Glossary of terms: heating, water and plumbing

A

Air vent (bleed valve)

Air in a heating system reveals itself by gurgling, a cold top of the radiator and weaker pump performance. On a radiator you release it with a key through the manual valve. An automatic float air vent is fitted at the highest points of the pipework, on the boiler or on the manifold, where it removes air without any intervention. After bleeding, check the pressure on the pressure gauge and top up with water if necessary. Show products: air vent valves →

B

Backup power supply (UPS) for the boiler and pump

A device with a battery that keeps powering the boiler and the circulation pump when the electricity fails. It is particularly worthwhile with wood or coal boilers, because the fuel keeps burning without power; if the pump stands still, the heat has nowhere to go and the water in the boiler overheats. The boiler electronics and the pump motors need a clean sine-wave voltage, and how long the backup lasts depends on the battery capacity and the load. Show products: Backup Power Supplies - Boilers, Pumps →

Boiler return protection

A measure by which a solid fuel boiler does not receive water that is too cold from the return. Below a certain temperature, flue gases condense on the walls of the heat exchanger, which produces tar and acidic corrosion; manufacturers usually specify a minimum of 60–65 °C. It is ensured by a thermostatic mixing valve in the boiler circuit together with a pump, or by a ready-made charging unit. Show products: boiler and apartment metering units →

Buffer tank

An insulated steel tank filled with heating water stores heat and releases it as the house needs it. A wood boiler can burn fully and cleanly even when the house is not drawing that much heat at that moment; the volume is estimated at 50 to 100 litres for each kW of boiler output. The water in the tank stratifies by temperature, and types with heat exchangers also allow solar heating to be connected. Show products: Buffer Tanks →

C

Circulation pump

It keeps the water moving in a closed heating circuit: it carries it from the heat source to the radiators and back. It does not have to lift it to the height of the house, because it only overcomes the resistance of the pipes, fittings and radiators. Modern models with electronics adapt their speed to the current demand, and therefore use considerably less electricity than older pumps with fixed speeds. Show products: Pumps for Heating and Water →

Compression (screw) fitting

A joint that can be taken apart again. The pipe is pushed onto a nipple with O-rings, and a nut tightens it over a split ring. The demand on tools is small, but the pipe must be cut square and its end calibrated, so that the seals are not torn when it is pushed on. Good practice is to leave such a joint freely accessible, so that it can be checked and tightened later. Show products: Screw Fittings →

Condensing boiler

A gas boiler that also uses the heat from the water vapour in the flue gases: when the flue gases cool below the dew point (approximately 55 °C), the vapour condenses and gives its heat to the water. It works best with a low return temperature, i.e. with underfloor heating or large radiators. The condensate is mildly acidic and is led to the drain, and the flue gases are carried by a flue designed for wet flue gases. Show products: Condensing boilers →

Cooling loop

Safety equipment of a solid fuel boiler that protects it against overheating: when the water reaches about 95 °C, a thermostatic valve lets cold mains water through the heat exchanger of the boiler and the water runs to the drain. The residual heat is thus removed even in a power cut, when the pump stands still. The water supply must not depend on electricity, so a home water pump is not enough.

D

DHW – domestic hot water

Heated drinking water for washing, showering and cooking – different from the water in the closed heating circuit. It is prepared by an indirectly heated cylinder, an electric or instantaneous heater, or a combi boiler. Because of legionella, it is recommended to heat the cylinder regularly to at least 60 °C, with a mixing valve limiting the temperature at the outlets. Show products: Boilers, Water Heaters and Buffer Tanks →

Dirt separator with magnet

A device on the return before the boiler: the water slows down in it, dirt sinks to the bottom and a strong magnet captures magnetite, the fine black sludge from corroding steel. This protects the pump, the heat exchanger and the valves against clogging. It can be cleaned through a drain valve without dismantling, which you will appreciate when replacing the heat source in an old system. Show products: filters and dirt separators →

DN and inch thread sizes

DN is the nominal inside diameter of a pipe or fitting in mm. Inch sizes of threads are only a historical designation and have nothing to do with the real dimension: a thread marked 1/2" has an outside diameter of about 21 mm and corresponds to DN 15, 3/4" belongs to DN 20 and 1" to DN 25. Also tell the types of thread apart: the parallel G thread seals on its face (flat washer, O-ring), the tapered R thread seals directly on the thread, with hemp or PTFE tape. Show products: Brass Threaded Fittings →

E

Electric underfloor heating

Heating without water: the heat is produced by an electric resistance cable, a thin mat in tile adhesive under tiles or in screed, or a foil under a floating floor. The output of mats is around 100–200 W/m², and they are controlled by a thermostat with a floor sensor. The connection is a job for an electrician, and the circuit must be protected by an RCD. Show products: Electric underfloor heating →

