Traditional central heating systems have a hot water storage tank (in an airing cupboard) and a feed and expansion tank (located in the loft). Having a hot water storage ability allows these systems to deliver large amounts of hot water at short notice. The hot water capacity is only limited by the size of the hot water tank and the ability of the boiler to renew the hot water when depleted.
The additional components and hot water storage also contribute to reduced energy efficiency, higher installation costs and a more complex system. You need more space if you have a traditional central heating system and the additional system components are all potential problems at some point in the future.
To counteract these deficiencies the combination or combi boiler was developed. This type of boiler heats hot water on demand whenever the hot water tap is turned on. This means that the supply of hot water is not limited and there are far fewer components in the central heating system.
Fewer components and no hot water storage all contribute to a lower cost installation with a better energy efficiency, resulting in lower ongoing heating costs. Fewer components mean that there are fewer parts which can break down at some inconvenient moment.
One disadvantage is that the hot water flow rate of a combi boiler will not match that of a conventional boiler. Water has to be heated on demand and hence it may take longer to run a bath although a shower will be a pleasant surprise as the hot water is delivered at mains pressure giving a high power spray. Heating water on demand has another downside in that there is a limited capacity for hot water production at any one moment. This is okay in houses with smaller families or single person occupancy but it can be a problem with larger houses and larger families where several hot taps may be turned on at the same moment and the demand for hot water is greater than the hot water production capability of the combi boiler.
Another issue to consider is the temperature of the hot water. This can be influenced by the temperature of the incoming cold water and the flow rate. As a result it is essential that the power of a new boiler is matched to your heating needs.
Some advanced combi boilers incorporate a small hot water cylinder. Installation is still easy with reduced components but the boiler stores some hot water to enable it to meet initial demands for hot water.
If you are considering getting a new boiler but do not know which type would be rightfully you there is the opportunity to get expert advice from the main boiler installation companies. They will insist upon sending ground one of their heating advisers to do an audit of your property and get their foot in the door so that they can give you a “no obligation” quotation. You may feel that this is a price worth paying, spending an hour of your evening with the heating adviser, as the end output will be a firm quotation based upon your requirements and knowledge of which type of boiler and what size is best suited to your home.