Building Material Concerns:
Selection of wood flooring species, milling (quarter sawn or plane sawn) acclimation period, regulation of relative humidity for dimensional stability and surface temperatures for comfort.
R values of floor assemblies
Control/expansion joints and crack suppression in concrete and tiled surfaces.
Emissivity of surfaces.
Curing times and temperatures for poured floors (concrete, lightweight toppings).
Control System (see Hydronic heating systems):
Fluid temperature in heating and cooling plant.
Fluid temperature in distribution network.
Fluid temperature in the pex piping systems. A function of the spacing, load (Btuh/sf), upward and downward losses and floor r value.
Operative temperature (average of mrt and dry bulb).
Surface temperatures for comfort, safety, and material integrity.
Cost of hot water systems
Although it can be more expensive to install than radiators (it can be comparable due to the increasingly competitive market), wet underfloor heating often proves more economical in the long run, particularly in well-insulated larger properties. Energy savings of up to 40% can be achieved compared to conventional heating systems if a condensing boiler or solar thermal system is installed, but even with a standard boiler up to 15% energy savings are normal [3]. The efficiency of condensing boilers is enhanced thanks to water returning at a lower temperature.
By employing full lengths of piping without any joints, wet underfloor heating loops are practically maintenance free. The piping used can have a lifespan of up to 100 years. Reliable materials are critical because repair is difficult. The central heating equipment, pumps, and controls, like others, requires periodic maintenance and replacement.
Electric floor heating systems
Electric floor heating systems have very low installation cost for smaller spaces (1-5 rooms) because they are easy to install and have a very low start-up cost (a thermostat is all that is required and costs only about $100-$200). Although electric floor heating systems work well as a primary heat source, most systems are installed in the bathroom to add comfort and warmth to cold tile.
Electric floor heating systems are also typically installed in kitchens, bathrooms or in rooms that require additional heat (such as a cold basement, an addition or a kids' playroom, low voltage electric systems are suitable for entire home installations. Rooms can be zoned with their own thermostat and programmed around the schedule of the inhabitant, this can add efficiency to an entire homes energy consumption.
Another advantage of electric underfloor heating over a warm-water system is the floor build up/height. Floor build up can be as little as 1 mm. The electric cables are usually installed onto an insulation board or directly onto the subfloor or padding (under carpet or laminate); then the floor covering is placed directly over the heating system or thinset.
Electric underfloor heating also benefits from faster installation times, with a typical installation only taking half day to a day depending on size to install. Also warm up times are generally a lot quicker than "wet" systems because the cables are installed directly below the finished flooring making it a direct acting heat source rather than a storage heater.
Electric system are supplied in several different forms. They can be one long continuous length of cable with the consumer having to weave the cable up and down the floor at a pre-determined spacing and making a return loop to complete the circuit, or they can be provided in mat form, where the heating element is pre-formed in a mat that rolls out onto the floor. Most high voltage cables have a built in return, meaning that you have one end to connect. Most low voltage technologies consist of a loop with a start and end. With the introduction of the built in return came the “cable mat”. Cable mats have added to the ease of installing a floor heating system by having the heating cable already pre-spaced on to a nylon mesh. Cable mats however can cause issues for odd shaped spaces where a free rolled cable may be able to cover in a more custom pattern. Also to take into account is longevity of a system considering high voltage and low voltage technologies.
One technique is to lay the heating cable directly onto an insulated concrete floor and then apply tile on top of it. Where time-of-use electricity metering is available, this type of system can be turned on at night when electricity rates are low, and then allowed to warm the house during the day by relying on the heat energy held within the thermal mass of the concrete.
Sometimes, in order to minimize floor buildup, a low voltage bronze screen or a carbon film heating element is used. Carbon film systems are normally installed onto a thin insulation underlay (approx 6mm) to reduce thermal loss to the sub-floor. Carbon film is used under various floor finishes, traditionally laminate flooring or engineered wood. Vinyls, carpets and other "soft" floor finishes can be heated using carbon film elements or low voltage bronze screen elements, provided a suitable overboarding system is used.
In comparison to combustion/hydronic systems, electric systems can be more efficient, if only the efficiency of the equipment in the building is considered. However, as discussed in the article on electric heating, the efficiency of generating electricity from fossil fuels is low. Electric systems however are either on or off and do not require idling times. Electric systems also have the advantage of needing no maintenance and can more easily be controlled to run when and where they are needed. However, electric underfloor heating systems cannot provide cooling in summer.