Expansion vessel

A vessel with a flexible diaphragm that separates the water from the gas and takes up the extra volume that the water gains when heated (heating from 10 °C to 90 °C is about 3.5 %). This keeps the pressure in the system within a safe range. The gas pre-charge pressure is checked once a year on a vessel without water and is chosen according to the height of the system. For drinking water there are vessels with a suitable diaphragm. Show products: expansion vessels →

F

Flow and return

In a heating circuit the flow carries heated water from the heat source to the radiators, and the return brings it back after it has cooled. At a manifold, valve or pump group, watch the direction of flow (arrows), otherwise the system behaves badly or hums. The efficiency of the heat source depends on the return temperature – a condensing boiler prefers a low one, whereas a solid fuel boiler requires a high one.

Flow meter

On the flow bar of the manifold it shows how much water passes through one circuit (usually in l/min); a float moves in a transparent tube. In most cases it is also a valve: by turning it you set the flow. This makes it possible to balance underfloor heating circuits of different lengths, so that all the rooms heat up equally. Show products: Stainless Steel Manifolds →

G

Gasification wood boiler

A boiler with two chambers. In the upper one, wood with a restricted air supply breaks down into wood gas (gasifies); the gas flows through a nozzle into the lower ceramic chamber, where it burns with secondary air. Combustion is efficient and clean, but it requires wood dried to a moisture content of at most 20 %. It is connected together with a buffer tank and return protection. Show products: Classic and gasification boilers →

H

Heat loss of a building

The heat output that a house loses through its envelope (walls, windows, roof, floor) and through ventilation at the design outdoor temperature. It is calculated according to EN 12831 for the given location; the result determines the heat source and the size of the radiators. If the output of an old boiler is simply copied, the new one tends to be oversized. Show products →

Heating rod (electric heating element)

An electric heater that is screwed into a ladder-type radiator or a tank and heats the water in it; types with a thermostat hold the chosen temperature. Radiators usually have a 1/2" thread, buffer tanks and cylinders a thicker one, for example 6/4". With this kind of operation, never close both valves of the radiator at once, because the heated water would have nowhere to expand. Show products: heating rods, spirals →

Hot water circulation

A loop for distributing hot water: a small pump constantly moves it between the cylinder and the taps, so you do not have to wait for the hot water to arrive when you open the tap. The water circulating in it is drinking water containing oxygen, so a pump made of bronze, brass or stainless steel is suitable; cast iron would rust. To avoid wasting energy, the pump is switched by a timer or a thermostat. Show products: Pumps for Heating and Water →

HT and KG waste pipes

HT pipes are made of polypropylene and serve as internal drainage (washbasins, showers, washing machines); they also withstand hot waste water. They are pushed into a socket with a rubber sealing ring, and horizontal runs are laid with an even fall, usually 1–3 %. For use underground, stronger KG pipes made of PVC in an orange-brown colour are the right choice. Show products: HT Waste System →

Hydraulic balancing

The aim is that the calculated amount of water flows through every radiator, underfloor loop or riser; valves with presetting, balancing valves or flow meters are used. An unbalanced system sends the water along the shortest path – nearby radiators are hot, distant ones merely lukewarm. After balancing, the heat flows evenly, operation is quieter and it spares the pump and the heat source. Show products: riser balancing valves →

Hydraulic separator (low-loss header)

A vertical pipe or vessel of larger diameter that hydraulically disconnects the boiler circuit from the heating branches, so that the pumps on both sides do not interfere with each other. It is suitable for a cascade of boilers, for several pump circuits, or when a boiler requires a minimum flow. The water moves slowly in it, which helps to separate air and sludge. Show products: hydraulic separators →

I

Inspection chamber

An entry to the sewer connection for inspection and cleaning. It is fitted where the direction or the gradient changes, at junctions of branches and at the boundary of the plot. The plastic version consists of a base with connections, a shaft pipe and a cover. The cover is chosen by load: class A15 is enough for gardens and pedestrian areas, B125 for pavements and driveways for passenger cars, and D400 is intended for roads. Show products: Inspection Shafts →

Instantaneous hot water heating

The boiler heats drinking water only at the moment of use, so no cylinder is needed. It is an economical solution for one bathroom; if water is drawn at several places at once or for a large bath, however, the output may not be enough. For instantaneous heating, the heat source selection guide assumes a boiler of at least 24 kW. Show products: Condensing boilers →

M

Manifold (distributor and collector)

