Underfloor Heating General Principals

The principals of under floor heating (also referred to as radiant heating) remain the same whether using electric or water systems. Heated floors act as efficient low-level radiators, radiating heat energy evenly into the room, gently warming the living space through a combination of radiant energy and heat conduction. In a modern, well insulated room, where heat loss factors have been taken into consideration, underfloor heating can act as the primary heat source: in the majority of cases eliminating the need for radiators.

Radiators convect heat into the room, creating rising currents of warm air concentrating at the ceiling level: this type of convection heating is wasteful and inefficient. Underfloor heating operates by radiating heat energy into the room at the floor level, gently and evenly warming the room: this method of heating is cheaper to run than radiator heating by up to 20%.

Modern underfloor heating is unobtrusive, allowing the freedom to position furnishings and units wherever you want, without having to compromise on design considerations that would otherwise be the case with conventional, wall mounted radiators. By eliminating old fashioned, inefficient radiators from the walls, the days of having to arrange furniture in the warmest spots in the room, close to radiators, are over.

Finally, with radiator heating, no matter how warm the ambient temperature in the room, the floor will always be uncomfortably cold, particularly where hard floor surfaces like tiles or laminate flooring has been chosen. The great advantage of underfloor heating is that this form of heating not only warms the room more efficiently at a lower cost, it also gives a luxurious Mediterranean feel to walk on; tiles and laminate floors now have a welcoming warm surface.

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

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.

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, Heatmiser electronic controls have been developed to manage the system on/off times and control individual room temperatures.

A single 8 zone wiring centre is the hub of the system and can control up to 8 x 230V room thermostats. A touch screen, 4 zone Master Time Clock can be sited in a convenient position and programmed to give complete control for up to 4 grouped zones (like all bedrooms or series of downstairs rooms for instance).

Flush mounted, manual dial, temperature Set Back thermostats are strategically placed in each zone to monitor the room temperatures, allowing the user to micro-manage the underfloor heating down to individual room levels. The thermostat set-back function automatically reduces the temperature by 4°C when it's timed to be off, maintaining the background heat store in the screed sub-floor at an optimum temperature. 

For more information on complete system electronic controls please click on water underfloor heating electronic controls 

For more general answers on wet underfloor heating systems please click on the water under floor 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: