KIBA Kitchen & Bathroom Designs Ltd.

119 Addington Road  
South Croydon



Tel.: +44 20 86571222

Business hours

Monday - Friday 10.00 - 17.00

Saturday 10.00 - 14.00

Call us for free bathroom and kitchen quotes Design service available

Tel.: +44 20 86571222


What is the right hotwater/heating system for you?


Combi Boiler

A combi boiler combines a highly efficient water heater and a central heating boiler into one compact unit. As a result, the combi boiler is fast becoming the heating system of choice in new homes across the UK, with over 50% of new installations being this type of boiler.

Combi Boilers and Storage Space

Combi boilers provide central heating and hot water without the need for a hot water cylinder in an airing cupboard or a cold water tank in the loft. The combi boiler is not only an ideal space saving solution (as the combi boiler unit is very compact), but also it limits the heat that escapes as waste compared to traditional models, via things like the hot water tank.

Combi Boilers and Heating Hot Water

Combi boilers take water from the mains and then heat it as required, but are on standby when there is no water demand. Therefore hot water is available 24/7 and also just as importantly, the water is delivered at mains pressure, so no pump is required to deliver the 'power shower' experience (provided your home has adequate mains water pressure).

To produce the hot water that comes out of the taps, the cold mains water passes over a highly efficient heat exchanger. The heat exchanger transfers the vast majority of the heat from the burnt gas (90% or more) to the cold water, and then delivers it to the taps as required. Since combi boilers do away with the hot water tank, they are much more energy efficient, since there are no heat losses associated with stored hot water, it is simply created as needed.

Combi Boilers and your Central Heating System

On the central heating side, combi boilers pump the water round the heating system in a completely sealed system. The boiler incorporates an expansion tank internally, so there is no need for an external feed and expansion tank in the loft, which obviously saves a great deal of space.

One of the issues with a combi boiler is that they struggle to produce both hot water and central heating at the same time, so priority is given to your domestic hot water whenever a hot water tap is opened in the home. For example, if you are running a bath, during this time no hot water will be circulated through your heating system, but as soon as the bath is full, the central heating circulation will resume.

Our recommendation: Combi boilers may be your right choice if you do not have more than one bathroom.

Vented hot water systems

Vented hot water tanks are still the most common type of hot water systems found in the UK. Unlike the newer unvented tanks, these copper tanks are fed by cold water from a header tank (normally located in the loft) and they use gravity to drive the hot water around the home. A vent pipe links the vented hot water cylinder and the cold water in the header tank.

As with the unvented system, expansion of warm water is still an issue, but in this case the expansion simply takes place via the vent pipe and in the header tank.

The hot water pressure tends to be governed by the height of the water tank above the tap or shower feed, which means that although on the ground floor of the home the pressure might be excellent – in rooms on upper floors the pressure will be lower. As a result many showers in homes with vented hot water tanks use electric pumps to drive the hot water to the shower at increased pressure.

Vented hot water cylinders are far less complicated than the pressurized vented systems and for this reason they are much simpler to maintain and install – making them a cheaper option when compared to the unvented system.

Indirect Systems

Most hot water cylinders are heated via an external heat source such as a gas boiler or solar thermal. In this case the hot water is heated and then travels through a copper coil in the hot water tank. The heat is then transferred from the from the external heat source to the water inside the hot water tank.

Indirect cylinders tend to be fitted with a direct backup (such as a immersion heater) – so even if the boiler is broken you can still produce hot water as and when you need it.

You can get both vented and unvented indirect systems.

Direct Systems

In a direct cylinder system, the hot water is heated directly by an internal element such as an immersion heater. The hot water tends to be more expensive to produce in direct systems. Some homes have no access to gas, for example a mid-level flat, in this case they are forced to go with a direct system for their hot water, so they may choose to take advantage of Economy 7 which will give them a cheaper electricity at night to heat the hot water with.

Normally this type of cylinder would be fitted with two different immersion heaters, one for the peak electricity and one for the off-peak electricity. If this is the case, you really need to make sure that the immersion heaters are set up on the timers correctly to ensure you are paying the least possible for the hot water. There is no point heating water via your peak immersion heater during the middle of the night.

Our recommendation: If you have already a vented hot water system and want to have a good water pressure you should install a pump. If you have more than two bathroom or you plan in the nearer future another one we would definitely recommend an unvented hot water cylinder.

Unvented hot water cylinders (i.e. Megaflo)

Unvented hot water cylinders were only made legal in the UK in 1986, but have since rapidly grown in popularity. In an unvented system there is no cold water tank – instead the sealed hot water cylinder is fed directly by the cold water mains. Since they are operating at mains pressure, they offer much better flow rates meaning your shower and bath performance should be higher.

The other major benefit is that you don't need to maintain a cold water tank in the loft (which vented systems require). This is good news since not only does it free up space, it also removes the potential freezing issue during our long cold winter periods.

In addition, since you aren't relying on gravity to move the hot water around the home, the unvented cylinder can be located pretty much anywhere in your property.

Other advantages of installing an unvented system include reduced noise in the system since there is no cold water filling of the water storage cistern, and since there is no water storage cistern and the system is essentially sealed, the cold water is not at risk from contamination.

Unvented Water Cylinders and the water expansion issue

Since water increases in volume as it gets warm, unvented cylinders need to include a mechanism that allows the expansion to take place thereby keeping the cylinders operating at a safe pressure.

There are two methods of allowing this expansion to take place safely. The first is the bubble top unit, which uses an internal air bubble that is produced and trapped at the top of the cylinder when it is installed. The other type is the external expansion unit that utilizes an expansion vessel to contain the expanded hot water.

The major issue with unvented hot water cylinders is that since hot water flow depends on the cold water main pressure – if for any reason there mains water is turned off, your home will be without access to any hot water.

Since unvented hot water tanks are operating at higher pressure than the vented systems and have additional safety features installed, these cylinders need to be installed by boiler specialists holding a qualification that complies with G3 of building regulations, which means they are more expensive to install them as traditional vented hot water systems.

Our recommendation: If you have more than one bathroom and you want to install a new hot water/heating system you should decide for an unvented system as it is space saving, energy efficient and gives you a good water pressure.

How to calculate the requirede radiator heat-output per room?

What is the perfect temperature for a room?

Lounge: 21 °C (70 °F)

Bedroom: 18 °C (64.4 °F)

This is the common preferred temperature but it varies depending on personal preference.


What is a BTU?

A BTU is the amount of heat required to raise the temperature of 1 pound (0.454 kg) of liquid water by 1 °F (0.56 °C) at a constant pressure of one atmosphere.


Calculate the radiator heat-output for a room:

This information will provide you a guide to the output required both in BTUs and Watts, for a specified room.

Multiply the width with the length and the height of the room. It requires to measure in metres.

The result is the volume of the room in cubic metres.

For example: If the room is 3m wide, 4m long and 2.5m high the volume is 30m3.

As you need in average 85 BTUs heat-output per cubic metre you multiply the 30m3 of the room with 85.

The required radiator for the 30m3 room should have an output of 2550BTUs.

If you now divide 2550 by 3.41214 you will get the heat-output in Watt (747 Watt)

as 1 Watt is approximately 3.41214 BTU/h.


Please note:

This is only a rough estimate. Your boiler should be sufficient to supply all radiators to the sum of their maximum demand.

You should also consider factors like the shape of your room, insulation conditions, external walls, heated adjacent rooms and other factors.

Larger rooms may require more than one radiator positioned evenly throughout the room.

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