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.

FGHRS and the Green deal home improvement fund

UPDATE: As of 30 March 2016, the government has stopped funding and the Green Deal Home Improvement Fund is closed to new applications. 

FGHRS start from around £650 + VAT, meaning that through the GDHIF (new green deal cashback), you can get a whopping £1,600 cashback just by installing a FGHRS worth £650 + VAT (plus the condensing combi of course). The reason this is the case is because the GDHIF requires a dual measure approach – the new boiler being one and the FGHRS being the 2nd. Without it the new boiler would cost, give or take, around £2,000 without any cashback available. However, with the FGHRS, the job will cost around £2,780 but with a massive £1,600 cashback available. This has made going down the Green Deal route an incredibly good idea as it makes installing an efficient boiler incredibly cheap.

In order to qualify for the GDHIF, you must have a Green Deal Assessment. If you would like to book an assessment then please fill out the form found at the bottom of the page:

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. However, it becomes a no-brainer when used in conjunction with the green deal home improvement fund.


    • Helps improve the efficiency of your heating system by recovering heat from flue gasses.
    • 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