Combi boilers, in short, blend the capability to provide hot water and central heating in one compact box. But before you dash out and begin googling your nearest Gas Safe registered installer, it might be a good idea to find out a bit more concerning advantages and disadvantages of a combi boiler, so please stay with me .
How do combi boilers work?
Kindly noted by A R Johnson Plumbing & Heating in Ormskirk the hot water is supplied via the cold water mains which goes through the boiler and is heated up on-demand, when I say “on demand” I mean if you want hot water you open up a tap, the boiler then heats the water before it reaches the tap outlet, after you have finished washing the dishes or taking a bath, you turn the tap off, which sends a signal to the boiler (by way of a flow switch) and the boiler stops heating the water.
The Central Heating works in much the same manner, the water is moved around the central heating circuit when you “call for heat” via a room stat/programmer, once the demanded temperature is hit the boiler turns off. All combi boilers are now condensing meaning that they cool-down the flue gases to create energy, which subsequently improves efficiency and lowers running costs , this process causes a build-up of condensation which is acidic, the condensate leaves the boiler via a plastic pipe and ends in a drain or waste material pipe (so keep in mind you need to site your new boiler near a drain).
New condensing combi boilers are fan flued, meaning that there is a fan which is used to suck the fumes in to the outside air via the flue, this procedure improves the safety of your product, as the boiler won’t “fire up” unless the fan is operating.
Benefits over a system boiler
A system boiler is a central heating boiler which uses a hot water storage tank to store hot water until the individual requires it, this is clearly costly, as contrary to a combi you’re heating the storage tank up regardless of whether your using the hot water or not, whilst with a combi its “on demand”, so the first benefit is its cheaper to operate.
The 2nd advantage is space, with a combi boiler you only have the boiler, and everything your system needs is contained inside the one box, so the tank, 3 way valve, tank pipe work, header tanks, and anything else connected with a system boiler can be taken out freeing up loads of space for storage in your house.
With a combi boiler often you will get an increase in pressure compared to your old gravity or fully pumped system (specially gravity fed) this may hinge however on your cold water pressure.
Disadvantages of a combi boiler
For the life of me I can only see just one disadvantage of a combi boiler, and that is the hot water flow rate. In a nutshell a combi is only able to produce between 10 and 16 litres of water each minute (depending on boiler size), so if you had 2 showers which were often used at the same time, then I would counsel against a combi, as one of the showers would run cold, as the boiler could not maintain the demand. If however you have just one shower or one bathroom then I would certainly propose a combi, even if you did have 2 showers/bathrooms providing you were happy to just have one in use at the same time, then a combi would still be the system I would recommend. A system boiler provides you with as much hot water as you need due to the capacity of the hot water tank.
NOTE: Some combi boilers do incorporate small storage tanks, which can combat this problem to a certain degree.
Hopefully this information has enhanced your combi boiler installation knowledge, and helps you make the correct decision. For more information speak to a local plumbing and heating engineer.