A collecting fitting for several circuits. The manifold splits a single supply into several branches (underfloor loops, radiators), and the collector brings the water from them together again and returns it to the heat source. On the flow side you will find flow meters, on the return side valves for actuators. The material is stainless steel or brass, and the outlets usually have a 3/4" thread for a Eurocone fitting. Show products: Stainless Steel Manifolds →

Manifold cabinet

A sheet-metal box that houses the manifold, ball valves and sometimes a pump mixing group. A flush-mounted cabinet is recessed into the masonry, a surface-mounted one hangs on the finished wall. Choose the size according to the whole manifold assembly with accessories, and do not forget the space for the actuators and the terminal block. Show products: Manifold Cabinets →

Mixing valve (3-way and 4-way)

It lets a lower temperature into the circuit by diluting hot water from the heat source with cooler water from the return branch; it is used in underfloor heating and in a weather-compensated radiator circuit. It is adjusted manually or by an actuator according to a controller. A 4-way valve can also warm up the water returning to the boiler. A 3-way valve can also be a diverter – it alternately feeds, for example, the heating and the hot water cylinder. Show products: mixing valves and actuators →

N

Nominal pressure (PN)

The abbreviation PN with a number denotes the pressure class: PN 10 withstands a working overpressure of up to 10 bar at 20 °C. The hotter the medium, the lower the pressure a component can take – plastics noticeably faster than metal. For perspective: the pressure in the heating system of a family house is usually 1–2 bar, whereas the water mains can have 6 bar or more. Show products: ball valves and sanitary fittings →

O

Output modulation

The ability of a burner to change its output smoothly within a range, for example 3 to 24 kW, instead of switching fully on and off. The boiler thus runs longer and more quietly, does not overheat the system and uses less gas. The lower the bottom of the range, the better the boiler adapts to a small heat loss of the house. Show products: Condensing boilers →

Oxygen barrier (EVOH)

A very thin layer, usually of EVOH, that prevents oxygen from the air from passing through the wall of a plastic pipe. Oxygen dissolved in water increases the corrosion of steel and cast-iron parts of the system and produces sludge. For heating, therefore, pipes complying with DIN 4726 should be used; with PEX-AL-PEX the aluminium layer blocks the oxygen. Show products: Pipes for Heating and Water →

P

Pellet boiler

A boiler that burns wood pellets by itself: an auger carries them from the hopper to the burner. Electronics take care of ignition, fuel feed and output, so the user only tops up the fuel and removes the ash. Typical pellets have a diameter of 6 mm and A1 quality according to EN ISO 17225-2; damp or crumbling pellets burn worse.

PEX-AL-PEX multilayer pipe

A multilayer pipe: cross-linked polyethylene (PEX) or PE-RT on the inside and outside, with a bonded aluminium layer between them. The aluminium blocks the passage of oxygen, lets the pipe be bent so that it keeps its shape, and limits the thermal expansion, which is much greater in all-plastic pipes. The size 16 × 2 mm means an outside diameter of 16 mm and a wall thickness of 2 mm. Show products: Pipes for Heating and Water →

Press fitting

A permanent connection: the stainless-steel sleeve of the fitting is deformed on the pipe with press pliers or a pressing machine. The jaws must have a profile (TH, U, B…) matching the fitting system, otherwise the joint will not seal. A properly pressed joint may be built into a wall or cast into the floor. With some fittings, a joint that has not been pressed shows itself during the pressure test by visible leakage of water. Show products: PEX/AL/PEX Press Fittings →

Pressure reducing valve

It passes the water from the mains on at a lower but steady pressure, which is set on the valve itself. While the inlet pressure changes, the outlet pressure stays the same, which protects taps and appliances and prevents the safety valve of a water heater from constantly dripping at high pressure. It is installed after the water meter and the filter. In a household it is mostly set to 3–4 bar. Show products: pressure reducing valves and safety groups →

Pump head and flow rate

Two figures by which a pump is selected. The head (delivery head) describes the resistance the pump can overcome; its unit is the metre of water column (1 m ≈ 0.1 bar). The flow rate, in m³/h or l/min, decreases as the head rises. In reality the pump operates at the point where its curve crosses the curve of the system. The marking 25/6 usually means DN 25 and a head of up to about 6 m. Show products: Pumps for Heating and Water →

R

Radiator valve and lockshield

A radiator is connected by two fittings: on the flow side there is a thermostatic valve under the head, on the return side a lockshield valve, which shuts off the radiator and sets its flow. Valves with presetting determine how much water goes through which radiator and are the basis of hydraulic balancing. For radiators with a bottom connection, a straight or corner H-shaped fitting (centre distance 50 mm) is used. Show products: classic radiator valves →

