Flue Gas Heat Recovery Systems

How do flue gas heat recovery systems work?

Flue Gas Heat Recovery Systems (FGHRS) take advantage of heat within waste flue gases resulting from the combustion of gas in your boiler. This recovered heat is used to preheat the cold water entering the boiler, thereby lowering the amount of energy needed to warm the water up to the required level.

Even the most efficient boilers available on the market today are only 90% efficient, as a result of heat lost in the waste flue gas, however the installation of a FGHRS on even a brand new boiler can help further drive up energy efficiency, helping you save money on your energy bills.

Flue gas heat recovery systems requires very little maintenance, with no need for mains electricity. They can they be used in combination with a number of renewable technologies and help cut water use by your boiler by up to 6%, which is helpful if you are on a water meter.

What can a flue gas heat recovery system do for my boiler?

Almost all modern boilers are ‘condensing boilers’. This means that they already have some sort of heat recovery type system built in, making them much more efficient than older boilers. Even so, a FGHRS can further increase the efficiency of these condensing boilers in most cases, delivering the same amount of heat with 7% less gas.

On older boilers the savings are much more substantial – for example, if you install a FGHRS on a G rated boiler you could see gas savings of up to 52%, whilst on older combis the savings can be up to 35%. In many cases, even though these savings are huge, it is probably a more economical decision to upgrade the boiler to a condensing model as well as installing a FGHRS.

Remember that not all boilers work with FGHRS and each system will be different, so you will need to check with the manufacturer to ensure your boiler is compatible.

A typical saving on an A band boiler would be around 5% on your gas bill, and we have done some worked examples to see what that would mean in terms of payback:

Modern A Band Boiler (5% saving)

Gas Usage Cost Savings through FGHRS Payback
10,000kWh (Small property) 400£/year £20 39 Years
20,000kWh (Medium sized property) 800£/year £40 20 Years
30,000kWh (Large Property) 1,200£/yr £60 13 Years

80% Efficient boiler (10% saving)

Gas Usage Cost Savings through FGHRS Payback
10,000kWh (Small property) 400£/year £40 20 Years
20,000kWh (Medium sized property) 800£/year £80 10 Years
30,000kWh (Large Property) 1,200£/yr £120 7 Years

As you can see, even without the GDHIF, it is a great addition to your boiler if you live in a large property.


    • Helps improve the efficiency of your heating system by recovering heat from flue gases.
    • Use less gas for the same temperature.
    • Fit and forget technology, very little maintenance required.


    • Payback time is not particularly cost effective, unless you use a lot of gas.


    • From £1,000 for unit and installation.