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Achieving Maximum Gas Boiler Efficiency: How to Install Your Gas Boiler the Right Way
Did you know that most gas boilers installed in the UK are oversized and running well below their advertised gas boiler efficiency ratings of 90 to 95%? Actually, most modern boilers are being installed to run below 80% efficiency!…
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How To Boost Your Gas Boiler's Efficiency Upon Installation
Did you know that most gas boilers installed in the UK are oversized and running well below their advertised gas boiler efficiency ratings of 90 to 95%? Actually, most modern boilers are being installed to run below 80% efficiency!
We, as an industry, have been dumbed down by oversized combination gas boilers that are fitted without proper commissioning — leading to lower gas boiler efficiency — that still work because ‘things get hot’. Heating engineers are now having to be taught how to design and install heating systems to maintain the high efficiencies that heat pumps can attain, with a lot of problems being caused by the untrained installing them badly. This training also helps with gas boilers.
Most homes in the UK have an actual heat loss between 6 – 8kw at design outside temperature of -3. Design outside temp is generally the worst case situation during the year where your heating has to work at its hardest to keep your house warm. During the winter months temperatures are generally closer to 9 degrees. This means that even a boiler that has been range rated will be oversized in the warmer winter months if not fitted with compensating controls, impacting overall gas boiler efficiency (more about load and weather compensation here). For reference, most combi boilers sold in the UK have a heating output of about 25kw and are left like this when installed.
The trick here is to find a boiler that can be range rated and then has a good low modulation range, plus has a pump that will either reduce it’s flow automatically, or can be set up properly through the boiler’s internal settings. It also helps if the boiler can use compensating controls to modulate its output to the required heat demand as the temperature changes. Don’t get me started on the Hive smart thermostat, which is a simple on/off thermostat and does nothing in the way of modulation!
The most popular boiler being sold in the UK right now is the ‘Ideal logic’. It has a minimum rating of about 7.1kw and a pump that runs at full speed of the time. That means that if it is installed in a small house or flat, it will always be too big for the property and will cycle on and off for its whole life.
So why does this matter?
Well it means that the boiler will always be putting too much energy into the house, your radiators will be getting too hot, and the temperature will never balance and be comfortable (have you ever noticed that you are always too hot or too cold?). Your boiler will also suffer from more thermal shock, and its components will degrade faster, further reducing gas boiler efficiency over time. This reduces the lifespan of the appliance, meaning it will need replacing sooner.
What we can do to help this
It all starts with a Heat loss survey! This will determine the heat output that is required for your property. Every house is different and the best results will always come from carrying out a proper survey. There are ‘cheat sheet’ figures that will give us a close idea of what is required and will help for on the fly results, but a proper heat loss survey will allow your whole heating system to be designed.
Once we have your heat loss (remember most houses are between 6-8kw) we then pick a boiler that can be range rated to this. Another factor here is choosing a boiler that can modulate really low. Boilers like the Viessmann 200 can modulate down to 1.7kw and trickle heat into your house at a really low level, keeping your heating nice and balanced (more comfort, yay). Other Boilers that have good modulation include Worcester Bosch 4000 and 8000 (2.7kw), Viessmann 050 and 100 (3.2kw), Vaillant Ecotec plus (2.5kw), and even some budget Vokeras modulate down to 3kw.
After range rating your boiler we then look at the pump maps, using the mass flow triangle (heating maths), to tell us how to set the pump up for the required flow rate to deliver the energy needed to heat your house. There’s no point having your pump set to 1000 litres per hour if your house is only 7kw, and only needs about 300 litres per hour to satisfy the boiler’s differential temperature (DT) of 20. This will be wasting energy, and probably causing unwanted noise and corrosion by working too hard. Some of the higher end boilers will have pump settings that change themselves to match the DT, and always alter their required flow rates to suit the energy that they are putting round your systems.
The next thing we do is to control your boiler with ‘actual controls’ that modulate the output, by working with current temperatures as they change. This is where weather and load compensation comes into play (not the Hive!).
The last thing we need to do is to turn that flow temperature down. By lowering the flow temperature and running low temperature heating systems, your gas boiler will operate in condensing mode more often, significantly improving gas boiler efficiency. By designing low temperature heating systems with gas boilers, not only are you being more efficient now, but you will be ready later down the line for a heat pump to be installed.
By doing these extra things (plus flushing the system properly upon installation) you can gain over 10% more gas boiler efficiency from your heating systems, and actually get somewhere close to the advertised efficiencies of modern boilers.
Conclusion
This blog mainly covers combi boilers, but these techniques can also be used with heating systems with hot water cylinders using priority domestic hot water (PDHW). Another article covering the topic of how many boilers really are oversized coming soon!
Oh, and don’t forget to turn that flow temperature down!
