Underfloor heating installation glossary of trade terms
18 Irish underfloor heating, manifold, heat pump, screed and Part L building regulation terms defined in plain English.
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Underfloor heating specifications explained A–Z
12mm Low-Profile PE-RT Overlay Pipe
Small-bore 12mm five-layer oxygen-barrier pipe pressed into 15mm–18mm castellated or grooved overlay boards on top of an existing concrete or timber floor when digging out the slab is impractical.
16mm PE-Xa / PE-RT Pipework
The standard 16mm × 2.0mm cross-linked polyethylene or raised-temperature polyethylene pipe clipped at 100mm–200mm centres onto foil-faced PIR insulation in Irish new builds and extensions before the screed pour.
230V Thermal Actuator
An electro-thermal wax-element valve head mounted on each return port of the manifold that opens or closes an individual pipe loop within 2 to 3 minutes when a room thermostat calls for heat.
27°C Timber & LVT Floor Probe Limit
The upper floor-surface temperature cap enforced by a remote NTC thermistor probe embedded in the screed beneath engineered oak, laminate or luxury vinyl tile (LVT) so adhesive and timber never overheat.
35°C Design Flow Temperature
The low water temperature circulated through hydronic underfloor heating loops by an air-to-water heat pump at -3°C outdoor design conditions, delivering a seasonal coefficient of performance (SCOP) of 3.8 to 4.3.
5-Layer EVOH Oxygen-Barrier Pipe
Underfloor heating pipe manufactured to DIN 4726 with an ethylene-vinyl alcohol (EVOH) mid-layer that prevents atmospheric oxygen diffusing through the pipe wall and corroding cast-iron pumps or heat-exchanger components.
Anhydrite (Calcium Sulphate) Liquid Screed
A pump-applied self-levelling floor screed poured at 50mm depth over underfloor heating pipes; it wraps 360° around the pipe with zero air voids and conducts heat nearly twice as fast as dry sand-and-cement.
Blending / Thermostatic Mixing Valve Set
A manifold pump-and-mixer assembly with a 3-way thermostatic valve (35°C–50°C) required when a high-temperature condensing gas or oil boiler (65°C–75°C) feeds an underfloor heating manifold alongside upstairs radiators.
Carbide Bomb / Hygrometer Moisture Test (<75% RH)
The mandatory floor-moisture verification test before bonding porcelain tiles, engineered wood or LVT over a heated screed; anhydrite screed must read below 0.5% residual moisture (or <75% RH) with heating turned off.
Castellated (Egg-Crate) Clip Panel
Moulded high-density studded matrix sheets laid over floor insulation or a primed slab so 12mm or 16mm heating pipe walks into place at exact 50mm grid multiples without separate staples.
Commissioning Heat-Up Protocol (EN 1264-4)
The controlled initial firing cycle after the screed cures — starting at 20°C–25°C flow temperature for 3 days, then stepping up by 5°C per day to maximum design temperature and holding for 4 days — to drive out residual moisture without thermal-shock cracking.
Delta-T (5°C–7°C Flow/Return Differential)
The temperature drop between water entering a pipe loop from the top manifold bar and returning to the bottom bar; a well-balanced heat pump floor operates at a tight 5°C Delta-T so the entire room heats evenly.
Edge / Perimeter Expansion Strip (8mm–10mm)
Closed-cell polyethylene foam ribbon fixed around every wall base, door reveal and kitchen island before pouring screed so the heated slab can expand by up to 0.5mm per linear metre without buckling tiles.
Flow Meter / Sight-Glass Balancing Valve (L/min)
A calibrated transparent rotameter on each flow port of the manifold adjusted between 1.0 and 3.5 litres per minute during commissioning so short bathroom loops cannot starve long open-plan kitchen loops.
Part L Floor U-Value (≤ 0.15 W/m²K)
The Irish Building Regulations Technical Guidance Document L requirement for heated ground floors, typically met using 120mm to 150mm of foil-faced PIR insulation board (λ = 0.022 W/mK) beneath the pipe loops.
Safe Electric REC Restricted Works Certificate
Mandatory certification from a Registered Electrical Contractor for wiring 230V electric heating mats in bathrooms/wetrooms (protected by a 30mA RCD and earth screen) and connecting manifold wiring centres.
SEAI Heat Pump & Central Heating Grant (Up to €14,500)
SEAI grant support for pre-2021 homes installing an air-to-water heat pump system, including up to €2,000 (€1,000 in apartments) specifically towards new or upgraded underfloor heating and radiators.
Tog Value / Thermal Resistance (R-Value ≤ 0.15 m²K/W)
The insulation resistance of the finished floor covering above the screed; porcelain tiles sit at ~0.02 m²K/W (0.2 Tog), 14mm engineered oak sits around 0.10–0.13 m²K/W (1.0–1.3 Tog), and any carpet plus underlay must stay below 2.5 Tog total.
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Underfloor heating installation guides & specifications
Detailed Irish engineering & cost guides covering pipe spacing, manifold balancing, 15mm retrofit overlays, 35°C heat pump commissioning and floor coverings.
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