New boiler confusion

[boilerprob]

I have had some quotes in for a new gas combi boiler. One of the quotes gives 3 different boiler choices, two of which are for 30kw boilers and the third for a 35kw boiler. Would there be any particular reason why one plumber would quote for different outputs on different boilers ?

Generally a combi needs more power to heat up quickly the water as opposed to a direct system boiler.

My view is you are better to go larger unless ridiculously large as it gives additional capacity if you extend. The boiler we went for had automatic gas adjustment to allow so sorts itself out and is proving to be incredibly efficient (wish I'd changed it years ago)

The ratings on combi boilers are specifically to do with its ability to provide hot water on demand.

I think I’m right in saying to provide heat to radiators takes only 7ish kw out of the boiler, based on an “average house”.

The more likely you are to have two hot taps running at once ( one or both could be a shower for example) you need to up the rating.

As @MarieG10 points out, you might want to go higher if you were thinking of extending one day?

If you’re replacing a traditional boiler ( one that heated a tank to give you hot water ) something to bear in mind is how far away in the piping the combi might be from the kitchen hot tap!

We didn’t think about that at all so run off a few litres of water before the hot arrives down the pipes !

Thanks for the replies. This is a straight old combi to new combi swap.
I just wasn't sure why he would specify 30 kw for boiler A and boiler B, and then 35kw for boiler C.

try running the cold bath tap into a bucket, time it, see how many litres per minute you get.

A more powerful combi is capable of delivering more litres per minute of hot water, but this is only useful if your incoming water supply provides so much.

It might also be to do with the pricing policy or available product range of different manufacturers.