{"id":1,"date":"2022-09-13T20:12:19","date_gmt":"2022-09-13T20:12:19","guid":{"rendered":"https:\/\/blog.rayobrien.co.uk\/?p=1"},"modified":"2022-09-19T16:47:00","modified_gmt":"2022-09-19T16:47:00","slug":"boiler-energy-efficiency","status":"publish","type":"post","link":"https:\/\/blog.rayobrien.co.uk\/index.php\/2022\/09\/13\/boiler-energy-efficiency\/","title":{"rendered":"Boiler Energy Efficiency"},"content":{"rendered":"\n

A condensing boiler is designed to have its return flow temperature at 20C below the outward flow. This is called \u2206T20. Building Regs L state that boiler must be at least 88% efficient. Combi boilers on average in Britain run at 83% efficiency. The condensing mode of the boiler happens with a Return Flow temperature of 54% or less. <\/p>\n\n\n\n

Return Temp in \u00b0C<\/td>Boiler Efficiency<\/td><\/tr>
80<\/td>86%<\/td><\/tr>
54<\/td>88%<\/td><\/tr>
40<\/td>94%<\/td><\/tr>
20<\/td>98%<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

So Boiler is most efficient when in condensing mode and to be in condensing mode the Return Flow temp must be less than 54\u00b0C. <\/p>\n\n\n\n

Average heat loss in a house in the UK is 6kWh. 80% of properties in the UK have a heat loss below 10kWh. The most popular boiler is 30kWh which should be able to heat up 5 houses on average!!!<\/p>\n\n\n\n

Heating and Hot water Energy Needs<\/h2>\n\n\n\n

The number of people in your new home and the size of your property are the primary determiners for the amount of heat your system needs to generate. It’s better to plan for slightly more than your maximum requirements, as this will ensure that you\u2019re covered in the vast majority of circumstances.<\/p>\n\n\n\n

A rule of thumb applies when calculating your energy requirements. The kilowatt hour (kWh) is the billing unit for energy delivered to consumers by electric utilities:<\/p>\n\n\n\n

kW heating capacity (number of m\u00b2 x 50 W\/m\u00b2\/1000) + kW hot water output (approx. 30% of the heating capacity value)<\/p>\n\n\n\n

= kW rated heat output (= 6.5 + 1.95 = 8.5) (Does this apply to a combi boiler?)<\/sub><\/p>\n\n\n\n

According to this formula, for a low energy house with 130 m\u00b2 living space the result is 8.5 to 9 kW rated heat output. The rated heat output is the maximum attainable power output of a heating system in continuous operation. <\/p>\n\n\n\n

Are Boilers Overpowered?<\/h2>\n\n\n\n

A Vaillant ecofit 825 has power output as follows:-<\/p>\n\n\n\n

Central Heating Max. Output<\/td>20.4 kW<\/td><\/tr>
Hot Water Max. Output<\/td>25.4 kW<\/td><\/tr>
Flow Rate<\/td>10.5 l\/min<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

The boiler brochures normally refer to the higher number which is the Hot Water Max Output number. It appears that this boiler is overpowered by approx a factor of 3 if installed in an average house\/flat. This can cause problems of cycling (the boiler turning off and on because the boiler gets too hot as the Return Flow temperature is too high.<\/p>\n\n\n\n

The following Heating Hub<\/a> website Post covers this in more detail.<\/p>\n\n\n\n

Boiler Efficiency Video<\/h2>\n\n\n\n
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