Combi or combination boilers are compact devices for your domestic hot water (DHW) system and the home heating system. Both these systems are catered by the single boiler and hence the term "combi". Home Energy Saving (HES) scheme of the Sustainable Energy Authority of Ireland (SEAI) offers grants up to Euro 500 and 700 respectively for up grading the heating controls and the Gas/Oil burner Boiler. The minimum requirement of circuits for such a system is two which condition may be easily satisfied by the combined DHW and Space heating circuits. A quality A grade combi condensing boiler which can easily provide a fuel efficiency of up to 92% may be a good choice whether it is for a retrofit or a new construction.

Combi boilers are generally oil, natural gas or LPG gas burning whichever the fuel easily and economically available in your part of the country.

Are they all condensing boilers?

Heaven forbid, no! There are many conventional combi boilers in use though the current preference is for condensing type boilers. The reason is obvious. The conventional boiler with an efficiency of about 80% is not in the same class as the efficient condensing boiler.

Advantages of condensing type combi boilers

A combi boiler is nothing but a wall mounted duel functional domestic hot water and Central heating unit.

• Being wall mounted and compact it is aesthetic and matches any interior décor.

• Can cater to both the DHW and home central heating systems which normally need two different temperatures.

• As we already know they have high energy efficiencies inherent to condensing type boilers.

• Space saving as cylinders and storage tanks are eliminated.

• Can provide hot water at the turn of a tap when advanced electronic control systems are installed.

• It is very clean burning and non messy especially when the fuel is gas.

• Do not need booster pumps as the boiler is connected direct to the water mains (max. pressure 10 bar).

A few things to consider

Combi condensing boilers do look (and are) simple systems. But if your contractor makes a few wrong decisions your primary target of economy and environmental safety may be out of reach. Some facts to be aware of in this regard are:

• Your heat load used for equipment selection must be right. (For eg. The DHW load may be higher than the central heating load in general use. So selecting on the basis of the DHW load alone may be an over sizing, a common mistake often done in the past).

• Ensure your mains pressure is adequate (generally 2 bar or over).

• Ensure your water flow rate available at the combi boiler is sufficient.

• Ensure a proper heat load calculation is done for you rooms. Do not work out the central heating load by adding up the radiator capacities.

(No one custom makes radiators for your rooms .They are all standardized. So adding capacities will be again an over sizing).

• Have your water supply analysed for it’s quality if possible. You may already know whether it is hard water or not. If not at least check with your neighbours who may already be using heat exchangers and have some idea of this. If the water is hard chemical treatment may be necessary to get rid of lime salts which tend to block the heat exchanger tubes.