New Boiler: Getting contradictory advice about size

[fixitflav]

The problem now is that the fitter who is doing this is nervous that there might not be sufficient gas pressure to drive an 18kW and wants to stick with what is there now (12).

He should be able to calculate pressure drop at the increased gas flow. Also he could measure the pressure at the boiler with the current one at maximum output, to give an idea of any likely problem.

 

[denso13]

The mistake I made here is when I said that my current 12kW can heat the house on the coldest of days.. Thats true.. But it takes time and thats with 30% of the radiators off... I have nothing to compare it too and don't know whats possible.. But for me, it doesn't feel like there is enough 'umph', in the current system. It gets there for sure, over time.. But I believe its struggles in extreme cases.

You keep asking/saying the same thing.

The fiter can do a heat loss calculation to determine just what size you need. Or fit the Vokera Pinnacle 20s which which modulate low enough for whatever is needed.

The problem now is that the fitter who is doing this is nervous that there might not be sufficient gas pressure to drive an 18kW and wants to stick with what is there now (12)

The fitter should be able to check that very easily.

 

[jweaver]

You keep asking/saying the same thing.

I am not asking anything. I was just looking to close this discussion with a final update incase it helped anyone in the future.. But people still keep telling me I am wrong..

 

[endecotp]

A heat loss calculation / estimate of some sort should really be the start of any boiler selection process.

 

[fixitflav]

Or fit the Vokera Pinnacle 20s which which modulate low enough for whatever is needed.

That's a system boiler, current one is heat-only, so installation likely to be more complicated. And there's a lot to be said for heat-only, where the parts of the system are separate and accessible.

 

[fixitflav]

I am not asking anything. I was just looking to close this discussion with a final update in case it helped anyone in the future.. But people still keep telling me I am wrong..

But you raised the additional point about the nervous fitter!

 

[jweaver]

But you raised the additional point about the nervous fitter!

It was just an additional comment.. Sorry that mentioning another point caused offence.. I think we need to wrap this one up... We arn't getting anywhere.. Everyones points are taken on board.. However, sometimes its not as easy as implied, when you live in a rural area and the selection of fitters is small and they want to make a selection based on previous experience... I have very limited options and all of done work on the exact same houses before and have a pre-determined idea of what size is needed...

 

[denso13]

Add up the outputs of all the radiators, that could be found online easily enough. Would give you an indication of the boiler size requirements.