Under-sink water heater: how to install a boiler under the sink

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A water heater installed under the kitchen sink or bathroom sink helps save space in small apartments and does not violate the aesthetics of the room. Let’s look at the types of boilers that you can install with your own hands, deal with fittings and installation steps in order to avoid common mistakes.

Under-sink water heater: how to install a boiler under the sink

A permanent or backup source of hot water in the kitchen can be a water heater, which is installed under the sink – there is always a place there, and it does not interfere with anything. Which boiler to choose and how to install it correctly?

Types of water heaters for installation under the sink

Since the space under the sink is still limited, you can install there either a storage small-capacity water heater with a volume of 10-25 liters or a flow-through one. Heating in them is carried out by open-type electric heaters or heating elements. Gas boilers are usually of higher capacity and are manufactured only for standard wall mounting..

Under-sink water heater: how to install a boiler under the sink

Heaters for installation under the sink differ in the location of the pipe supply – the upper one. When buying a heater, you must pay attention to this, otherwise the device for mounting above the sink, installed under the sink, will work poorly and for a short time..

So which water heater is better – storage (capacitive) or flow (pressure)

Storage heaters take up more space and are more expensive, but their power consumption is lower than in flow heaters (up to 3 kW), and they can provide a larger volume of hot water per minute.

Under-sink water heater: how to install a boiler under the sink Storage water heater

Since the instantaneous water heater has a relatively high power for household consumption – up to 8 kW, you need to make sure that the electrical network in the apartment or house is able to provide it without constantly knocking out the machines. If the heater is intended only for the duration of the pressure test by the heating network, when in summer hot water is turned off for 2 weeks, then heating of 2 l / min will require no more than 3.6 kW of power. Cold “winter” water cannot be heated in such a volume even up to 30 ° C. For year-round consumption, either a storage water heater or a high-power instantaneous water heater is more suitable.

When the storage device is initially turned on, it will take some time to heat the water, the flow-through ones can immediately heat from 1.8 to 4 liters per minute. They heat up the entire flow of water at once, while storage water heats the incoming cold water, which is mixed in a tank with hot water when it is consumed and after a while the temperature of the water in the tap begins to decrease.

Under-sink water heater: how to install a boiler under the sink Instantaneous water heater

That is, both types of water heaters have both advantages and disadvantages, and the choice in favor of one of them is only a matter of consumer preferences..

But for a country house, in the absence of main water supply, a gravity water heater is indispensable, which is equipped with a special small-diameter mixer to obtain a stronger jet. It is equipped with a hydraulic pressure switch to create pressure. If the summer cottage is not used in winter, it can even be removed, and reinstalled in spring – its installation is so simple.

Pipe fittings for installing a water heater

Let’s dwell a little on the pipe fittings that will be required when piping the boiler.

Security group

To protect the water heater from hydraulic network overloads, manufacturers recommend installing special fittings – a safety group that has a pressure limiter. If the pressure in the network exceeds 4.5 atm, a pressure reducer or a pressure reducing valve must be installed in front of the safety group.

Under-sink water heater: how to install a boiler under the sink Safety group for water heater

For small DHW cylinders, this element is desirable, but not required..

Non-return safety valve

The safety check valve is designed to ensure that the tank is completely filled with water, otherwise the heaters may become exposed and burn out. Drainage of water from the tank is possible when the pressure begins to drop in the line, and the valve holds the water in the tank. The second function of this valve is to drain water from the tank, for example, to repair it. The third function is tank rupture protection. Sometimes the thermostats fail, the water continues to heat up, and the pressure in the tank rises. If during this period there is no water withdrawal, then the tank can depressurize under the influence of boiling water and steam. Fortunately, this rarely happens, but it is better to take safety measures, especially since the price of this valve is incomparable with the possible consequences of an accident..

Under-sink water heater: how to install a boiler under the sink Safety valve

If the valve is not installed or has become unusable, you will immediately find out about it – hot water will flow from the cold tap. There will also be hot water in the toilet cistern, and you will pay for the electricity consumed for this heating. It is installed at the inlet of cold water to a capacitive water heater.

