top of page
  • Gas Users Organisation

Set up your boiler to save money, and reduce CO2 emissions!

Updated: Aug 20, 2020

by Russell Armstrong, MCIPHE

The “KillaKilowatt” campaign is advice from Gas Safe professionals on how your domestic gas boiler can be set up, to ensure that you save money, and your house produces less carbon emissions, while still keeping warm!

The campaign is a very simple message aimed at every and anyone interested in saving money on their energy bills, reducing gas emissions & wanting to do their “bit” for the environment!

The beauty about the campaign is that it wont cost you, the consumer, a penny and it will almost immediately start to save you money on your energy bills!

A genuine something for nothing!

How? I hear you cry, what’s the catch? What’s in it for you?

How, I will go on to explain, what’s the catch? You have to turn a dial on your boiler, what’s in it for you (the campaigner)? The satisfaction that you have made a difference to everyone’s lives and done your bit for fuel poverty!

The How

Any fuel that is burnt produces gasses as a by product of the combustion process. Those gasses are hot and very often full of wet vapour. There are two types of boiler, condensing, and non-condensing (don’t worry we will explain the difference) A standard gas boiler (non-condensing) simply chucks all of those gasses out of the flue to outside. The gasses are HOT and contain energy that is about to be wasted.


Those gasses contain water vapour and that vapour (kind of like wet steam) contains energy, quite a lot of it. If you convert the wet vapour into a liquid it gives up all of that energy and you can use that to help heat your building. Or put it another way, rather than waste the energy to outside you put it into your heating water! Clever eh?

Since the 1960’s & 70’s condensing boilers have been being installed. Since 2007 they have been mandatory to fit.

The savings and why it's free energy

Well technically, its not actually free (because you have used the gas to create the heat and vapour) but you are about to stop wasting the energy, so you don’t use more of it than you should (so you don’t buy any more gas than you should – saving money)

By condensing the water vapour back into its liquid form, the “latent” energy is released.

Condensing boilers

All new boilers fitted have to be able to condense the vapour in this way. The challenge is that many DON’T!

A modern boiler comes out of the factory set to work but not necessarily in condensing mode. You will get nice hot heating water but the point is that’s not necessarily good for you, the home owner, in terms of efficiency!

Traditionally a hot water circuit was set to a flow of 80DegC and a return temperature of 70DegC and that is terrible news for this condensing concept

By simply lowering the flow temperature from your boiler to 60DegC it will be able to condense far easier and you will start to lower your gas bills.

You can do this yourself, but if you have any doubts consult a local Gas Safe registered engineer.

Sounds too good to be true?

Well, that’s what you might think, and its not as simple as that because in the dead of winter, with your heating water at 60DegC your home might not get up to your desired temperature, so in that instance, simply turn up the boiler water temperature. You wont get as much condensing and your fuel efficiency will drop during the coldest of days but your system will keep you nice and toasty.

But once the outside temperatures start to warm up, you wont need the heating water to be so hot (I wont worry you about the thermodynamics or mathematical equations) simply return the boiler thermostat back down to 60 and hey presto, you will start to reap the rewards of better efficiency. (This is called, in the trade, as part load, and usually happens during spring and autumn months)

So during the period that the house remains warm enough for you, with the heating water set at 60DegC you will benefit for approximately 5-10% energy efficiency and you will be cutting down on gas emissions, CO2 emissions and reducing your carbon footprint

Why doesn’t a condensing boiler condense automatically?

It’s a fair question and there are many reasons why, but to cut through all of that, unless your heating engineer fully understands what they are doing and how to set it up, the default is that they are factory set at a higher value. They need adjusting at point of installation (or after) to give a lower flow temperature.

Traditionally home owners like their radiators hot hot hot, and when they don’t feel the radiators hot, they think there is something wrong, but they don’t understand that by allowing your radiators to run that bit cooler, they will be saving energy!

I have smart controls my boilers already at maximum efficiency!

Well technically that’s not exactly true because “smart controllers” don’t actually automatically adjust the boiler flow temperature to take full advantage of the “part load” conditions, they simply cycle the burner on and off to stop the heating system going into what we call in the trade “over shoot” (providing too much energy too quickly causing the space temperature to go too high and overheat the occupant!)

The real “smart” controllers are fully automatic and work with the boiler to automatically adjust the boiler flow temperature to take FULL advantage of running at the lowest possible flow temperature getting the boiler into condensing mode without YOU having to make any manual adjustments. These controllers are called either weather or load compensated controllers.

If you are going to get controls make sure that to get the maximum efficiency the boiler flow temperature can be automatically adjusted by the control.

So, what do I do now and how do I check what controls I have?

If you have an older non condensing boiler, there’s nothing you can do to take advantage of this efficiency gain, but those boilers might be 20 years old now, so might be due for a change but unless your boilers playing up or breaking down, its probably best to leave it as it is for now.

If you have a condensing boiler but controls that don’t alter the “set point” temperature automatically, then simply do it yourself and turn the dial down or alter the temperature on the controller for the boiler and start to take advantage of the extra efficiency that the condensing boiler will give you.

Credit where credit’s due:

The #KillaKilowatt campaign was created by @Michael Walsh (twitter @gassafeman) #tagged by Paul Lane (twitter @HighlandLtd). The name comes from the objective to save a kilowatt of energy from every home with a condensing boiler, this would save 5200 kWatt/hrs of energy per year from UK heating, saving consumers money, and cutting carbon emissions.

Russell Armstrong is a member of the Chartered Institute of Plumbing and Heating Engineering. He is managing director of RA Tech UK Ltd, and an experienced and respected plumber, who invented hotun. See

Michael Walsh is an experienced London based engineer. See:

As Michael explained via twitter “80% of boilers in the UK don’t condense. By simply lowering the flow temp on your boiler to 60 will ensure it stays in condensing mode. This is a cost free way to save energy” The inspiration for the campaign came from a training course by Heating Academy Northampton

Paul Lane is an experienced heating engineer from Salisbury, who contributes to Betatalk podcasts on renewables sustainability, low-carbon energy, solar-heat and heat-pumps. See

Image courtesy of Radiant Controls Ltd (@RadiantControl)

244 views0 comments

Recent Posts

See All
Post: Blog2_Post
bottom of page