RGI's different advice - Main compact eco - 25kw or 30kw

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Hi, my sister's just bought a house and is installing a budget combi, she's got two quotes and they both have different recommendations. The first guy said she needs a 30kw boiler and the second said she only needs a 25kw boiler

It's a terraced house with seven radiators (4 bedrooms). The total CH pipe run is between 35 and 40 meters (the main spine of the pipework going through the middle of the house is 22mm - then branches out into 15mm for each radiator). One bathroom, one kitchen and only one shower.

The original boiler is 30kw but the second RGI said it was oversized

So who's right?.. will 25kw be ok?
 
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CH is irrelevant - both boilers are oversized for that.
It's the hot water performance that matters, and that is personal choice as to what flow rates are desired.
 
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CH is irrelevant - both boilers are oversized for that.
It's the hot water performance that matters, and that is personal choice as to what flow rates are desired.
OK, in that case I'll tell her to go for the 30Kw.. everyone loves a hot shower!
 
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durhamplumber

:confused: interesting.. i guess the 30kw is the safer bet though
If you like..Not safer just bigger...more expensive, more water..Depends what your priority is..Some want to save water and money,,some want some sort of sensory overload, cosmic cloud burst experience to get clean.Which are you?
 
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If you like..Not safer just bigger...more expensive, more water..Depends what your priority is..Some want to save water and money,,some want some sort of sensory overload, cosmic cloud burst experience to get clean.
:ROFLMAO: good point, knowing my sister I think she's going to punt for the sensory overload rather than saving the planet!
 
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durhamplumber

:ROFLMAO: good point, knowing my sister I think she's going to punt for the sensory overload rather than saving the planet!
In that case....lights and built in sound systems are available!...Along with a head so large,a 5 minute shower costs more than a bath...(40kw combis are available!)
 
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Worth noting that the minimum output of the Main is 6.7kW, which is likely to be quite close to the maximum capacity of the heating system. The effect of this will be that it won't be as efficient as you might hope. Around 80-85% of gas bills come from heating rather than hot water production, so it's worth considering buying a boiler with a lower minimum output to improve efficiency and controllability. Invest a little more now for a return of lower gas bills going forward
 

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