Passive Flue Gas Heat Recovery Devices enable you to reuse heat from your boiler that would otherwise be wasted. They are retrofit devices for older boilers that capture waste heat from flue gases and reuse it, to improve the efficiency of hot water production and save fuel and money.
Normally, flue gases escaping to the atmosphere can exceed 60°C. Passive Flue Gas Heat Recovery Devices reclaim much of this wasted heat, letting the flue gases then vent to the atmosphere much cooler.
A heat exchanger is fitted around the flue coming from the boiler to heat up mains cold water that is fed into it.
The heated water is then either stored for use later in a tank, or used as pre-heated incoming water for the boiler so it has less work to do.
Passive Flue Gas Heat Recovery Devices can work on boilers whatever their fuel (depending on the model and flue size). But not all boiler types are suitable. Exact savings depend on the type of boiler to which they are fitted:
Chris Farrell, MD of Zenex Technologies, and inventor of GasSaver, the model used by Baxi and others, believes these devices can provide help reduce fuel poverty by substantially reducing fuel bills.
Passive Flue Gas Heat Recovery Devices are listed under SAP appendix Q with an independently assessed, additional energy saving rating.
Besides GasSaver, other makes are: Vaillant’s recoFLUE and Energycatcher Combiplus.
The difference between the GasSaver and the Energycatcher is that with the latter, the reclaimed heat can be stored in a tank and used when required, in much the same way as a solar thermal system. With the former, it pre-heats the water used by the boiler.
Not all devices fit all boilers. To find out which is the one for yours, or if yours is able to have a retrofit, first make a note of the type and model number of your boiler, then visit the suppliers’ or manufacturers’ websites where there is a list of which models of boiler their devices are suitable for.
Fitting instructions are different for each device. Follow the instructions in the technical manual.
Costs start at around £1,200. Payback time depends on the type of boiler and usage level, and whether you fit it yourself or get in a plumber.
You’ll save more money if you have a water meter, since less water is used.
Before buying one, check what type of boiler you have, to see what savings are possible. Since 2005 virtually all gas boilers that have been fitted in the UK have been more efficient, condensing boilers.
Condensing boilers have bigger heat exchangers that already recover much heat from the burning gas, making them more efficient than non-condensing ones.
Combi boilers heat water on demand and don’t need a tank to store hot water.
How to tell if your boiler is a condensing boiler:
© David Thorpe Jan 2013. David is author of Sustainable Home Refurbishment: The Earthscan Expert Guide to Retrofitting Homes for Efficiency
Also See:
Biomass boilers, combi boilers, condensing boilers at free eco open house events in September
Green boilers