Room thermostat

A device that senses the air temperature in a reference room and switches the boiler, pump or actuators accordingly; types with communication can adjust the boiler output continuously. Versions with a programme and WiFi lower the temperature at night and when you are away. It belongs on an interior wall at a height of about 1.5 m, far from the radiator and direct sunlight. Thermostatic heads in the same room should be fully open. Show products: Room Thermostats and Controls →

S

Safety valve

A safety device that opens by itself when the set pressure is exceeded and releases some water, so that the boiler, cylinder or pipes do not burst. In heating it usually opens at 2.5 or 3 bar, in water heaters at 6 bar. No shut-off valve may be placed between the protected appliance and the safety valve; the outlet is led through a visible funnel (tundish) into the drain. Show products: safety valves →

Solar collector

A surface that captures solar radiation and heats an antifreeze fluid; the pump station carries it to the heat exchanger in a solar cylinder or in a buffer tank. Flat collectors are cheaper, evacuated-tube ones make better use of the winter sun. With a south-facing installation, roughly 1–1.5 m² of area per person is assumed for water heating. Show products: Solar Sets and Collectors →

System board (studded board)

Expanded polystyrene with studs in a regular grid. The underfloor heating pipe is simply pressed into the studs, no clips are needed. The board insulates the subfloor against heat loss, and the surface film protects the joints against screed seeping through. The pipe spacing is a multiple of the grid, usually 5 cm. Show products: Polystyrene, system boards →

T

Temperature spread

A notation such as 55/45 °C gives the water temperature in the flow and in the return; their difference is the spread, here 10 K. The third number, for example in 75/65/20 °C, is the air temperature in the room. With a larger spread, less water is needed for the same output. The catalogue output of a radiator is given for a particular spread; when the water is cooler, the output drops and the figure has to be recalculated. Show products →

Thermostatic head

It is fitted onto the thermostatic valve on a radiator. As the room warms up, the filling expands and closes the valve, so the temperature is maintained without electricity. The numbers on the scale are temperatures according to the manufacturer – setting 3 usually comes out at around 20 °C. The connecting thread must match (often M30 × 1.5); if the radiator is covered, a head with a remote sensor is useful. Show products: manual, thermostatic and electrothermic heads →

Thermostatic mixing valve

A mechanical valve with a temperature sensor that keeps the set temperature of a mix of hot and cold water by itself; it needs no electricity or control unit. In a hot water distribution it provides scald protection if the cylinder is heated to a higher temperature, for example by solar collectors or a wood boiler. In heating it is used to reduce the temperature of underfloor circuits and to protect the boiler return. Show products: Thermostatic mixing valves →

Towel radiator (ladder radiator)

A bathroom radiator made of horizontal tubes joined by two vertical collector pipes: it heats the room and also dries towels. The connection is from below (at the edges, or in the middle with a 50 mm centre distance) or from the side. The manufacturer states the output for 75/65/20 °C; with cooler water it is lower. A heating rod can be added through a T-piece, so that it warms even outside the heating season. Show products: Towel Radiators →

V

Valve actuator

An electric drive of a valve that acts on the command of a thermostat or controller. Thermoelectric actuators for manifolds and radiator valves have two positions and take several minutes to open; they come as NC (normally closed, closed without power) or NO (normally open) versions, powered by 230 V or 24 V. Motorised actuators move mixing and zone valves and are often controlled by a 0–10 V signal. Show products: Actuators and valves →

W

Water filtration and treatment

Treatment of water after it enters the house: a mechanical filter (strainer, cartridge) holds back sand and rust, which damage fittings and appliances. A cartridge with activated carbon removes chlorine and improves taste and smell, an ion-exchange softener reduces hardness and with it the build-up of limescale. The most reliable approach is to choose the set-up according to a water analysis. Show products: Filtration →

Weather compensation (equithermal control)

The temperature of the water going to the heating changes with the weather: higher in frost, lower in mild weather. The relationship is described by the heating curve; its slope and offset are tuned to the properties of the house. An outdoor sensor is needed, best placed on the north side of the building; the control acts on the boiler output or on the actuator of a mixing valve. Show products: Original Controls for Boilers →

Wet underfloor heating

Pipes embedded in the screed turn the whole floor into a large radiant panel, which needs to be heated only to a mildly warm level; the water in the circuit is roughly 30–45 °C. The floor surface in living rooms must not exceed 29 °C. A loop of pipe with a diameter of 16 mm is sized for roughly 100 m, and the circuits are fed from a manifold. Show products: Underfloor heating →