Advice on Gas Boiler Replacement please

EnglishMohican

The heating coil in our hot water cyclinder is leaking and the cylinder needs to be replaced. While I am about it, I thought I would replace the gas boiler which is 30 years old. Talked to 3 Heating Engineers so far. One wants to install a combi, one happy to install something but not clear what and third quoted £3000 for almost what I think I want. The water flow into the house is not adequate for a combi, the second talked well but cannot be bothered to send a written quote and the third seemed more knowledgable but cannot/will not justify his choice of boiler size.

Existing boiler is 15.5kw. There are 10 radiators of various sizes. They are all old style single panel without fins. I found some figures on internet which suggests these radiators cannot dissipate more than 7kw total. If I changed all of them for double panel with fins, they might dissipate 18kw but would struggle as the pipes cannot carry that amount of heat quietly. We keep most of the radiators we have off as we are old fashioned and like a warm living room but cool bedrooms (some not occupied in any case). A "whole of house" calculation using a spreadsheet linked from a thread on here says 6.9kw is enough to keep the whole house warm (balance the losses)

The pipes to the hot water cylinder limit the heat I can put into the hwc to 6kw maximum.

So worst case with new radiators flat out and hot water being heated as fast as possible is 24kw.

I am not planning on changing the radiators and how often would a worst case situation of everything flat out happen in any case and would it matter if the hwc heated a bit slower?

Heating engineer recommends a 30kw boiler and just says it will be better.

I would like any advice or comments on my calculations that will help me decide whether I am being the customer from hell or a hero standing up for a professional approach to choosing a new boiler.

southcoastrgi

EnglishMohican wrote: »

Heating engineer recommends a 30kw boiler and just says it will be better.

yeh ok :rotfl:

with 10 rads you would (unless they are really big) be looking at around 8 - 10 kws, so I'd be looking to put a 15kw or 18kw boiler in