Underfloor heating in Batumi apartments: electric and water

Underfloor heating in an apartment: electric or water

In Batumi apartments we mostly install electric underfloor heating: all it needs is a circuit from the consumer unit, and it can go under almost any floor covering. Water underfloor heating is heated by a boiler, and in an apartment building it is possible when the apartment has its own gas boiler with a heating circuit. Without gas it makes no sense: the water would have to be heated with the same electricity.

Thickness matters too: a water circuit with insulation and screed takes up 7–9 cm and has to go in at the rough-work stage, while a mat in the tile adhesive bed adds only a few millimetres to the floor. Boilers and gas are covered on the page about apartment heating.

Where to lay the heating: zones by furniture

Underfloor heating goes on the open floor area, not across the whole room. Under a wardrobe, kitchen units or a bed on a solid base, the heat is trapped by the furniture and the cable overheats. So before anything is bought we place the furniture on the plan and mark out the zones where people walk and stand.

Heating is most noticeable on tiles: porcelain draws heat away from your feet faster than laminate and feels colder, so the hallway and the kitchen with porcelain floor tiles come first on the list. Heating in the bathroom is covered on the page about bathroom renovation.

Thermostat: sensors, heating limit, control from your phone

Under tiles the thermostat works from a floor sensor and holds the surface temperature. Under laminate and wood we fit a model with two sensors, air and floor, and limit the heating to the figure in the floor covering instructions, so that the joints and the lacquer don't dry out.

A Wi-Fi thermostat lets you switch the floor on from your phone before you arrive. For a rental apartment we set an upper limit on it that a guest can't raise the temperature above. Most thermostats switch up to 16 A, which is about 3.5 kW, and a more powerful zone we connect through a contactor in the consumer unit.

Load on the consumer unit and the apartment's capacity

A mat under tiles usually draws about 150 W per square metre. Heating in the hallway, kitchen and bathroom on about 12 m² of open floor comes to roughly 1.8 kW, and film in two bedrooms adds another 2–3 kW. But on a winter evening the water heater, the hob and the air conditioners are running along with the floor.

So before laying we check the list of appliances against the capacity allocated to the apartment, from the documents or from the main breaker rating. Each zone gets its own circuit with 30 mA RCD protection. If there is no spare capacity, we fit a load priority relay: it temporarily switches off the heating while the water heater or the hob is running. How we assemble a consumer unit with separate heating circuits is described separately, and a capacity increase is arranged through the network company.

How we lay cable, mats and pipes

Heating cable is never cut or shortened: its length sets its power, so we choose the mat or cable reel to fit the size of the zone, and at the wall we cut only the mat's mesh. The cable runs never cross each other and never pass over a movement joint. The connection joint stays in the adhesive or screed, and only the cold tail goes up the wall to the thermostat. We lay the sensor between the cable runs in a conduit with a capped end, so it can be replaced without opening up the floor. We measure the conductor and insulation resistance three times: out of the box, after laying out and after the tiles or screed, and write the figures in the certificate.

We build a water circuit from cross-linked polyethylene (PEX) pipe with an oxygen barrier, and each loop runs from the manifold as one unbroken length. By a floor-to-ceiling window we space the pipe runs closer together, and in the middle of the room further apart. If the same boiler heats radiators, we fit a mixing unit between it and the manifold: the floor needs cooler water than the radiators. Before pouring, we pressure test the circuit and leave it under pressure while the screed to guide rails goes down: if a pipe gets damaged, the gauge shows it straight away.

First start-up of the heating

We run the first start-up to a schedule, and record the dates of pouring and switching on and the temperature for each day in the certificate. Cement screed over pipes or cable gets at least three weeks, and adhesive over a mat the time on its data sheet. For the first three days a water circuit runs on water at about 25 °C, then over several days it is brought up to working temperature, and with electric heating we raise the thermostat just as gradually. This start-up tests the system but doesn't replace drying: before laminate or wood we still measure the moisture of the screed.

How much underfloor heating costs in an apartment in Batumi

Electric underfloor heating with materials costs from 110 to 145 ₾ per m² of heated area, and a water circuit with materials 120–145 ₾ per m². A small zone we price as a single item: laying a mat of up to 5 m² costs 210–240 ₾ in labour, not including the mat. Laying a water circuit as labour only comes to 48–60 ₾ per m².

The thermostat is extra, 240–420 ₾ depending on the model, as is screed if we pour it again, 40–66 ₾ per m², and the floor covering itself. The final cost is set after measuring up and agreeing the estimate.