Old vs New boiler ratings?

Alan Small · 4 Feb 2021

My old Apollo 50Si boiler is on it's last legs & I'm browsing for a suitable (heat only) replacement. However I'm a little confused about the KW ratings. To purchase a new boiler with similar performance which figure from my old boiler should I use as it has 2 ratings - 18.3KW input & 14.7KW output. As current boilers only seem to be advertised with 1 rating should I be looking at a 15 or 18KW unit?
Many thanks.

muggles · 4 Feb 2021

Output is the important figure. Input is how much gas you're burning, output is how much heat you get out. On modern boilers those two figures are within a gnat's whisker of being the same, assuming the boiler has been correctly selected & properly installed onto a suitable system, so there's little point quoting both.

footprints · 4 Feb 2021

It is the output you need to get right as you can see the efficiency of your old boiler is poor around 70% a new boiler will be in the high 80's here is a random boiler example if you scroll down it states output figures and the efficiency of the appliance.

https://www.vaillant.co.uk/homeowners/products/ecotec-plus-system-1024.html

Razor900 · 4 Feb 2021

When your old boilers was installed the place probably had single glazed draughty windows and no loft insulation.

Bearing that in mind you will almost certainly need a lower powered boiler than the old unit

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Old vs New boiler ratings?

Alan Small

muggles

footprints

Razor900

DIYnot Local

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