Advice!An arrow on the body shows the direction of water flow. When installing the boiler under the sink, the direction of the flow of cold water is downwards, which means that the drainage outlet will be directed upwards. To prevent water from dripping on the floor, install a drip funnel under it with a drainage outlet to the sewer or put a tube of a suitable diameter on the nipple and lower it into a container.

Other valves are designed to shut off cold and hot water on each of the branches of the water supply.

Attention! The water heater installed under the sink is hidden from view, and the leak can not be noticed immediately. Therefore, all water connections should be properly sealed, sealed, for example, with linen tapes, FUM tape, special paste..

Installing a water heater under the sink

The installation of different types of heaters is somewhat different. Consider the connection diagrams and installation procedure for various water heating structures.

Under-sink water heater: how to install a boiler under the sink

Installation of a pressureless water heater

The easiest way to install non-pressure boilers. They cannot be connected to a conventional mixer, connected directly to the main pipeline, since the device is not designed for the network pressure – it can break.

A special mixer for such a boiler has two valves – one regulates the temperature (mixing with the cold one), the other the flow. In this system, the mixer performs the function of a safety group: it cuts off cold water at the inlet to the heater and discharges excess water that occurs due to its expansion as a result of heating.

Under-sink water heater: how to install a boiler under the sink Mixer for gravity storage heater

Usually, when purchasing such a heater, the kit includes tubes and shut-off valves that are installed at the inlet and outlet of the tank. In this case, the non-return safety valve can be omitted (because there is no risk of a pressure surge) or simply replaced with a non-return valve. The floor heater is simply installed on the floor, while the wall heater needs to be fixed to the brackets or other fasteners supplied. Then the tubes are connected according to the scheme.

A pressureless instantaneous water heater is mounted according to the same principle. We connect the heater to the mains only after filling the water heater with water.

Installation of a pressure storage water heater

Make sure you have a grounding socket near the heater in advance. If the heater is wall-mounted, mark the mounting points on the wall, drill holes for fasteners, fix the bracket and hang the heater. The floor heater does not need to be fixed to the wall.

Under-sink water heater: how to install a boiler under the sink

We start preparing the water heater. To do this, do the following:

  1. For the cold water supply (blue mark on the tank nozzle), we mount a non-return safety valve. The direction of water on the valve is indicated by an arrow.
  2. We screw the shut-off valves onto both tank unions. In cold water, the shut-off valve is installed directly on the valve.

Attention! It is not necessary to overtighten the thread during installation, you can tear!

  1. We connect flexible piping to the valves (may be included) or through adapters, metal-plastic (polypropylene) pipes with a diameter of 16–20 mm for connecting to the water supply. The latter method is preferable, since it is more reliable and, in addition, the larger diameter of the pipes provides less hydraulic resistance and better water supply..

Next, we work with the water supply system – we mount the tees at the point of water intake after the locking taps (which are at the entrance of the pipes to the apartment):

  • on cold water – for supply to the water heater;
  • on hot water to switch from the main hot water supply to the backup.

We connect the hoses (tubes) coming from the tank with the corresponding pipes for hot and cold water. Check that it is cold to cold, and hot to hot.

Under-sink water heater: how to install a boiler under the sink 1 – hot water supply; 2 – safety valve; 3 – eyeliner; 4 – cold water supply

Connect a dropper or a siphon to drain into the sewer or a thin tube to drain into a separate container to the drain connection of the safety valve.

Before turning on the water heater, turn off the hot water tap on the mains. Connect the electricity only after filling the tank with water.

Installation of a pressure flow heater

Installation of an instantaneous water heater is similar to the installation of a storage heater. The difference is the absence of a safety check valve due to the lack of a tank. For some models, it is recommended to install a coarse or fine filter and even a water softener on the cold water supply. The device is attached to the wall, cuts in pipes with shut-off valves into the hot and cold water supply line after the network valves and is connected to the mains.

Under-sink water heater: how to install a boiler under the sink 1 – hot water supply; 2 – shut-off valve; 3 – coarse filter; 4 – eyeliner; 5 – cold water supply; 6 – RCD

Most instantaneous heaters, especially those of high power, are not equipped with an electric plug. It is assumed that the equipment must be connected through a dedicated line directly to a separate machine in the switchboard. The line must be grounded, with a short circuit protection device. The cable cross-section is selected depending on the power of the flow-through boiler.

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