Underfloor Heating

The principals of piped water under floor heating relies on a continuous feed of pumped, circulating warm water – via a mixing valve to an adjusted lower temperature - through the sub-floor substrate; usually a 65-75mm cement screed, but equally can be installed over timber sub-floors.

In the case of a cement screeded sub-floor, this thermal mass becomes a background heat store. To offset the drop in temperature of the cement screed during overnight or off peak times, the thermostat settings can be adjusted to a lower level (setback temperature) to retain the temperature of the screed to within a few degrees below daytime settings - typically 3 - 4°C lower.

If the underfloor heating were to be turned off completely the cement screed would cool down too far below optimum background temperature: depending on time of the year, this would delay room warm up times by up to 2 hours. In order to prevent the screed thermal mass dropping too low, it is more efficient to maintain the floor at a constant lower temperature. Using this setback method will quickly bring the floor heating system back up to normal operating, ambient temperature, thermostat settings.

Water under floor heating has many advantages over traditional radiator heating. When the pipework is incorporated within the screeded sub-floor at the outset, the installation costs are no more than a radiator system; coupled with the added savings on operating costs, the payback time for a water underfloor heating system is financially viable.

Pipework

Floor Heating offer 2 types of water underfloor heating pipe:

Pex Pipe

Qual-PEX barrier pipe incorporates an EVOH barrier layer within the pipe wall. This prevents permeation of oxygen through the tubing. The mixing valves, boilers and other components used in the underfloor heating systems are ferrous (metallic) and are subject to corrosion. To eliminate corrosion due to oxygen permeation, an oxygen barrier pipe should always be used for underfloor heating.

Pex-Al-Pex Pipe

Pex-Al-Pex multilayer pipe is a five-layer composite pipe that combines the advantages of copper and plastic and eliminates their disadvantages.

The aluminium core is absolutely diffusion tight; it reliably prevents oxygen/gases from permeating through the surface. Also, with a 100% diffusion barrier, it helps eliminate corrosion and the build-up of micro-organisms in the pipe and fittings.

When installing the pex-al-pex pipe it provides no memory bend, i.e. it compensates snap-back forces allowing it to be manipulated into the desired shape.

Manifold,  Actuators,  Pump & Blending Valve

The Manifold is the heart of the system, controlling the flow of warm water to each zoned area of pipework.

To provide a fast and simple installtion the pump and blending valve has been combined into a single Manifold Water Temperature Control unit to control the flow of water from the boiler to the underfloor heating pipework to an adjusted and mixed uniform temperature.

Electronic Thermic Actuators are required for the control of water to each zone, allowing the system to operate and control individual rooms. Each actuator is controlled by the room thermostat temperature settings switching the actuator on and off, controlling the flow of water to the zone. 

Electronic Controls

To enable the underfloor heating system to operate efficiently, maintaining the background heat store in the screed sub-floor at an optimum temperature, Heatmiser electronic controls have been developed to manage the system on/off times and maintain control of individual room temperatures.

For full automated control of On/Off times and room temperature settings, each installation will require one or more manifold electronic thermic actuators, thermostats and a wiring centre - depending on individual room control. 

Wired electronic controls 

For efficient and effective control of water underfloor heating installations a wiring centre, central programmable Time Clock and room Set Back thermostats (or individual room, programmable digital thermostats) are recomended to control zone On/Off times and temperature settings.

For more information please click wired electronic controls to view.

To view how to connect a Heatmiser wired system please click on the following pdf: Heatmiser wiring system drawing

Wireless electronic controls

For installations where complete control of the system is required without the need for hard wiring of thermostats, the wireless sytem is the preferred choice.

For more information please click wireless electronic controls to view.

To view how to connect a Heatmiser wireless system please click on the following pdf: Heatmiser wiring system drawing

For more general answers on wet underfloor heating systems please click on the water underfloor heating FAQs page.

Water Underfloor Heating V Electric

The major difference between electric and water systems is in the construction of the floor. Wet systems are especially suited to new floor constructions where the makeup of the sub-floor can accommodate the pipework and cement screed. For existing floors, where overall floor height can be an issue, an electric underfloor heating system would be the preferred option due to the low profile (3mm) of the heating cable: these systems are the ideal choice for refurbishment projects or wooden sub-floors.

Other aspects to consider would be the higher installation cost of a water system compared to a typical electric system; however, gas heating will have a lower overall running cost than electric.

For more information click electric underfloor heating FAQs page.

Floor Finishes and Coverings

Underfloor heating systems are suitable for almost any floor finish; however, it is important to understand the effect of different flooring types. Whichever floor covering is chosen it will become part of heating system, radiating heat energy into the room. Each floor covering will have a greater or lesser degree of efficiency of the underfloor heating, depending on the type of material chosen.

Different floor coverings have different levels of thermal resistance (a measure of the insulation properties of materials): these values are known as the R-value, also referred to as the TOG rating. Manufacturers of continental quilts and carpets use TOG ratings as a measure of the insulation qualities of their products - the higher the TOG values the higher the thermal resistance.

Tiled Floors

In simple terms, harder and denser floor coverings like ceramic or stone tiles all have very low TOG values and as such, less of an insulating effect over the underfloor heating, allowing a rapid transfer of heat energy thorough their structure. The effect of the low TOG rating of these floor types is that their surfaces are excellent emitters of thermal energy (referred to as thermal conductivity or W/mK) - these flooring surfaces will provide the optimum efficiency over an under floor heating system.

Engineered Wood, Timber & Laminate Floors

Engineered wood, timber and laminate floorings have naturally higher TOG values, and depending on thickness, will slow thermal movement through the material: consequently, these materials do not perform as efficiently as tiled floors when radiating heat energy into the room. However, provided the maximum board thickness does not exceed 22mm (or 0.15m²K/W) these floor types will give excellent results when used over underfloor heating.

Vinyl Floors

Vinyl flooring types generally have a low TOG rating and as such offer little thermal resistance to the heat transfer - these floor types will work efficiently with underfloor heating.

Carpet Floors

Carpets and underlays on the other hand are excellent insulators and will generally have higher TOG values: as such these materials will resist the thermal energy being generated by the underfloor heating. If carpets are the preferred choice, select those with low TOG ratings: underlays should also be chosen with low insulation properties.

The thicker the carpet and underlay the longer the warm up time; this will have the effect of slowing the heat transfer of the flooring into the room - these floor types are considered to be the least efficient of all the floor coverings.

If you are unsure whether a certain type of floor covering is suitable for under floor heating, we strongly recommend consulting with the retailer or manufacturer. If in doubt we would advise that specific information should be obtained from the proposed flooring supplier or manufacturer to assess the suitability of the flooring type.

The table below gives some typical flooring resistance values: